NCERT Solutions Class 8 Science Chapter 4 Electricity Magnetic and Heating Effects

F R E E S T U D Y M AT E R I A L F O R E V E R Y S T U D E N T

CLASS 8 · SCIENCE

NCERT Solutions

Chapter 4: Electricity: Magnetic
and Heating Effects

NCERT Textbook — Curiosity

BOOK PAGES SECTIONS QUESTIONS MEDIUM

46 – 61 16 44 English

Solutions, notes, sample papers & more at 42 pages

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

CLASS 8 · SCIENCE · CURIOSITY

NCERT Solutions — Chapter 4: Electricity: Magnetic and
Heating Effects
Complete NCERT Solutions for Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects from the
NCERT textbook Curiosity. Every question the chapter asks is answered here — the four Probe and ponder
questions on page 46, all six activities (Activity 4.1 to Activity 4.6), both Think like a scientist boxes, the A
step further question on the Earth's magnetism, every question in the speech bubbles from pages 49 to 56,
all eleven questions of Keep the curiosity alive and the three Discover, design, and debate tasks — each
with the observation, the reason behind it, and the mechanism worked out step by step.

TEXTBOOK BOOK PAGES

Curiosity (Class 8) 46 – 61

SECTIONS QUESTIONS

16 44

MEDIUM

English

Probe and ponder — Page 46
Chapter opener

PROBE AND PONDER

Q1 If we don't have an electric lamp while making an electric circuit with an electric
cell, is there any other way through which we can find out if current is flowing in
the circuit?

Yes. Place a magnetic compass close to the wire of the circuit — just below it is best — and
watch the needle as you close the switch.

If the needle swings away from its usual north–south direction, current is flowing.
If the needle stands still, no current is flowing.
Open the switch again: the needle should return to its original direction.

Why it happens: a current carrying wire produces a magnetic field around it. The
compass needle is itself a tiny magnet, so it is turned by that field. No current means
no field, and the needle simply points north–south as usual. This is exactly the test
you carry out in Activity 4.1.

Page 1 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Tip: a second, rougher test is the heating effect — a thin nichrome wire in the circuit
becomes warm when current flows. The compass test is better because it is instant,
needs no touching, and works even for a very small current.

Q2 Is it possible to make temporary magnets? How can these be made?

Yes. A temporary magnet is made by winding a coil of insulated wire around an iron nail and
passing current through it — this is an electromagnet.

1. Take about 50 cm of flexible insulated wire and an iron nail.
2. Wind the wire tightly around the nail, turn after turn, all in the same direction.
3. Connect the two free ends of the wire to an electric cell for a few seconds only.
4. The nail now picks up iron paper clips. Disconnect the cell and the clips fall off.

Why it is temporary: the magnetism comes from the current, not from the nail.
Each turn of the coil makes its own magnetic field, and because every turn is wound
the same way, these fields point the same way inside the coil and add up. The iron
nail sitting in that field becomes a magnet itself and makes the whole thing much
stronger. The moment the current stops, the coil's field vanishes and the iron loses
almost all its magnetism — so the clips drop.

Did you know? This is exactly how a lifting electromagnet on a crane works. The
operator does not have to prise the load off the magnet — he simply switches the
current OFF.

Q3 We can generate heat by burning fossil fuels and wood; but how is heat generated
in various electrical appliances?

In an electrical appliance nothing burns. The heat comes from the heating effect of electric
current.

Page 2 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Why it happens: when current flows through a conductor it faces some opposition,
called resistance. In pushing past that resistance, part of the electrical energy is
converted into heat energy, and the conductor gets hot. The greater the resistance,
the more heat is produced for the same current.

Every heating appliance therefore contains a rod or coil of wire called the heating element,
usually made of nichrome, which offers far more resistance than copper of the same size and
length. In an electric room heater or a stove you can see this element glowing red hot.

BURNING WOOD OR FOSSIL FUEL ELECTRICAL APPLIANCE

Chemical energy of the fuel is released as heat by burning Electrical energy is converted into heat by resistance

Gives smoke, soot and ash Gives no smoke, soot or ash

Hard to switch off or control quickly Heat starts and stops with the switch

Q4 How do we know if a cell or a battery is dead? Can all cells and batteries be
recharged?

A cell is dead when the chemicals inside it have been used up, so it can no longer supply
electricity. You can tell in these ways:

A lamp or LED connected to it does not glow, or glows very dimly.
An electromagnet made with it will not lift paper clips.
A compass placed near the circuit wire shows little or no deflection.
A device that used to run for hours now stops after a few minutes.

No — not all cells and batteries can be recharged.

TYPE CAN IT BE WHAT TO DO WHEN IT IS FINISHED
RECHARGED?

Dry cell (torch, clock, remote) No — it is a single use Dispose of it at an e-waste facility
cell

Rechargeable battery (phone, Yes — many times over After many charge cycles it slowly wears
laptop, inverter, vehicle) out; then send it for recycling

Page 3 of 42

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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

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Why a rechargeable battery still does not last forever: each charge and discharge

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holds acids and metals such as lead, cadmium, nickel or lithium. Thrown into

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ordinary garbage these can cause lafires or harm the environment, and valuable
material is wasted. Always hand used batteries to an e-waste recycling point; ask
your teacher if you are not sure where one is.
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Frame questions that begin with why, how .or
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a as you read.
chapter, so keep them beside you

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Does the compass needle deflect the same amount however far
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Section 4.1, Activity 4.1

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it is from the wire?
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more clips? debate, page 61
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Why does the coil pick up iron clips but not a plastic Section 4.1.1 — only magnetic materials are
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gl a attracted

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Why is the heating coil of a heater made of nichrome and not Section 4.2, page 53
of copper?
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Can a potato or a tomato light an LED, the way a lemon does? Activity 4.6; Discover, design, and debate, page 61

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Activity 4.1: Let us investigate — Pages 47–48
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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Section 4.1 Does an Electric Current Have a Magnetic Effect?

