CBSE Class 12 Physics Objective Type Questions & Answers

21 Equipotentials at a great distance from a collection of charges whose total sum is not zero are approximately [NCERT Exemplar]

A spheres

B ellipsoids

C planes

D paraboloids

View Answer

Answer: spheres

22 Two small spheres each carrying a charge q are placed r metre apart. If one of the spheres is taken around the other one in a circular path of radius r, the work done will be equal to

A force between them/2πr

B zero

C force between them × 2πr

D force between them × r

View Answer

Answer: zero

23 The electric potential V at any point O (x, y, z all in metres) in space is given by V = 4x² volt. The electric field at the point (1 m, 0, 2 m) in volt/metre is

A 16 along positive z-axis

B 8 along negative x-axis

C 8 along positive x-axis

D 16 along negative x-axis

View Answer

Answer: 8 along negative x-axis

24 If a unit positive charge is taken from one point to another over an equipotential surface, then

A no work is done.

B work done is constant.

C work is done on the charge.

D work is done by the charge.

View Answer

Answer: no work is done.

25 A hollow metal sphere of radius 5 cm is charged so that the potential on its surface is 10 V. The potential at the centre of the sphere is

A 0 V

B 10 V

C Same as at point 5 cm away from the surface

D Same as at point 25 cm away from the surface

View Answer

Answer: 10 V

26 The electrostatic force between the metal plates of an isolated parallel plate capacitor C having a charge Q and area A, is

A proportional to the square root of the distance between the plates.

B linearly proportional to the distance between the plates.

C independent of the distance between the plates.

D inversely proportional to the distance between the plates.

View Answer

Answer: independent of the distance between the plates.

27 A capacitor is charged by a battery. The battery is removed and another identical uncharged capacitor is connected in parallel. The total electrostatic energy of resulting system

A decreases by a factor of 2.

B remains the same.

C increases by a factor of 4.

D increases by a factor of 2.

View Answer

Answer: decreases by a factor of 2.

28 A conductor with a positive charge

A may be at +ve, zero or -ve potential.

B is always at negative potential.

C is always at +ve potential.

D is always at zero potential.

View Answer

Answer: may be at +ve, zero or -ve potential.

29 Which of the following options are correct? If a conductor has a potential V 4- 0 and there are no charges anywhere else outside, then [NCERT Exemplar]

A there must not be charges on the surface or inside itself.

B there cannot be any charge in the body of the conductor.

C there must be charges only on the surface.

D there must be charges inside the surface.

View Answer

Answer: there cannot be any charge in the body of the conductor.

30 Which of the following options is correct? In a region of constant potential [NCERT Exemplar]

A the electric field is zero.

B there can be charge inside the regiofi.

C the electric field is uniform.

D the electric field shall necessarily change if a charge is placed outside the region.

View Answer

Answer: the electric field is zero.

31 64 drops each having the capacity C and potential V are combined to form a big drop. If the charge on the small drop is q, then the charge on the big drop will be

A 64q

B 16q

C 2q

D 4q

View Answer

Answer: 64q

32 The radii of two metallic spheres A and B are r1 and r2 respectively (r1 > r2). They are connected by a thin wire and the system is given a certain charge. The charge will be greater

A on the surface of the sphere A.

B on the surface of the sphere B.

C equal on both.

D zero on both.

View Answer

Answer: on the surface of the sphere A.

33 In parallel combination of n cells, we obtain

A more voltage

B more current

C less voltage

D less current

View Answer

Answer: more current

34 Combine three resistors 5 Q, 4.5 Q and 3 Q in such a way that the total resistance of this combination is maximum

A 12.5 Q

B 13.5 Q

C 14.5 Q

D 16.5 Q

View Answer

Answer: 12.5 Q

35 In the series combination of two or more than two resistances

A the voltage through each resistance is same.

B the current through each resistance is same.

C neither current nor voltage through each re-sistance is same.

D both current and voltage through each resis¬tance are same.

View Answer

Answer: the current through each resistance is same.

36 An electric heater is connected to the voltage supply. After few seconds, current gets its steady value then its initial current will be

A slightly higher than its steady current

B slightly less than its steady current

C equal to its steady current

D zero

View Answer

Answer: slightly higher than its steady current

37 The resistivity of alloy manganin is

A Nearly independent of temperature

B Increases rapidly with increase in temperature

C Decreases with increase in temperature

D Increases rapidly with decrease in temperature

View Answer

Answer: Nearly independent of temperature

38 A charge is moving across a junction, then

A momentum will be conserved.

B momentum will not be conserved.

C at some places momenturii will be conserved and at some other places momentum will not be conserved.

D none of these.

View Answer

Answer: none of these.

39 When there is an electric current through a conducting wire along its length, then an electric field must exist

A outside the wire but normal to it.

B outside the wire but parallel to it.

C inside the wire but parallel to it.

D inside the wire but normal to it.

View Answer

Answer: inside the wire but parallel to it.

40 A Daniel cell is balanced on 125 cm length of a potentiometer wire. Now the cell is short-circuited by a resistance 2 ohm and the balance is obtained at 100 cm. The internal resistance of the Daniel cell is

A 4/5 ohm

B 0.5 ohm

C 1.5 ohm

D None of these

View Answer