MCQ

CLASS 12 PHYSICS

1. A force of 4N is acting between two charges in air. If the space between

them is

completely filled with glass (relative permittivity = 8), then the new force will
be

(a) 2N ( b) 5N (c) 0.5N

(d) 0.2N

2 A charge q is placed at the center of the line joining two equal charges Q.
The system

of three charges will be in equilibrium if q is equal to

(a) –Q/2 ( b) –Q/4 (c )Q/2 (d) Q/4

3 Two point charges Q and -3Q are placed some distance apart. If the
electric field at the

location of Q is E, the field at the location of -3Q is

(a) E (b) -E (c) E/3 (d) -E/3

4 An electric dipole when placed in a uniform electric field will have minimum
potential

energy, if the angle between dipole moment and electric field is

(a) Zero (b) π/ 2 (c) π/3 (d)

π

5 An electric dipole consists of two opposite charges of magnitude 1μC

separated by a

distance of 2cm. The dipole is placed in an electric filed 10-5 V/m. The
maximum torque

(a) 10-3 Nm ( b) 2 x10-13 Nm (c) 3 x10-

3N (d) 4x10-3 Nm

ASSERTION AND REASON QUESTIONS

DIRECTION: Read the two statements

Assertion (A) and Reason (R) carefully to mark the correct option out of the
options

given below:

(a) Assertion and Reason both are correct statements and Reason is correct

explanation for Assertion.

(b) Assertion and Reason both are correct statements but Reason is not
correct

explanation for Assertion.

(c) Assertion is correct statement but Reason is wrong statement.

(d) Assertion is wrong statement but Reason is correct statement

6 Assertion: No two electric lines of force can intersect each other.

Reason: Tangent at any point of electric line of force gives the direction of
electric

field

7 Assertion: Coulombs law of force is applicable for point charges at rest.

Reason: Coulombs law is a central force.

8 Assertion: Electric charge is quantized.

Reason: Charging is because of transfer of an integral number of

electrons.

9 Assertion: If there exists coulomb attraction between two bodies, both of

them may

not be charged.

Reason: In coulomb attraction two bodies are oppositely charged

10 Assertion: Surface charge density of an irregularly shaped conductor is

non uniform

Reason: Surface density defined as charge per unit area

11 An electric dipole having a dipole moment of 4 × 10-9 C m is placed in a

uniform
An electric dipole having a dipole moment of 4 × 10-9 C m is placed in a
uniform

electric field such that the dipole is in stable equilibrium. If the magnitude of
the electric

field is 3 × 103 N/C, what is the work done in rotating the dipole to a position
of unstable equilibrium?

(a) zero (b) 1.2 × 10-5 J (c) 2.4 × 10-5 J (d) - 1.2 × 10-5 J

12 An infinite line of charge has a linear charge density of 10 -7 C/m. What

will be the

magnitude of the force acting on an alpha particle placed at a distance of 4

cm from the

line of charge?

a) 14.4 × 10-15 N (b) 7.2 × 10-15 N (c) 4.5 × 104 N (d) 9 × 104 N

13 Polar molecules are the molecules :

(a)having a permanent electric dipole moment

(b)having zero dipole moment

(c)acquire a dipole moment only in the presence of electric field due to

displacement of

charges

(d)acquire a dipole moment only when magnetic field is absent

14. The angle between the electric lines of force and the equipotential
surface is

(a) 0◦ (b) 90◦ (c) 180◦ (d)45◦

15 Metal cube of side 5 cm is charged with 6μC. The surface charge density
on the cube

is

(a) 0.125×10−3Cm−2

(b)0.25×10−3Cm−2
(c)4×10−3Cm−2

(d)0.4×1−3 Cm−2

16 According to Gauss law of electrostatics, electric flux through a closed

surface

depends on :

(a)the area of the surface

(b)the quantity of charges enclosed by the surface

(c) the shape of the surface

(d)the volume enclosed by the surface

17 σ is the uniform surface charge density of a thin spherical shell of radius

R. The electric

field at any point on the surface of the spherical shell is :

(a) σ/εoR (b) σ/∈o (c) σ/2εo (d)

2σ/∈o

18 A uniform electric field E= 2X103 N/C is acting along the positive x axis.
The flux in

(NC-1m2) of this field through a square of 10cm on a side whose plane is

parallel to

the y-z plane is

(a) 20 (b) 30 (c) 10

(d) 40

19 An electric dipole is placed at an angle of 30◦ with an electric field of

intensity 2x105N/C.