ACTIVITY

Q1 While watching the compass needle, move the switch to 'ON' position to allow
electric current to flow through the wire (Fig. 4.1b). What do you observe?

Page 5 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

nail nail

E
wire
N S

W
switch (OFF)
magnetic compass

− +
cell
(a)

nail nail

E
wire
N S

W
switch (ON)
magnetic compass

− +
cell
(b)

Fig. 4.1, page 47 — redrawn sketch of the two photographs: the same circuit with (a) the
switch OFF and (b) the switch ON. The compass lies under the straight wire stretched
between the two nails.

Page 6 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

The moment the switch is closed, the compass needle is deflected — it turns away from the
north–south direction in which it was resting and settles at an angle to the wire.

current in the wire
nail nail

N

compass

cell switch ON

Activity 4.1 — with the switch ON, the needle of the compass placed under the stretched wire turns
away from north–south.

Why it happens: a current carrying wire produces a magnetic field in the region
around it. The compass needle is a tiny magnet, so it is acted on by this field and
swings out of its resting direction. The deflection is a signal that current is flowing —
nothing touches the needle, and the effect passes straight through the cardboard
between the wire and the compass, because cardboard is a non-magnetic material.

Q2 Now again while watching the compass needle, move the switch to 'OFF' position.
What do you observe this time?

The needle returns to its original direction — it swings back and once again settles along the
north–south line.

Page 7 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Why it happens: switching OFF breaks the circuit, so the current stops. With no
current there is no magnetic field around the wire, and the only magnet left acting
on the needle is the Earth itself. A freely turning magnet in the Earth's field rests
north–south, so that is where the needle goes back to.

Tip: notice how quickly the needle responds. The magnetic effect appears and
disappears with the current — it is not stored in the wire.

Q3 Move the switch between 'ON' and 'OFF' positions a few more times. Carefully
observe how the compass needle behaves the each time.

The needle behaves the same way every time: it kicks out of the north–south direction at each
ON, and comes back to it at each OFF.

SWITCH CURRENT IN THE MAGNETIC FIELD AROUND THE COMPASS
WIRE WIRE NEEDLE

ON Flows Present Deflected

OFF Does not flow Absent Back to north–south

Why repeating matters: a single observation could be an accident — a draught of
air, or a magnet somewhere nearby. Repeating the ON–OFF cycle several times and
getting the same result each time shows that the deflection is genuinely linked to
the current and to nothing else. This is exactly the checking that Hans Christian
Oersted did in 1820 before publishing his discovery.

In-text Questions — Page 49

Page 8 of 42

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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Section 4.1.1 Electromagnets
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Why it works: we have just seen that a current carrying wire produces a magnetic
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Activities 4.2 and 4.3 are exactly this test: wind a coil, switch the current ON, and see the coil pick
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Activityo4.2:
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Section 4.1.1 Electromagnets

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you can lift a small chain of them clear of the table.
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Why it happens: current in the coil makes a magnetic field; the iron nail sitting
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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Safety and care: the book warns you not to keep the wire connected to the cell for
more than a few seconds — otherwise the cell weakens quickly, and the wire itself
begins to get warm.

Q2 Disconnect the wire from the cell to stop the flow of electric current in the wire. Do
the clips fall down?

Yes — the clips fall off at once.

Why it happens: the magnetism was never stored in the nail; it was being produced
by the current. Break the circuit and the current stops, so the coil's magnetic field
disappears. The iron nail then loses almost all of its magnetism, there is nothing left
to hold the clips, and they drop. This is what makes an electromagnet a temporary
magnet — and it is precisely the property a crane operator needs.

Activity 4.3: Let us experiment — Pages 49–50

Page 10 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Section 4.1.1 Electromagnets

ACTIVITY

Q1 Connect the two ends of the coil with the terminals of the cell as shown in Fig. 4.3c
and observe the magnetic compasses. Do you find any deflection in the needles of
the compasses?

coil on a paper cylinder

S S

E W E W

N N

magnetic compass magnetic compass

− +
cell

Fig. 4.3(c), page 50 — redrawn sketch: the two ends of the coil connected to the
terminals of the cell, with a magnetic compass at each end of the cylinder.

Yes. Both compass needles are deflected as soon as the coil is connected — even though the
coil is only wound on a paper cylinder and there is no iron in it at all.

Why it happens: the coil is now carrying a current, so it produces a magnetic field.
Each of the 50 turns contributes its own field and, because every turn is wound in
the same direction, the fields add up along the axis of the cylinder. The result is a
field strong enough to turn the needles at both ends. The paper cylinder plays no
part in this — it is only a former to hold the shape of the coil.

Page 11 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Check it yourself: the two needles turn in opposite senses, because they are facing
the two different ends of the coil. That is your first clue that the coil, like a bar
magnet, has two ends of opposite kind.

Q2 Disconnect the wire from the cell. Do the needles of the compasses come back to
their original positions?

Yes. Both needles swing back and rest once more along the north–south direction.

Why it happens: with the cell disconnected there is no current, so the coil produces
no magnetic field. The only magnet acting on the needles is the Earth, and a freely
turning needle in the Earth's field settles north–south. The coil is magnetic only while
the current flows.

Page 12 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Q3 Insert an iron nail in the paper cylinder (Fig. 4.3d) and repeat the steps. Is there any
difference in the deflection of the compass needles?

coil on a paper cylinder

S S

E W E W

N N

magnetic compass magnetic compass

− +
cell
iron nail

Fig. 4.3(d), page 50 — redrawn sketch: the same coil and cell, now with an iron nail
pushed through the paper cylinder.

Yes — the deflection is much larger with the iron nail inside than with the empty paper
cylinder, for exactly the same cell and the same coil.

CORE INSIDE THE COIL DEFLECTION OF THE COMPASS CAN IT HOLD
NEEDLES CLIPS?

