Goa Board Class 12 Question Paper 2024 Physics

2024 III 04 0930 Seat No.

Time : 3 Hours PHYSICS
Subject Code

H 4 7 0 2
Total No. of Questions : 35 (Printed Pages : 12) Maximum Marks : 70

INSTRUCTIONS : (i) All questions are compulsory.
(ii) This question paper has four sections.
(iii) Section A contains 14 questions of one mark each.
Section B contains 10 questions of two marks each.
Section C contains 8 questions of three marks each.
Section D contains 3 questions of four marks each.
(iv) There is no overall choice. However, internal choices
have been provided in one question of three marks and
three questions of four marks weightage. You have to
attempt only one of the choices in such questions.
(v) Use of calculators is not permitted. However, you may
ask for mathematical tables.
(vi) You may use the following values of physical constants
wherever necessary :
h = 6.63 × 10–34 Js
= 3.14
e = 1.6 × 10–19 C
c = 3 × 108 ms–1

0
= 8.854 × 10–12 C2 N–1 m–2
1
= 9 × 109 Nm2 C–2
4 0

µ0 = 4 × 10–7 TmA–1
me = 9.1 × 10–31 kg

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Section A
Directions for Q.1–Q.7 :
Select and write the most appropriate options from those given below each
question.
1. Rutherford’s alpha particle scattering experiment was responsible for the
discovery of : 1
• Nucleus
• Electron
• Helium
• Neutrino
2. Which of the following gives the polarity of the induced emf ? 1
• Biot-Savart Law
• Lenz’s Law
• Ampere’s circuital law
• Fleming’s right hand rule
3. In AC generator, if the rotational velocity of armature is doubled, the induced
emf will : 1
• become half
• become double
• become zero
• remains unchanged

4. The oscillating electric and magnetic field vectors of an electromagnetic wave
are oriented along : 1
• the same direction but differ in phase by 90º
• the same direction and are in phase
• mutually perpendicular direction and are in phase
• mutually perpendicular direction and differ in phase by 90º

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5. The generation of energy in the sun is mainly due to : 1

• Fission of heavy nuclei

• Fission of light nuclei

• Fusion of heavy nuclei

• Fusion of light nuclei

6. The frequencies of X-rays, gamma rays and ultra violet rays are a, b and c
respectively, then : 1

• a < b, b > c

• a > b, b < c

• a > b, b > c

• a < b, b < c

7. A lens of power +2 dioptre is placed in contact with a lens of power
–1 dioptre. The combination will behave like : 1

• A convergent lens of focal length 50 cm

• A divergent lens of focal length 100 cm

• A convergent lens of focal length 100 cm

• A convergent lens of focal length 200 cm

Direction for Q.8–Q.14

Answer the following :

8. Why microwaves are considered suitable for radar systems used in aircraft
navigation ? 1

9. What is Bohr’s quantisation condition for the angular momentum of an
electron in the second orbit ? 1

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10. Why is it necessary to introduce a cylindrical soft iron core inside the coil

of a galvanometer ? 1

11. Why do we prefer steel for making permanent magnets ? 1

12. If the horizontal and vertical components of earth’s magnetic field are equal

at a place, find the angle of dip. 1

13. What is the ratio of de-Broglie wavelength associated with two electron

beams A and B accelerated through 25 V and 36 V respectively ? 1

14. In an ideal transformer, number of turns in the primary and secondary are

200 and 1000 respectively. If the input voltage is 200 V, what will be its

output voltage ? 1

Section B

15. Graph shows the variation of stopping potential (Vo) with frequency (v) for

two photosensitive metals ‘R’ and ‘S’. 2

(i) Which metal has smaller threshold wavelength ?

(ii) The distance between the light source and metal is doubled, how will

the stopping potential change ?

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16. A nucleus mn X emits one alpha particle and one positron. What will be the

mass number and atomic number of the product nucleus ? 2

17. Calculate the shortest wavelength present in the Balmer series of spectral

line. (R = 1.097 × 10–7 m–1) 2

18. A spherical shell of radius 8 cm has a charge of 1.6 × 10 –7 C, distributed

uniformly over its surface. What is the electric field at a point 12 cm from

the center of the shell ? 2

19. A coil ‘S’ is connected to low voltage bulb ‘B’ and placed near coil ‘P’ as shown

in figure : 2

(i) Give reason why the bulb lights up.

(ii) Bulb gets dimmer if the coil ‘S’ is moved slowly toward left.

