Class 12 PT I Question Paper 2024-25 Physics

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Question Paper for CBSE Board, KV Schools,
State Board following NCERT Syllabus

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Question Paper based on NCERT Syllabus
CBSE Board Question Paper / KV Schools Question Paper
Class – XII Unit Test – 1
Time – 90 minutes Subject – Physics M.M. – 40
Section – A (1 Mark Each)
Q.1) Two point charges +4 μC and +1 μC are separated by our distance of 2 m in air . The point on the line joining
charges at which the net electric field of the system is zero –

(a) 4 m (b) 3 m (c) 4/3 m (d) 3/4 m

Q.2) If an electric dipole is placed in a non-uniform electric field, it experiences –

(a) a force but not a torque (b) a torque but not a force

(c) always a force and a torque (d) neither a force nor a torque

Q.3) In air the value of the total electric flux emitted from unit positive charge is –

(a) ε₀ (b) 1/ ε₀ (c) 4πε₀ (d) 1/4πε₀

Q.4) A force of 2.25 N acts on a charge of 15 × 10⁻⁴ C . The intensity of electric field at that point is –

(a) 1.5 N/C (b) 15 N/C (c) 150 N/C (d) 1500 N/C

Q.5) Net capacitance of three identical capacitors in series is 1 μF and in parallel is 9 μF . The ratio of energy stored in
the two configurations if they are both connected to the same source is –

(a) 1 : 9 (b) 9 : 1 (c) 1 : 3 (d) 3 : 1

Q.6) The capacitance of a parallel plate capacitor depends upon which of the following factors ?

(a) area of the plates (b) distance between the plates

(c) permittivity of the medium between the plates (d) all of the above

Q.7) What is the angle between electric field and equipotential surface ?

(a) 0° always (b) 90° always (c) 0° to 90° (d) 0° to 180°

Q.8) Three capacitors of capacitances 2 μF , 3 μF and 6 μF are joined in series with each other. The equivalent
capacitance is –

(a) 1/2 μF (b) 1 μF (c) 2 μF (d) 11 μF

Q.9) If there are n capacitors in parallel connected to V volt source, then the energy stored is equal to -

(a) CV (b) CV² (c) nCV² / 2 (d) CV² / 2n

Q.10) The resistance of a metal wire increases with increasing temperature on account of –

(a) decrease in free electron density (b) decrease in relaxation time

(c) increase in free electron density (d) increase in relaxation time

Q.11) The resistivity of metal is decreases if –

(a) temperature increases (b) temperature decreases (c) temperature remains constant (d) none of these

Q.12) The electric power consumed by a 200 V – 100 W bulb when operated at 110 V is –

(a) 26 W (b) 30 W (c) 35 W (d) 15 W

Q.13) A battery of EMF ‘ ε ‘ and internal resistance ‘ r ‘ gives a current of 0.5 A with an external resistor of 12 ohm and a
current of 0.25 A with an external resistor of 25 ohm. The EMF of the cell is -

(a) 1.5 V (b) 3.5 V (c) 4.5 V (d) 6.5 V

Q.14) Three identical cells each of emf 2 V and unknown internal resistance are connected in parallel. This combination
is connected to a 5 Ω resistor. If the terminal voltage across the cells is 1.5 V , then the internal resistance of each cell is –

(a) 2 Ω (b) 3 Ω (c) 4 Ω (d) 5 Ω

Assertion – Reason Type Questions
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
(b) Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
(c) Assertion (A) is true but Reason (R) is false.
(d) Both Assertion (A) and Reason (R) are false.

Q.15) Assertion (A) : Net electric field inside a conductor is zero.

Reason (R) : Total positive charge equals to total negative charge in a charged conductor.

Q.16) Assertion (A) : A current flows in a conductor only when there is an electric field within the conductor.

Reason (R) : The drift velocity of electrons in presence of electric field decreases.

Section – B (2 Marks Each)
Q.17) Define equipotential surface . Draw the equipotential surfaces due to an electric dipole .

Q.18) Deduce the relation between current flowing through a conductor and drift velocity of free electrons .

Section – C (3 Marks Each)
Q.19) What is an electric dipole? Derive an expression for the torque experienced by an electric dipole of dipole moment
p in a uniform electric field E .

Q.20) Define the capacitance of a capacitor. Obtain the expression for the capacitance of a parallel plate capacitor in
vacuum in terms of plate area A and seperation d between the plates.
Or
Derive an expression for the potential energy of an electric dipole of dipole moment p in an electric field E .
Section – D (5 Marks Each)
Q.21) State Gauss's law in electrostatics. Derive an expression for the electric field due to an infinitely long straight
uniformly charged wire. Also draw the graph between E and r .
Q.22) State the two laws of Kirchhoff’s . Two cells of emfs 1.5 V and 2.0 V and internal resistance 1 ohm and 2 ohm
respectively are connected in parallel so as to send current in the same direction through an external resistance of 5
ohm.

(i) Draw the circuit diagram.

(ii) Using Kirchhoff’s laws, calculate

(a) Current through each branch of the circuit.
(b) Potential difference across the 5 ohm resistance.

Section – E (4 Mark)
Case Study (Effect Of Dielectric On Capacitance)
The capacitance of parallel plate capacitors is modified when a dielectric is present . The dielectric constant of a
substance is the factor by which the capacitance increases from its vacuum value, when the dielectric is inserted fully
between the plates of a capacitor.

Q.23) Read the above paragraph carefully and answer the following questions.

a) In a parallel plate capacitor, the capacitance increases from 4 microfarad to 80 microfarad on introducing a
dielectric medium between the plates. What is the dielectric constant of the medium?
b) What is the value of dielectric constant for metal ?
c) A slab of material of dielectric constant K has the same area as the plates of a parallel-plate capacitor but has a
thickness (3/4) d , where d is the seperation of the plates. How is the capacitance changed when the slab is
inserted between the plates ?

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