Nothing (air, paper cylinder Small No, or barely
only)

Iron nail Much larger Yes

Why the iron makes such a difference: iron is a magnetic material. Placed inside
the coil's magnetic field, the nail becomes a magnet itself, and its magnetism is
added to the field the coil was already making. The total field is therefore far
stronger than the coil alone can produce — which is why, for practical use, most
electromagnets are given an iron core.

Page 13 of 42

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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Section 4.1.1 Electromagnets

IN-TEXT

Q1 Does electromagnet also have two poles like a bar magnet?

Yes. Like a bar magnet, an electromagnet has two poles — North and South, one at each end of
the coil.
This is what Activity 4.4 shows. Hold a compass near end A: one particular pole of the compass
needle is attracted to it. Since unlike poles attract, that tells you what end A is. Repeat at end B
and you find the opposite pole — so the two ends of an electromagnet are always of opposite
kind, exactly like the two ends of a bar magnet.

Why there are two: the field of an electromagnet is produced by current going
round and round the coil in one sense. That sense is fixed, so the field comes out of
one end of the coil and goes in at the other — giving one North end and one South
end. Reverse the direction of the current and the two poles swap over, which is
something a bar magnet can never do.

Activity 4.4: Let us investigate — Pages 50–51
Section 4.1.1 Electromagnets

ACTIVITY

Q1 Connect the coil to the cell and observe the compass. Note down which pole of the
magnetic compass is attracted to end A.

In the set-up shown in Fig. 4.4a it is the north pole of the compass needle (the red tip) that
swings towards end A.

North pole of compass is attracted to end A

Unlike poles attract

Therefore end A is the South pole of the electromagnet

Page 15 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Why this is a valid test: you already know from Grade 6 that unlike poles (North–
South) attract and like poles repel. The compass needle is a magnet whose poles you
know. So whichever pole of the needle is pulled towards end A must be the opposite
of end A — the needle is being used as a ready-made pole detector.

Check it yourself: your own coil may give the opposite answer, and that is not a
mistake. Which end is North depends on the direction in which you wound the wire
and on which way round you joined the cell. Record what your compass shows.

Q2 Repeat this procedure to find the polarity of end B as well (Fig. 4.4b). Did you find
that the polarity of end B is opposite to the polarity of end A?

A B

S

E W

N

magnetic compass

− +
cell
(b)

Fig. 4.4(b), page 51 — redrawn sketch: the magnetic compass now placed near end B of
the same electromagnet.

Yes. At end B the other pole of the compass needle is attracted, so end B is the North pole while
end A is the South pole.

Page 16 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

END OF THE POLE OF THE COMPASS NEEDLE ATTRACTED POLARITY OF THAT
COIL TO IT END

A North South

B South North

Why they must be opposite: the same current goes round every turn of the coil in
the same sense, so the coil's magnetic field runs along the axis in one direction only
— out at one end and in at the other. A magnet cannot have two North ends. That is
why an electromagnet, just like a bar magnet, always has one North and one South
pole.

Think like a scientist — Page 51
Section 4.1.1 Electromagnets

THINK LIKE A SCIENTIST

Q1 Repeat Activity 4.3 with — (i) 2 and 4 cells with the same coil, (ii) 2 cells but different
number of turns of the coil. What do you observe?

Both changes make the electromagnet stronger: the compass needle deflects more and the coil
holds more clips.

WHAT IS WHAT YOU OBSERVE REASON
CHANGED

1 cell Small deflection; only a few A single cell drives only a small current, so the
clips field is weak

2 cells Larger deflection; more clips A battery of 2 cells drives a larger current, so
the field is stronger

4 cells Larger still Still more current, still stronger field

2 cells, more turns on Stronger again, without Each extra turn adds its own field to the total
the coil changing the cells

Page 17 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Why it happens: the magnetic field of the coil is produced by the current going
round the turns. Increase the current and each turn contributes more; increase the
number of turns and there are more contributions to add. Either way — or both
together — the field inside the coil grows, so the needle swings further and more
clips can be held.

Tip: keep the compass in exactly the same place each time, otherwise you are
changing two things at once and cannot say which one caused the difference.

Q2 Also, repeat Activity 4.4 by changing the direction of the current.

Reverse the connections to the cell and the deflection of the compass needle reverses too: the
pole of the needle that used to be attracted to end A is now pushed away, and the other pole is
attracted instead. In other words, the poles of the electromagnet have swapped over — what
was South is now North.

Why it happens: the sense in which the current goes round the coil decides which
end of the coil is North. Reverse the current and you reverse that sense, so the two
poles exchange places. The size of the deflection does not change, because the
amount of current is the same as before — only its direction has changed.

Putting the whole box together:

The strength of an electromagnet is changed by changing the current, the number of turns,
or both.
The polarity of an electromagnet is reversed by reversing the direction of the current.

Did you know? A permanent bar magnet can do neither. Being able to change
strength and polarity at will is exactly what makes electromagnets so useful in bells,
motors, loudspeakers and cranes.

A step further — Page 51

Page 18 of 42

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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

The Earth as a magnet
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Many migratory birds, fish and animals use it to navigate across continents and oceans.
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Switches the current ON The electromagnet becomes a magnet and lifts the iron or steel objects

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Switches the current OFF

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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

They are widely used in factories and scrap yards, to move, lift and sort heavy metal items
efficiently.

Why an electromagnet and not a permanent magnet: a permanent magnet
would hold the load and never let go. Because the electromagnet's magnetism exists
only while the current flows, the operator can pick up a tonne of scrap at one place
and drop it at another by doing nothing more than flicking a switch.

Q2 While doing the activity for electromagnet, did you also notice that the wire ends
got warm? Why would that happen?

Yes — and that warmth is the heating effect of electric current, the second effect this chapter is
about.

Why it happens: when current flows through any conductor, it faces some
opposition, called resistance. Because of this resistance, part of the electrical energy
is converted into heat energy inside the wire, and the wire becomes warm. It
happens in every current carrying wire — the coil of an electromagnet included. In
the electromagnet activity the coil is connected straight across the cell, so a fairly
large current flows and the warming becomes easy to feel at the ends.