20. A metallic spherical shell is charged to potential +50 V : 2

(i) What is the potential difference between points A and B ?

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(ii) Why is the electric field always perpendicular to the surface of the
charged conductor ?

21. Two bars ‘L’ and ‘M’ are made from different materials are placed in a
non-uniform magnetic field. Bar ‘L’ tends to move slightly from weaker to
the stronger field region, while bar ‘M’ tends to move from stronger to weaker
field region. What is the nature of the magnetic materials used for making
of these two bars ? What is their susceptibility ? 2

22. A rectangular current carrying loop EFGH (parallel to the plane of the paper)
is kept in a uniform magnetic field as shown in figure : 2

(i) What is the direction of the magnetic moment of the current loop ?

(ii) When is the torque acting on the loop zero ?

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23. Using Huygen's principle, derive the laws of refraction for a plane wave
propagating from a rarer to denser medium. Draw the necessary ray
diagram. 2

24. Find the effective resistance of the network shown below between the points
A and B when the switch is open and closed. 2

Section C

25.

(i) Identify the above circuit. 3

(ii) Which property of the diode is utilized in working of the above
circuit ?

(iii) Draw input and output waveforms for above circuit.

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26. In Young’s double slit experiment : 3

(i) What is the effect on the fringe width if the separation between the
slits is increased ?

(ii) What is the path difference, when two light waves coming from two
slits form third minimum ?

(iii) Why steady interference pattern is not observed when two slits are
illuminated with two separate sources ?

27. An object placed 12 cm to the left of a diverging lens of focal length –6 cm.
A converging lens with focal length of 12 cm is placed at a distance ‘d’ to
the right of the diverging lens. Find the distance ‘d’ that corresponds to a
final image at infinity. 3

28. In a potentiometer circuit shown, the balance point is at X. Towards which
end, A or B the balance point will shift when : 3

(i) Resistance ‘R’ is increased, keeping all parameters unchanged.

(ii) Resistance ‘S’ is increased keeping ‘R’ constant.

(iii) Cell ‘P’ is replaced by another cell whose emf is lower than that of
cell ‘Q’.

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29. Two slabs ‘A’ and ‘B’ made of certain material is placed inside a region of
a uniform electric field Eo as shown in figure. 3
(i) Identify nature of the slabs ‘A’ and ‘B’.
(ii) What is the total electric dipole moment of the slab ‘B’ in the absence
of external field ?

30. In a meter bridge experiment, resistances 5 and R are connected in the
left and right gap respectively. The balance point is obtained at a distance
l1 from A as shown in figure. When the resistance ‘R’ is shunted with equal
resistance, the new balance point is at 1.6 l1. Calculate the value resistance
R and length l1. 3

A l1 100 – l1 C

Metre scale

K3

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31. With the help of neat diagram, derive an expression for the electric field at
any point on the equatorial line of an electric dipole. 3

32. Derive an expression for the magnetic field due to a circular current carrying
loop, at a point along its axis. Draw the necessary diagram. 3

Or

Show that the force per unit length between two parallel current carrying
wires is inversely proportional to the distance between them. Draw the
necessary diagram. 3
Section D

33. Identify the logic gates marked P and Q. Rewrite the truth table with output
Y for input conditions shown in the truth table for the combination of logic
gates and identify the logic operation carried out by the combination of
gates. 4

A B Y

0 0

0 1

1 0

1 1

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Or

A semiconductor X is made by doping a germanium crystal with indium.

A second semiconductor Y is made by doping germanium with arsenic. The

two are joined end to end and connected to a battery as shown : 4

(i) Identify the semiconductors X and Y obtained after doping.

(ii) Identify the biasing and draw VI characteristics.

(iii) If the polarity of the source is reversed, how will the width of the

depletion region change ?

34. Derive an expression for the ac current, when an ac source is applied across
a pure inductor. Draw the necessary phasor diagram. 4

What is the average power supplied to an inductor over one complete cycle
of the ac source ?

Or

Derive an expression for the ac current, when an ac source is applied across
a pure capacitor. Draw the necessary phasor diagram.

What is the average power supplied to a capacitor over one complete cycle
of the ac source ? 4

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35. With the help of a neat ray diagram, derive an expression for the refractive

index of the material of a prism. Hence obtain the angle of minimum

deviation of a thin prism. 4

Or

With the help of a neat ray diagram, derive the relationship between the

object distance, image distance and focal length of a concave mirror. Also

deduce the formula for linear magnification. 4

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