Class 12 Physics Electric Charges and Fields MCQs

1 1 V equals to:

A 1 J

B 1 JC^-1

C 1 CJ^-1

D 1 JC

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Answer:1 JC^-1

2 When a dipole of moment

A

B

C

D

View Answer

Answer:

3 A semicircular arc of radius r is charged uniformly and the charge per unit length is λ. The electric field at the centre is:

A

B

C

D

View Answer

Answer:

4 Four charges are arranged at the comers of a square ABCD, as shown. The force on the charge kept at the centre O is

Electric Charges and Fields

A zero

B along the diagonal AC

C along the diagonal BD

D perpendicular to side AB

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Answer:along the diagonal BD

5 Which of the following statements is not true about Gauss’s law?

A Gauss’s law is true for any closed surface.

B The term q on the right side side of Gauss’s law includes the sum of all charges enclosed by the surface.

C Gauss’s law is not much useful in calculating electrostatic field when the system has some symmetry.

D Gauss’s law is based on the inverse square dependence on distance contained in the coulomb’s law

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Answer:Gauss’s law is not much useful in calculating electrostatic field when the system has some symmetry.

6 Gauss’s law will be invalid if

A there is magnetic monopoles.

B the inverse square law is not exactly true.

C the velocity of light is not a universal constant.

D none of these.

View Answer

Answer:the inverse square law is not exactly true.

7 A point charge +q is placed at a distance d from an isolated conducting plane. The field at a point P on the other side of the plane is

A directed perpendicular to the plane and away from the plane.

B directed perpendicular to the plane but towards the plane.

C directed radially away from the point charge.

D directed radially towards the point charge.

View Answer

Answer:directed perpendicular to the plane and away from the plane.

8 Which of the following statement is correct? The electric field at a point is [NCERT Exemplar]

A always continuous.

B continuous if there is a charge at that point.

C discontinuous only if there is a negative charge at that point.

D discontinuous if there is a charge at that point.

View Answer

Answer:discontinuous if there is a charge at that point.

9 In Fig. (i) two positive charges q₂ and q₃ fixed along the y-axis, exert a net electric force in the +x direction on a charge q₁ fixed along the x-axis. If a positive charge Q is added at (x, 0) in figure (ii), the force on q₁ is

Electric Charges and Fields

A shall increase along the positive x-axis.

B shall decrease along the positive x-axis.

C shall point along the negative x-axis.

D shall increase but the direction changes because of the intersection of Q with q2 and qy

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Answer:shall increase along the positive x-axis.

10 The magnitude of electric field intensity E is such that, an electron placed in it would experience an electrical force equal to its weight is given by

A mge

B mg/e

C e/mg

D e²g/m²

View Answer

Answer:mg/e

11 A point charge q is placed at a distance a/2 directly above the centre of a square of side a. The electric flux through the square is

A

B

C

D

View Answer

Answer:

12 The electric field intensity due to an infinite cylinder of radius R and having charge q per unit length at a distance rir r(r > R) from its axis is

A directly proportional to r².

B directly proportional to r³.

C inversely proportional to r.

D inversely proportional to r².

View Answer

Answer:inversely proportional to r.

13 Total electric flux coming out of a unit positive charge kept in air is

A ε₀

B

C (4πε₀)^-1

D 4πε₀

View Answer

Answer:

14 An electric charge q is placed at the centre of a cube of side a. The electric flux on one of its faces will be

A

B

C

D

View Answer

Answer:

15 Electric field at a point varies as r° for

A an electric dipole

B a point charge

C a plane infinite sheet of charge

D a line charge of infinite length

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Answer:a plane infinite sheet of charge

16 A cylinder of radius R and length L is placed in a uniform electric field E parallel to the cylinder axis. The total flux for the surface of the cylinder is given by

A

B

C

D Zero

View Answer

Answer:Zero

17 The electric field inside a spherical shell of uniform surface charge density is

A zero.

B constant, less than zero.

C directly proportional to the distance from the centre.

D none of the these

View Answer

Answer:zero.

18 Two charges of equal magnitudes kept at a distance r exert a force F on each other. If the charges are halved and distance between them is doubled, then the new force acting on each charge is

A F/8

B F/4

C 4F

D F/16

View Answer

Answer: F/16

19 A charge Q is divided into two parts of q and Q – q. If the coulomb repulsion between them when they are separated is to be maximum, the ratio of Q/q should be

A 2:1

B 1/2

C 4:1

D 1/4

View Answer

Answer:2:1

20 Two similar spheres having +Q and -Q charges are kept at a certain distance. F force acts between the two. If at the middle of two spheres, another similar sphere having +Q charge is kept, then it experiences a force in magnitude and direction as

A zero having no direction.

B 8F towards +Q charge.

C 8F towards -Q charge.

D 4F towards +Q charge.

View Answer