Tip: this is also why the book tells you not to keep the coil connected to the cell for
more than a few seconds. The energy going into heating the wire is energy taken
from the cell, so the cell weakens quickly.

Activity 4.5: Let us observe — Pages 52–53
Section 4.2 Does a Current Carrying Wire Get Hot?

ACTIVITY

Q1 Touch the nichrome wire. What do you feel?

With the switch still in the OFF position, the nichrome wire feels cool — it is at room
temperature, no different from the cardboard or the nails around it.

Page 20 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Why this step matters: this is your reference reading. Unless you know how the
wire feels before any current flows, you cannot honestly claim afterwards that the
current made it warm. Every good experiment begins by recording the starting
condition.

Q2 Move the switch to ON position for about 30 s and then move it back to OFF. Touch
the nichrome wire momentarily (Do not hold the nichrome wire). What difference
do you feel?

Now the wire feels distinctly warm. Repeat the ON–OFF cycle and you get the same result each
time, which confirms that the warmth is caused by the current.

Why it happens: the nichrome wire offers resistance to the current passing through
it. Because of that resistance, some of the electrical energy is converted into heat
energy in the wire, and the temperature of the wire rises. This warming of a
conductor when current passes through it is called the heating effect of electric
current. Nichrome is chosen for this activity precisely because it offers higher
resistance than a copper wire of the same size and length, so the heating is large
enough to feel in 30 seconds.

Safety first (from the book, page 53): Do not touch the wire for an extended period
to avoid any injuries. Touch it only momentarily, and do not hold the nichrome wire.

How much heat is produced depends on the material, the thickness and the length of the
wire, the magnitude of the current, and the duration for which the current flows.

Think like a scientist — Page 53

Page 21 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Section 4.2 Does a Current Carrying Wire Get Hot?

THINK LIKE A SCIENTIST

Q1 Repeat Activity 4.5 with a battery of 2 cells. What do you notice? For the same
duration, does the wire heat up more with one cell or two cells?

The wire heats up more with two cells. For the same 30 seconds, the amount of heat generated
in the experiment with 2 cells is greater.

Why it happens: a battery of two cells drives a larger current through the nichrome
wire than a single cell does, and the heat generated depends on the magnitude of
the electric current. More current through the same wire for the same time means
more electrical energy converted into heat, so the wire ends up hotter.

Altogether, the heat generated in a wire depends on:

the material of the wire (nichrome heats far more than copper);
the thickness of the wire;
the length of the wire;
the magnitude of the current;
the duration for which the current flows.

Safety first: the book states plainly that this activity should be carried out strictly
under the supervision of a teacher. With two cells the wire gets hotter than before,
so touch it only for an instant and never hold it.

In-text Questions — Pages 55 & 56
Section 4.3 How Does a Battery Generate Electricity?

IN-TEXT

Q1 Yes, but have you ever wondered what is inside these cells and batteries that
produces electricity?

Inside every cell there are two electrodes of different materials dipped in an electrolyte, and it is
the chemical reaction between them that produces the electricity.

Page 22 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Voltaic cell Dry cell

Metal cap (+)
Electrode 1 Electrode 2

Carbon rod

Electrolyte paste

Electrolyte
(liquid)
Zinc
container
Glass container (−)

Both kinds of cell have the same three parts — two different electrodes and an electrolyte. In a dry
cell the electrolyte is a thick moist paste instead of a liquid.

Why the arrangement produces electricity: the two rods must be of different
materials. Each reacts differently with the electrolyte — usually a weak acid or a salt
solution — and this difference sets up a push that drives current through the outside
circuit, from the positive terminal, through the lamp, and back to the negative
terminal. Over time the chemicals that take part in the reaction get used up, and the
cell then stops working; it is called dead.

Did you know? This is why Galvani's frog leg twitched when copper and iron
touched it, and why Volta could still get a current after replacing the frog leg with
saltwater-soaked paper. The electricity came from the two metals and the liquid, not
from the frog — and that discovery gave us the first battery.

Q2 Can we also make our own Voltaic cell using easily available materials?

Yes — a lemon, a copper wire and an iron nail are enough. That is exactly what you build in
Activity 4.6.

Electrodes: the copper wire and the iron nail — two different metals, as a Voltaic cell
requires.

Page 23 of 42

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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Electrolyte: the lemon juice, which is a weak acid and helps conduct electricity. A salt
co m
solution works just as well.
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Container: the lemon itself.

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aWhy
usually not enough to light the LED on its own. Joining five or six of them in a chain,

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copper of one to the nail of the next, adds their pushes together, and the LED glows.

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ag a tomato or an orange, and with other pairs of
Try This: repeat it with a potato,
metals — zinc and copper, aluminium and copper, magnesium and copper. Which

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pair lights the LED most brightly?

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Activity 4.6: Let us construct — Page 56
Section 4.3.1 Voltaic cell

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ACTIVITY

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Q1 a
Connect the LED between the copper wire of the first lemon and the iron nail of the
last lemon, using connecting wires. What do you observe? Does the LED glow?

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If the.LED a g in a shaded corner of the
c is the right way round, it glows — faintly, but clearly visible
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.co


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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Why it glows: in each lemon the copper wire and the iron nail are two different
electrodes and the lemon juice is the electrolyte, so each lemon is a small Voltaic cell.
Chemical reactions at the two metals drive a current round the outside circuit, and
that current is what makes the LED glow. Joining several lemons in a chain adds their
pushes and gives enough to light the LED.

Q2 If the LED does not glow, reverse its connections. Does the LED glow now?

Yes. Turn the LED round in the circuit and it lights up.

Why the direction matters: an LED lets current pass through it in one direction
only. As you learnt earlier, current can pass through the LED only when its positive
terminal (the longer wire) is connected to the positive terminal of the battery, and its
negative terminal (the shorter wire) is connected to the negative terminal. If it was
joined the wrong way round, no current passed and there was nothing to see — the
cell was working all along.