It experiences a torque equal to 4Nm.The charge on the diploe length is 2cm

is

(a) 8 mC (b) 4 m C (c ) 6 mC (d) 2 mC

20 A metal cube of side 5cm is charged with 6 μC. The surface charge
density of the

cube is

(a) 0.125x10-3Cm-2
(b)0.25x10-3Cm-2

(c )4x10-3Cm-2

(d)0.4x10-3Cm-2

21 The electric field due to a short electric dipole at a large distance (r) from
center of

dipole on the equatorial plane varies with distance as

(a) r (b) 1/r (c) 1/r3 d) 1/r2

ELECTRIC POTENTIAL AND CURRENT ELECTRICITY

Q1. If voltage applied on a capacitor is increased from V to 2V, choose the

correct conclusion.

(a) Q remains the same, C is doubled

(b) Q is doubled, C doubled

(c) C remains same, Q doubled

(d) Both Q and C remain same

Q2. A parallel plate capacitor is charged. If the plates are pulled apart

(a) The capacitance increases

(b) The potential differences increase

(c) The total charge increases

(d) The charge & potential difference remain the same

Q3. Which of the following is an example of a molecule whose centre of mass

of positive and negative charges coincide each other?

(a)CO2 (b) CO (c) CH3OH (d) NH3

Q4.Capacitors A and B are identical. Capacitor A is charged so it stores 4 J of

energy and capacitor B is uncharged. The capacitors are then connected in
parallel. The total stored energy in the capacitors is now:

a) 16 J b) 8 J c) 4 J d) 2 J
 Q5.If both the plate area and the plate separation of a parallel-plate
capacitor are doubled, the capacitance is:

a) doubled b) halved c) unchanged d)

tripled

Q6.An electric dipole of dipole moment p is placed in a uniform electric field

of strength E in a direction perpendicular to the field. The work done in
rotating the dipole by an angle 900 without acceleration in a plane
perpendicular to the field is:

a) pE b) –pE c). Zero d). -2pE

Q7.A small metallic ball having charge q is placed inside an insulated box.
The insulated box is then placed inside a metallic box. The net charge
enclosed inside the metallic box is: a) Zero b) q c)–q
d) 2q

Q8.In a parallel plate capacitor, the capacity increases if

(a) area of the plate is decreased. (b) distance between the plates
increases.

(c) area of the plate is increased. (d) dielectric constantly decreases.

a) If both Assertion and Reason are true and Reason is correct explanation of
Assertion.

b) If both Assertion and Reason are true but Reason is not the correct
explanation of assertion

c) If Assertion is true but Reason is false.

d) If both Assertion and Reason are false

9.Assertion(A): A current flows in a conductor only when there ia an electric

field within the conductor

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

decreases.

10.Assertion(A): An electric bulb starts glowing instantly as it is switched on.

Reason(R): Drift speed of electrons in a metallic wire is very large.

11.Assertion(A): A wire carrying an electric current has no electric field
around it.

Reason(R): Rate of flow of electrons in one direction is equal to the rate of

flow of protons in opposite direction.

12.Assertion(A): Though large number of free electrons are present in the

metal. Yet there is no current in the absence of electric field.

Reason(R): In the absence of electric field electrons move randomly in all

directions. 13.Assertion(A): The value of temperature coefficient of
resistance is positive for metals.

Reason(R): The temperature coefficient is resistance for insulator is also

positive.