electrostatics mock test,NCERT Class 12 Physics Objective Questions

Electrostatics Mock Test-1

Questions No:1

When 1014 electrons are removed from a neutral metal sphere, the charge on the sphere becomes

[A] 16µC

[B] -16µC

[C] 32 µ C

[D] -32µC

Questions No:2

A conductor has 4×10-19 C positive charge. The conductor has (charge on electron = 6 x 10-19 C)

[A] 9 electrons in excess

[B] 27 electrons in short

[C] 27 electrons in excess

[D] 9 electrons in short

Questions No:3

Charge on α particle is

[A] 4.8 x 10-19 C

[B] 16×10-19 C

[C] 3.2×10 -19C

[D] 6.4x 10 -19C

Questions No:4

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

Questions No:5

When a body is earth connected, electrons from the earth flow into the body. This means the body is

[A] uncharged

[B] charged positively

[C] charged negatively

[D] an insulator

Questions No:6

There are two charges +1µC and +5µC. The ratio of the forces acting on them will be

[A] 1:5

[B] 1:1

[C] 5:1

[D] 1:25

Questions No:7

Fg and Fe represents gravitational and electrostatic force respectively between electrons situated at a distance 10 cm. The ratio of\( \frac{F_g}{F_e} \)is of the order of

[A] 1042

[B] 10-21

[C] 1024

[D] 10-43

Questions No:8

Two similar small spheres having +q and -q charge are kept at a certain distance. F force acts between the two. If in the middle of two spheres, another similar small sphere having +q charge is kept, then it will experience 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

Questions No:9

The force between two charges 06 m apart is 5 N. If each charge is moved towards the other by 01 m, then the force between them will become

[A] 7.2 N

[B] 11.25 N

[C] 22.5 N

[D] 45 N

Questions No:10

Two charged spheres separated at a distance d exert a force F on each other. If they are immersed in a liquid of dielectric constant 2, then what is the force (if all conditions are same)

[A] \(\frac{F}{2}\)

[B] F

[C] 2F

[D] 4F

Questions No:11

Electric charges of 1 µC, -1 µ C and 2 µC are placed in air at the corners A, B and C respectively of an equilateral triangle ABC having length of each side 10 cm. The resultant force on the charge at C is

[A] 0.9N

[B] 1.8N

[C] 2.7 N

[D] 3.6N

Questions No:12

Two small conducting spheres of equal radius have charges +10µ C and -20µ C respectively and placed at a distance R from each other. They experience force F1. If they are brought in contact and separated to the same distance, they experience force F2. The ratio of \( \frac{F_1}{F_2} \) is

[A] 1:8

[B] -8:1

[C] 1:2

[D] -2 :1

Questions No:13

Equal charges q are placed at the four corners A, B, C and D of a square of length a. The magnitude of the force on the charge at B will be

[A] \( \frac {3q^2}{4πε_0a^2}\)

[B] \( \frac {q^2}{4πε_0a^2}\)

[C] \( (\frac {1+2\sqrt{2}}{2} )\) \( \frac {3q^2}{4πε_0a^2}\)

[D] \( ( 2+ \frac {1}{\sqrt2} ) \) \( \frac {3q^2}{4πε_0a^2}\)

Questions No:14

Two equally charged, identical metal spheres A and B repel each other with a force F. The spheres are kept fixed with a distance r between them. A third identical, but uncharged sphere C is brought in contact with A and then placed at the mid-point of the line joining A and B. The magnitude of the net electric force on C is

[A] F

[B] \( \frac{F}{4} \)

[C] \( \frac{F}{2} \)

[D] 4F

Questions No:15

Two charges +4e and +e are at a distance x apart. At what distance, a charge q must be placed from charge + e, so that it is in equilibrium?

[A] \( \frac{x}{2} \)

[B] \( \frac{2x}{3}\)

[C] \(\frac{x}{3} \)

[D] \(\frac{x}{4} \)

Questions No:16

A charge Q is placed at each of the two opposite corners of a square. A charge q is placed at each of the other two corners. If the resultant force on Q is zero, then

[A] Q =\( \sqrt{2}q \)

[B] Q = -\( \sqrt{2}q \)

[C] Q = \(2\sqrt{2}q \)

[D] Q = -\(2\sqrt{2}q \)

Questions No:17

A charge q is lying at mid-point of the line joining the two similar charges Q. The system will be in equilibrium if the value of q is

[A] \( \frac{Q}{2}\)

[B] \(- \frac{Q}{2} \)

[C] \( \frac{Q}{4} \)

[D] \(-\frac{Q}{4}\)

Questions No:18

Two point charges +2 C and +6 C repel each other with a force of 12 N. If a charge of – 4 C is given to each of these charges, the force now is

[A] 4 N (repulsive)

[B] 4 N (attractive)

[C] 12 N (attractive)

[D] d) 8 N (repulsive)

Questions No:19

A charge \( q_1 \) exerts some force on a second charge \( q_2 \). If a third charge \( q_3 \) is brought near \( q_2 \), the force exerted by \( q_1 \) on \( q_2 \)

[A] decreases

[B] increases

[C] remains the same

[D] increases if q3 is of same sign as q1, and decreases if q3 is of opposite sign as q1

Questions No:20

Three equal charges are placed on the three corners of a square. If the force between \( q_1 \) and \( q_2 \) is \( F_{12} \) and that between q1 and q3 is \( F_{13} \), then the ratio of magnitudes \( \frac{F_{12}}{F_{13}} \)is

[A] \( \frac{1}{2} \)

[B] 2

[C] \( \frac{1}{\sqrt{2}} \)

[D] \( \sqrt2 \)