Tip: an LED that fails to glow is therefore not proof that the lemon cell has failed.
Always try reversing the LED before deciding that your set-up does not work.

Keep the curiosity alive — Pages 58–61
End-of-chapter questions

KEEP THE CURIOSITY ALIVE

Q1 Fill in the blanks: (i) The solution used in a Voltaic cell is called ________. (ii) A current
carrying coil behaves like a _______ .

(i) The solution used in a Voltaic cell is called electrolyte.

(ii) A current carrying coil behaves like a magnet.

Page 25 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Why these are the answers:

Electrolyte — in a Voltaic cell the two electrodes are partly dipped in a liquid,
usually a weak acid or a salt solution. It is the chemical reaction between the
electrodes and this liquid that produces the electricity, and the liquid is given the
name electrolyte.
Magnet — current in the coil produces a magnetic field. The coil then deflects a
compass needle and attracts iron clips, and it has a North and a South pole,
exactly as a bar magnet does. Such a coil is called an electromagnet.

Q2 Choose the correct option: (i) Dry cells are less portable compared to Voltaic cells.
(True/False) (ii) A coil becomes an electromagnet only when electric current flows
through it. (True/False) (iii) An electromagnet, using a single cell, attracts more iron
paper clips than the same electromagnet with a battery of 2 cells. (True/False)

STATEMENT ANSWER REASON

(i) Dry cells are less portable False A dry cell has no liquid at all — its electrolyte is a thick
compared to Voltaic cells. moist paste sealed inside a zinc container. A Voltaic cell
needs an open glass or plastic container of liquid, which
can spill and must be carried upright. The dry cell is more
portable, which is exactly why it replaced the Voltaic cell
for everyday use.

(ii) A coil becomes an True The magnetism is produced by the current. Stop the
electromagnet only when current and the field disappears and the clips fall off — an
electric current flows through it. electromagnet is a temporary magnet.

(iii) An electromagnet, using a False It is the other way round. Two cells drive a larger current,
single cell, attracts more iron so the magnetic field is stronger and more clips are held. A
paper clips than the same single cell gives a small current and a weak field.
electromagnet with a battery of
2 cells.

Page 26 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Q3 An electric current flows through a nichrome wire for a short time. (i) The wire
becomes warm. (ii) A magnetic compass placed below the wire is deflected. Choose
the correct option: (a) Only (i) is correct (b) Only (ii) is correct (c) Both (i) and (ii) are
correct (d) Both (i) and (ii) are not correct

The correct option is (c) Both (i) and (ii) are correct.

Why both happen at once: a single current produces both effects at the same time
in the same wire.

Heating effect — the nichrome offers resistance to the current, so part of the
electrical energy is converted into heat and the wire becomes warm. This is
Activity 4.5.
Magnetic effect — the current also produces a magnetic field around the wire,
so a compass placed below it is deflected. This is Activity 4.1.

Neither effect switches the other off. Nichrome simply makes the heating easier to
notice, and it conducts perfectly well, so the compass deflects too.

Q4 Match the items in Column A with those in Column B. Column A: (i) Voltaic cell (ii)
Electric iron (iii) Nichrome wire (iv) Electromagnet. Column B: (a) Best suited for
electric heater (b) Works on magnetic effect of electric current (c) Works on heating
effect of electric current (d) Generates electricity by chemical reactions

COLUMN A MATCHES COLUMN B WHY

(i) Voltaic cell (d) Generates electricity Two different electrodes in an electrolyte; the
by chemical reactions reaction between them produces the current

(ii) Electric iron (c) Works on heating Its heating element gets hot as current
effect of electric passes through it, and the hot plate presses
current the clothes

(iii) Nichrome (a) Best suited for It offers high resistance, so it gives out a lot
wire electric heater of heat for a given current and can glow red
hot without melting

(iv) (b) Works on magnetic Current in the coil produces a magnetic field,
Electromagnet effect of electric so the coil behaves as a magnet
current

Page 27 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

(i) → (d) (ii) → (c) (iii) → (a) (iv) → (b)

Q5 Nichrome wire is commonly used in electrical heating devices because it (i) is a
good conductor of electricity. (ii) generates more heat for a given current. (iii) is
cheaper than copper. (iv) is an insulator of electricity.

The correct answer is (ii) generates more heat for a given current.

Why (ii) is the reason: a nichrome wire offers higher resistance than a copper wire
of the same size and length. The greater the resistance, the more of the electrical
energy is converted into heat as the current passes through. So for the same
current, nichrome gives far more heat than copper — which is exactly what a heater,
a stove or an iron needs.

OPTION VERDICT WHY

(i) is a good conductor True, but not Copper is an even better conductor, yet copper wire is not
of electricity the reason used as a heating element — precisely because it heats too
little

(ii) generates more heat Correct This is the property that makes it a heating element
for a given current

(iii) is cheaper than Not the reason Cost is not why it is chosen; it is chosen for the heat it gives
copper

(iv) is an insulator of Wrong An insulator would not let current pass at all, so no heat
electricity could be produced. Nichrome is a conductor

Q6 Electric heating devices (like an electric heater or a stove) are often considered
more convenient than traditional heating methods (like burning firewood or
charcoal). Give reason(s) to support this statement considering societal impact.

Electric heating converts electrical energy into heat inside a heating element, so nothing has to
be burnt in the room. That single difference changes a great deal for the people using it.

Page 28 of 42

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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Clean air indoors. Firewood and charcoal give smoke and soot. Breathing that smoke day
co m
after day causes coughing and lung illness, and it is the women and small children who sit
e m.
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closest to the chulha who suffer most. An electric stove produces no smoke, no soot and no

m a
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ash.

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a and that work usually falls on women and children — hours that could go to school, study or
Time saved, especially for girls. Collecting and carrying firewood takes hours every week,

m
paid work. An electric appliance needs only a switch.

