Electrostatics Mock Test-3

Questions No:1

Two equal positive charges are kept at points A and B. The electric potential at the points between A and B (excluding these points) is studied while moving from A to B. The potential

[A] continuously increases

[B] continuously decreases

[C] increases then decreases

[D] decreases then increases



Questions No:2

A uniform electric field having a magnitude E0 and direction along the positive X-axis exists. If the potential Vis zero at x = 0, then its value at X = + x will be

[A] +xE0

[B] -xE0

[C] +\(x^2\)E0

[D] –\(x^2\)E0



Questions No:3

A charge of 5 C experiences a force of 5000 N when it is kept in a uniform electric field. What is the potential difference between two points separated by a distance of 1 cm?

[A] 10 V

[B] 250V

[C] 1000 V

[D] 2500V



Questions No:4

The electric potential V is given as a function of distance x (metre) by V = (5x2 +10x -9) volt. Value of electric field at x = 1 is

[A] – 20 V/m

[B] 6 V/m

[C] 11 V/m

[D] -23 V/m



Questions No:5

Two plates are at potentials -10 V and +30 V. If the separation between the plates be 2 cm. The electric field between them is

[A] 2000 V/m

[B] 1000 V/m

[C] 500 V/m

[D] 3000 V/m



Questions No:6

Charges 2q, – q and – q lie at the vertices of an equilateral triangle. The value of E and Val the centroid of the triangle will be

[A] E ≠ 0 and V ≠ 0

[B] E=0 and V=0

[C] E ≠ 0 and V=0

[D] E=0 and V ≠ 0



Questions No:7

In a uniform electric field a charge of 3 C experiences a force of 3000 N. The potential difference between two points 1 cm apart along the electric lines of force will be

[A] 10 V

[B] 100 V

[C] 30V

[D] 300V



Questions No:8

From a point charge there is a fixed point A. At that point there is an electric field of 500 V/m and potential of 3000 V. Then the distance of A from the point charge is

[A] 6m

[B] 12 m

[C] 36m

[D] 144m



Questions No:9

If E is the electric field intensity of an electrostatic field, then the electrostatic energy density is proportional to

[A] E

[B] E2

[C] \( \frac{1}{ E^2} \)

[D] E3



Questions No:10

A particle A has charge +q and a particle B has charge +4g with each of them having the same mass m. When allowed to fall from rest through the same electric potential difference, the ratio of their speed \( \frac{V_A}{ V_B} \) will become

[A] 2:1

[B] 1:2

[C] 1 : 4

[D] 4 : 1



Questions No:11

Three particles, each having a charge of 10 µ C are placed at the corners of an equilateral triangle of side 10 cm. The electrostatic potential energy of the system is (given \( \frac{1}{4πε_0} \)=9×109N-m2/C2)

[A] zero

[B] infinite

[C] 27 J

[D] 100 J



Questions No:12

A mass m = 20 g has a charge q = 3.0 mC. It moves with a velocity of 20 m/s and enters a region of electric field of n 80 N/c in the same direction as the velocity of the mass. The velocity of the mass after 3 s in this region is

[A] 80 m/s

[B] 56 m/s

[C] 44 m/s

[D] 40 m/s



Questions No:13

Four identical charges +50 µ C each are placed, one at each corner of a square of side 2 m. How much external energy is required to bring another charge of + 50 µ C from infinity to the centre of the square?

[A] 64 J

[B] 41 J

[C] 16 J

[D] 10 J



Questions No:14

Two equal charges q are placed at a distance of 2a and a third charge -2q is placed at the mid-point. The potential energy of the system is

[A] \( \frac{q^2}{8πε_0a } \)

[B] \( \frac{q^2}{8πε_0a } \)

[C] -\( \frac{7q^2}{8πε_0a } \)

[D] -\( \frac{9q^2}{8πε_0a } \)



Questions No:15

An alpha particle is accelerated through a potential difference of 106V. Its kinetic energy will be

[A] 1 MeV

[B] 2 MeV

[C] 4 MeV

[D] 8 MeV



Questions No:16

A charge of 5 C is given a displacement of 0.5 m. The work done in the process is 10 J. The potential difference between the two points will be

[A] 2V

[B] 0.25V

[C] 1 V

[D] 25 V



Questions No:17

How much kinetic energy will be gained by an ex-particle in going from a point at 70 V to another point at 50 V

[A] 40 eV

[B] 40 keV

[C] 40 MeV

[D] 0 eV



Questions No:18

The ratio of momenta of an electron and an α-particle which are accelerated from rest by a potential difference of 100 V is

[A] 1

[B] \( \sqrt\frac{2m_e}{m_α} \)

[C] \( \sqrt\frac{m_e}{m_α} \)

[D] \( \sqrt\frac{m_e}{2m_α} \)



Questions No:19

An electron enters in higher potential region V2 from lower potential region V1, then its velocity

[A] will increase

[B] will change in direction but not in magnitude

[C] will not change in direction of field

[D] will not change in direction perpendicular to field



Questions No:20

At a distance of 1 m from a fixed charge of 1 mC, a particle of mass 2 g and charge 1 µ C is held stationary. Both the charges are placed on a smooth horizontal surface. If the particle is made free to move, then its speed at a distance of 10 m from the fixed charge will be

[A] 10 ms q-1

[B] 20 ms-1

[C] 60 ms-1

[D] 90 ms-1