Electric charges and fields class 12 MCQ pdf

1. When a glass rod is rubbed with silk, it

(a) gains electrons from silk.

(b) gives electrons to silk.

(c) gains protons from silk.

(d) gives protons to silk.

Ans: b

2.  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.

Ans: C

3. 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

Ans:a

4.  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

Ans:c

5. 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

Ans: a

6. 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.

Ans:c

7. 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

Ans:b

8.  Which of the following statement is correct? The electric field at a point is 

(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.

Ans:d

9. 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.

Ans: a

10. 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.

Ans:b

11. SI unit of permittivity of free space is

(a) Farad

(b) Weber

(c) C2N-1 m-2

(d) C2N-1 m-2

Ans: c

12. A charge Q is placed at the centre of the line joining two point charges +q and +q as shown in the figure. The ratio of charges Q and q is

(a) 4

(b) 1/4

(c) -4

(d) -¼

Ans: d

13. The force per unit charge is known as

(a) electric flux

(b) electric field

(c) electric potential

(d) electric current

Ans: b

14. Electric field lines provide information about

(a) field strength

(b) direction

(c) nature of charge

(d) all of these

Ans:d

15. The SI unit of electric flux is

(a) N C-1 m-2

(b) N C m-2

(c) N C-2 m2

(d) N C-1 m2

Ans:d

16. The unit of electric dipole moment is

(a) newton

(b) coulomb

(c) farad

(d) debye

Ans:d

17. The surface considered for Gauss’s law is called

(a) Closed surface

(b) Spherical surface

(c) Gaussian surface

(d) Plane surface

Ans:c

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

(a) zero

(b) along the diagonal AC

(c) along the diagonal BD

(d) perpendicular to side AB

Ans:c

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