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Instant and controllable heat. The heat begins the moment the switch is ON and stops

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when it is OFF, and it can be turned up or down. A wood fire has to be lit, tended and then
put out. a g
Fewer accidents. There is no open flame, no flying spark and no live coal, so there are fewer
burns and fewer house fires — a serious matter in crowded homes.
. c om
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Forests and fuel. Less firewood and charcoal means fewer trees cut, andem
no smoke released
into theooutside air either.
. c a gl
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Cleaner

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The honest other side: the electricity itself has to be generated somewhere. If it
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comes from burning coal, the pollution has only been moved away from the home to
the power station — which is whyethe
s m chapter ends by pointing to environmentally
a
a l Electric heating also needs a reliable supply, and
friendly sources of electricalgpower.
the wires, plugs and sockets must be rated for the current the appliance draws,
otherwise they overheat.
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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Q7 Look at the Fig. 4.4a.

A B

S

E W

N

magnetic compass

− +
cell
(a)

Fig. 4.4(a), page 51 — redrawn sketch: the magnetic compass placed near end A of the
electromagnet, which is connected to the cell.

If the compass placed near the coil deflects: (i) Draw an arrow on the diagram to
show the path of the electric current. (ii) Explain why the compass needle moves
when current flows. (iii) Predict what would happen to the deflection if you reverse
the battery terminals.

(i) The path of the current. In Fig. 4.4a the cell lies below the coil, with its negative terminal on
the left and its positive terminal on the right. So the current leaves the positive terminal, goes
up the right-hand wire to end B, passes through the turns of the coil from B to A, comes down
the left-hand wire and enters the negative terminal. Mark the arrows in that order all the way
round the loop.

Page 30 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

A B

compass S N

current current up
down from A to B

− +

Q7 — the current leaves the + terminal, travels up to end B, passes through the coil from B to A, and
returns to the − terminal. The red tip of the needle (its north pole) is attracted to end A, so end A is
the South pole.

(ii) Why the compass needle moves. Current going round the turns of the coil produces a
magnetic field, and the coil therefore behaves as a magnet with a North and a South pole at its
two ends. The compass needle is itself a tiny magnet. Placed in the coil's magnetic field, it is
pulled round until it lines up with that field — which is what you see as a deflection. Switch the
current off and the field disappears, so the needle goes back to north–south.
(iii) If the battery terminals are reversed. The current then goes round the coil the opposite
way, so the poles of the electromagnet swap over — end A becomes North and end B becomes
South. The needle therefore deflects in the opposite direction. The amount of deflection stays
about the same, because reversing the cell does not change how much current flows — only
which way it flows.

The idea behind it: strength depends on how much current flows (and on the
number of turns); polarity depends on which way it flows. Change the amount and
the deflection grows or shrinks; change the direction and the deflection flips.

Page 31 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Q8 Suppose Sumana forgets to move the switch of her lifting electromagnet model to
OFF position (in introduction story). After some time, the iron nail no longer picks
up the iron paper clips, but the wire wrapped around the iron nail is still warm. Why
did the lifting electromagnet stop lifting the clips? Give possible reasons.

The wire is still warm, so some current is still flowing — the circuit has not broken. What has
failed is the strength of the magnetic effect, not the circuit.
Possible reasons

1. The cell has run down — the most likely reason. Left connected for a long time, the
chemicals inside the cell get used up. The cell becomes weak, the current falls, and a small
current makes only a weak magnetic field — too weak to hold the clips against their own
weight. If it is left long enough the cell goes fully dead.
2. Heat has been building up all this while. Current has been flowing continuously through
the coil for a long time, and the heating effect works on every bit of that time. So the coil is
warm even though the current is now much smaller than it was at the start. A wire that has
been warmed for many minutes stays warm for a while.
3. A connection may have loosened. The warmth softens tape and loosens twisted joints; a
partly loose joint lets only a trickle of current through — enough to keep the wire warm, not
enough to lift clips.

The key idea: the two effects of current do not fail together. The magnetic effect
needs a reasonably large current to lift anything, while a small current flowing for a
long time is quite enough to leave a wire feeling warm. Warm wire plus clips falling
off is exactly the signature of a current that has dropped, not of a current that has
stopped.

Tip: this is why Activity 4.2 warns you not to keep the coil joined to the cell for more
than a few seconds. Switch an electromagnet OFF the moment you are not using it
— it saves the cell and keeps the coil cool.

Page 32 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Q9 In Fig. 4.12, in which case the LED will glow when the switch is closed?

Copper strip

Iron nail

Lemon juice

(a)

Copper strip

Iron nail

Pure water

(b)
Fig. 4.12, page 60 — redrawn: the same circuit of an LED, a switch and two electrodes (an
iron nail and a copper strip) dipped in (a) lemon juice and (b) pure water.

The LED glows in case (a) — the beaker containing lemon juice. In case (b), with pure water, it
does not glow.

Page 33 of 42

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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

co m
m.
CASE LIQUID IN THE BEAKER DOES IT ACT AS AN ELECTROLYTE? LED

m as e Glows
(a)
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Lemon juice Yes — it is a weak acid
a g l
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(b) No Does not glow

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Why: in each beaker there is an iron nail and a copper strip — two electrodes of
different metals. That is only half of a m .
s e Voltaic cell; the other half is the electrolyte.
a the three parts of a Voltaic cell are complete:
Lemon juice is a weak acid, so in l(a)
ag
chemical reactions take place at the two metals, a current flows round the circuit,
and the LED lights. Pure water is not an electrolyte, so in (b) no such reaction is set
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up and the water does not let current through either. Closing the switch changes
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nothing.

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s
switch again. A salt solution is an electrolyte, and the LED should now glow —
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showing that it was the liquid, not the metals, that was at fault.

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Neha keeps the coil exactly the same as in Activity 4.4 but slides the iron nail out,
co
Q10
leaving only the coiled wire. Will the coil still deflect the compass? If yes, will the
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deflection be more or less than before?

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Yes, the coil will still deflect the compass — but the deflection will be less than it was with

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the iron nail inside.
. a g
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Why it still works: the magnetic
a current is unchanged. You saw this yourself in Activity 4.3:
turns of the coil, and the

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at the stage shown in Fig. 4.3c the coil was wound on nothing but a paper cylinder,
and both compass needles were already deflected — before any nail was put in.
. co
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l a se
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out and that extra contribution is gone; only the coil's own field is left. So the needle
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still turns, but through a smaller angle — and the coil may no longer be able to hold
m .
paper clips.
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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Check it yourself: mark the resting position of the needle on a sheet of paper, then
note the deflected position with the nail in and with the nail out. The difference
between the two angles is the iron core's contribution.

Q11 We have four coils, of similar shape and size, made up from iron, copper,
aluminium, and nichrome as shown in Fig. 4.13.

Iron Copper

+ − + −

(a) (b)

Aluminium Nichrome

+ − + −

(c) (d)

Fig. 4.13, page 60 — redrawn: four identical circuits, each with a cell, a switch and a coil
of the named metal.

When current is passed through the coils, compass needles placed near the coils
will show deflection. (i) Only in circuit (a) (ii) Only in circuits (a) and (b) (iii) Only in
circuits (a), (b), and (c) (iv) In all four circuits

The correct answer is (iv) In all four circuits.

Page 35 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Why: iron, copper, aluminium and nichrome are all metals, and all four are
conductors of electricity. So when each switch is closed, current flows in every one of
the four coils — and any current carrying coil produces a magnetic field around it.
Every one of the four compasses will therefore be deflected.

COIL CONDUCTS PRODUCES A MAGNETIC COMPASS
CURRENT? FIELD? DEFLECTS?

(a) Iron Yes Yes Yes

(b) Copper Yes Yes Yes

(c) Yes Yes Yes
Aluminium

(d) Nichrome Yes Yes Yes

Did you know? The four deflections need not be equal. Nichrome offers the most
resistance, so it lets the least current through and gives the smallest deflection —
while it warms up the most. The magnetic effect is present in all four; only its size
differs.

Discover, design, and debate — Page 61
Science, Society and Interdisciplinary Projects

DISCOVER, DESIGN, AND DEBATE

Q1 Make coils of turns 25, 50, 75, and 100. Connect them to the same cell one by one.
Note the deflection in a magnetic compass placed in the same position in all the
cases. Report your observations. Draw conclusion of the effect of number of turns
of the coil on the strength of the electromagnet.

How to do it fairly. Only one thing must change from trial to trial — the number of turns.

Use the same cell, the same insulated wire and the same paper cylinder each time.
Mark the compass position on the table with chalk and never move it; keep the same
distance from the end of the coil.
Note the resting direction of the needle first, then the deflected direction, and record the
angle turned through.
Connect for only a few seconds each time, so the cell does not weaken as you go along.

Page 36 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

NUMBER OF TURNS DEFLECTION OF COMPASS NEEDLE NUMBER OF CLIPS HELD

25 Smallest Fewest

50 Larger More

75 Larger still More still

100 Largest Most

Conclusion. With the current kept the same, the strength of an electromagnet increases as the
number of turns of the coil increases.

Why it happens: each turn carries the same current and makes its own magnetic
field. Because every turn is wound in the same direction, all these fields point the
same way inside the coil and add together. More turns means more fields adding up
in the same region, so the total field is stronger.

Tip: for a fair test the coil must stay the same length as you add turns — wind the
extra turns in neat layers, not by stretching the coil out along the cylinder.

Q2 Take two thin nichrome wires of equal length and different thickness
(approximately one of these wire thickness to be double of the other, say 0.3 mm
and 0.6 mm). Connect them one by one in a circuit which has a switch and a cell,
and allow the current to flow for 30 s in each case. Momentarily touch these wires.
Which wire heats up more? Now repeat the same activity with two nichrome wires
of same diameter but of different lengths. Prepare a brief report of your activity.

Do this only under your teacher's supervision. Touch each wire momentarily, never hold it,
and switch OFF as soon as the 30 s are over.
Part 1 — same length, different thickness. The thinner (0.3 mm) wire heats up more.
Part 2 — same thickness, different length. The longer wire heats up more when the two are
compared over the same 30 seconds.

TRIAL WHAT WAS CHANGED WHICH FELT HOTTER

1 0.3 mm and 0.6 mm, same length The 0.3 mm (thinner) wire

2 Short and long, same thickness The longer wire

Page 37 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Why: the chapter tells us that the heat generated in a wire depends on the material,
thickness, length of the wire and the duration for which the current flows. A
thinner wire offers more resistance to the current than a thick one of the same
material and length, so more of the electrical energy is turned into heat in it. A
longer wire likewise offers more resistance than a short one of the same thickness.
This is why the heating element of a heater is made of a long, thin nichrome coil
rather than a short fat rod.

Writing the report. State the aim; list the materials with their exact sizes; describe what you
did; give a table of your observations; then write the conclusion in one sentence for each part
and add the precaution you followed.

Safety first: keep the current flowing for no more than the 30 s stated, and do not
touch the wire for an extended period, to avoid any injuries.

Q3 Try to make an electric cell using various fruits and vegetables. Also try with
electrodes of different metals. Prepare a brief report.

Method. Build the lemon cell of Activity 4.6 again, but change one thing at a time.

Changing the fruit or vegetable: keep the same pair of electrodes (copper wire and iron
nail) and try lemon, orange, tomato, potato, raw mango, and a cup of salt solution.
Changing the metals: keep the same lemon and try the pairs the chapter names — zinc and
copper, zinc and silver, aluminium and copper, iron and copper, magnesium and copper, lead
and copper.
Judge each by how brightly the LED glows. Use the same LED, the same number of cells in
the chain and the same spacing of the electrodes each time, otherwise the comparison
means nothing.

Page 38 of 42

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Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

co m
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WHAT YOU TRY WHAT TO REASON

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EXPECT

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e m
asraw mango, orange
Juicy, sour fruits — LED glows well Their juice is a fairly strong weak acid, so it is a good

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lemon, electrolyte

Potato, tomato LED glows, usually The juice is a weaker electrolyte, so the push produced

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more faintly is smaller

m
e A cell needs two different metals; identical rods react
Two electrodes of the
g
LED does not glow
l as
same metal a identically and no push is produced

Zinc with copper, Usually the
co m
Copper acts as the positive electrode while zinc acts as

e m.
magnesium with copper brightest the negative electrode, because of their chemical

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.co
properties

a g
a s em
a gl The idea being tested: every one of these is the same Voltaic cell — two different
electrodes and an electrolyte. By changing only the electrolyte, or only the metals,
m a s
.co agl
you find out which part decides how much electricity the cell can produce.

se m
g l a
a
Sample conclusion for your report: "A cell can be made from any juicy fruit or vegetable
provided the two electrodes are of different metals. Sour juices work better than bland ones,

m
and the zinc–copper pair gave the brightest LED. Two electrodes of the same metal never

. co
m
produced any current."

o m l a se
g one more fruit to the
.cif the LED refuses to glow, first reverse the LED, then aadd
m
asechain. Do not eat any fruit that has had metal electrodes stuck into it.
Tip:

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m . a
gl ase
Chapter at a glancea
When an electric current flows through a conductor such as a wire, it produces a magnetic
co m
m .
e
field around it. This is the magnetic effect of electric current, and it is why a compass

om g l as
.cdisappears
needle placed under a current carrying wire is deflected. Stop the current and the field

m a
se
at once.

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a
A current carrying coil that behaves as a magnet is called an electromagnet. Every turn of
the coil makes its own magnetic field, and because all the turns are wound the same way
.c
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m a
agl
these fields point the same way inside the coil and add up — so a coil of 50 turns is far

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m
stronger than a single straight wire.

l a se
An electromagnet has a North and a South pole, just like a bar magnet. Its strength is
ag the current (more cells) or the number of turns, and its poles are
increased by increasing

co m
m .
m as e
.co


a g l Page 39 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

reversed by reversing the direction of the current. It is a temporary magnet — magnetic
only while the current flows.
Most practical electromagnets carry an iron core. Iron is a magnetic material, so inside the
coil's field the iron itself becomes a magnet and its magnetism adds to the coil's. Lifting
electromagnets hung from cranes use this to pick up and drop iron and steel scrap at the
flick of a switch.
A conductor offers resistance to the flow of current, and this converts some electrical
energy into heat — the heating effect of electric current. Nichrome offers far more
resistance than copper of the same size and length, so nichrome is used as the heating
element in heaters, stoves, kettles, irons, immersion rods and hair dryers.
A Voltaic (Galvanic) cell has two electrodes of different metals dipped in an electrolyte —
a weak acid or salt solution. A chemical reaction between the electrodes and the electrolyte
produces electricity. When the chemicals are used up, the cell is dead. A lemon with a
copper wire and an iron nail is a working Voltaic cell.
A dry cell has a zinc container as the negative terminal and a central carbon rod with a
metal cap as the positive terminal, surrounded by a thick moist paste of electrolyte. A dry
cell is single use; rechargeable batteries can be charged and reused many times, but they
too wear out and must be disposed of at an e-waste facility.

Page 40 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

Quick revision

TERM WHAT IT MEANS WHERE IT EVERYDAY EXAMPLE
COMES IN THE
CHAPTER

Magnetic field The region around a magnet or a Section 4.1, page A compass needle turning
current carrying wire in which its 48 when it is brought near a
magnetic effect can be felt magnet

Magnetic effect of The production of a magnetic field Section 4.1, page The needle of a compass
electric current around a conductor when current 48 under a wire kicking the
flows through it moment the switch is closed

Electromagnet A current carrying coil that behaves Section 4.1.1, The coil in an electric bell, a
as a magnet page 50 fan, a loudspeaker

Core The iron rod or nail placed inside Section 4.1.1, The iron nail inside the coil in
the coil to make the electromagnet page 50 Activity 4.3
stronger

Poles of an The two ends, North and South, Activity 4.4, pages End A and end B of the coil in
electromagnet whose polarity reverses if the 50–51 Fig. 4.4
current is reversed

Lifting A strong electromagnet hung from Section 4.1.2, Sorting scrap iron in a scrap
electromagnet a crane, switched ON to lift and page 52 yard or a steel plant
OFF to release

Resistance The opposition a conductor offers Section 4.2, page Nichrome offers more
to the flow of electric current 53 resistance than copper of the
same size and length

Heating effect of The generation of heat in a Section 4.2, page The filament of an
electric current conductor because current is 53 incandescent lamp; a warm
flowing through it charger pin

Heating element The rod or coil of wire in an Page 53 The red-hot coil of an electric
appliance that is meant to become room heater or an electric
hot stove

Electrode One of the two metal rods, of Section 4.3.1, The copper wire and the iron
different materials, dipped in the page 55 nail in the lemon cell
electrolyte of a cell

Electrolyte The liquid or paste — usually a Section 4.3.1, Lemon juice; salt solution; the
weak acid or a salt solution — in page 55 moist paste inside a dry cell
which the electrodes are dipped

Page 41 of 42

Class 8 Science Chapter 4 Electricity: Magnetic and Heating Effects AglaSem · NCERT Solutions

TERM WHAT IT MEANS WHERE IT EVERYDAY EXAMPLE
COMES IN THE
CHAPTER

Dead cell A cell whose chemicals are used Page 55 A torch cell that no longer
up, so it can supply no more lights the lamp
electricity

Dry cell A single use cell whose electrolyte Section 4.3.2, The cell in a wall clock or a TV
is a thick moist paste, not a liquid page 57 remote

Rechargeable A battery that can be charged and Section 4.3.3, Mobile phone, laptop,
battery reused many times page 57 camera, inverter and electric
vehicle batteries

Page 42 of 42