# Electrostatics Mock Test-5

Questions No:1

An electric dipole when placed in a uniform electric field E will have minimum potential energy if the dipole moment makes the following angle with E

[A] π

[B] π/2

[C] zero

[D] 3π /2

Questions No:2

Electric field at a far away distance r on the axis of a dipole is E0. What is the electric field at a distance 2r on perpendicular bisector?

[A] E0/16

[B] -E0/16

[C] E0/8

[D] -E0/8

Questions No:3

The SI unit of electric flux is

[A] Weber

[B] Newton/coulomb

[C] Volt x metre

[D] Joule/coulomb

Questions No:4

If the electric flux entering and Leaving an enclosed surface respectively is φ1 andφ2 the electric charge inside the surface will be

[A] (φ1+φ2)ε0

[B] (φ2-φ1)ε0

[C] (φ1+φ2)/ε0

[D] (φ2-φ1)/ε0

Questions No:6

A wire of linear charge density λ passes through a cuboid of length l, breadth b and height h in such a manner that flux through the cuboid is maximum. The position of wire is now changed, so that the flux through the cuboid is minimum. l > b > h, then the ratio of maximum flux to minimum flux will be_______

[A] $\frac{\sqrt{(l^2+b^2+h^2)}}{h}$

[B] $\frac{\sqrt{(l^2+b^2)}}{h}$

[C] $\frac{h}{\sqrt{(l^2+b^2)}}$

[D] $\frac{l}{\sqrt{(l^2+b^2+h^2)}}$ 100

Questions No:7

If the flux of the electric field through a closed surface is zero

[A] the electric field must be zero everywhere on the surface

[B] the electric field may be zero everywhere on the surface

[C] the charge inside the surface must be zero

[D] the charge in the vicinity of the surface must be zero

Questions No:8

Charge of 2 C is placed at the centre of a cube. What is the electric flux passing through one face?

[A] 1/(3ε0)

[B] (1/4) ε0

[C] 2/ε0

[D] 3/ε0

Questions No:9

If the flux of the electric field through a closed surface is zero

[A] the electric field must be zero everywhere on the surface

[B] the electric field must be non-zero everywhere on the surface

[C] the net charge inside the surface must be zero

[D] the net charge in the vicinity of the surface must be zero

Questions No:10

The electric charges are distributed in a small volume. The flux of the electric field through a spherical surface of radius 10 cm surrounding the total charge is 20 V-m. The flux over a concentric sphere of radius 20 cm will be

[A] 20Vm

[B] 10 Vm

[C] 40 Vm

[D] 5 Vm

Questions No:11

For a given surface, the Gauss’s law is stated as ∫ E.ds =
From this, we can conclude that

[A] E is necessarily zero on the surface

[B] E is perpendicular to the surface at every point

[C] The total flux through the surface is zero

[D] The flux is only going out of the surface

Questions No:12

A cube of side a is placed in a uniform electric field E = E0i + E0j + E0k. Total electric flux passing through the cube would be

[A] E0a2

[B] 2E0a2

[C] 6E0a2

[D] None of the above

Questions No:13

A surface E = 10j is kept in an electric field E = 2i + 4j + 7k. How much electric flux will come out through this surface?

[A] 40 unit

[B] 50 unit

[C] 30 unit

[D] 20 unit

Questions No:14

Separation between the plates of a parallel plate capacitor is d and the area of each plate is A. When a slab of material of dielectric constant K and thickness t(c
[A] $\frac {ε_{0}A}{d+t(1-\frac{1}{K})}$

[B] $\frac {ε_{0}A}{d+t(1+\frac{1}{K})}$

[C] $\frac {ε_{0}A}{d-t(1-\frac{1}{K})}$

[D] $\frac {ε_{0}A}{d-t(1+\frac{1}{K})}$

Questions No:15

The distance between the circular plates of a parallel plate condenser 40 mm in diameter, in order to have same capacity as a sphere of radius 1 m is

[A] 0.01 mm

[B] 0.1 mm

[C] 1.0mm

[D] 10 mm

Questions No:16

A spherical condenser has inner and outer spheres of radii a and b respectively. The space between the two is filled with air. The difference between the capacities of two condensers formed when outer sphere is earthed and when inner sphere is earthed will be

[A] zero

[B] 4πε0a

[C] 4πε0b

[D] 4πε0$( \frac{ab}{b-a})$

Questions No:18

If a slab of insulating material 4×10-3 m thick is introduced between the plates of a parallel plate capacitor, the separation between plates has to be increased by 5 x 10 -3 m to restore the capacity to original value. The dielectric constant of the material will be

[A] 6

[B] 8

[C] 10

[D] 12

Questions No:21

Three capacitors of capacitances 3 µ F, 9µ F and 18 µ F are connected once in series and another time in parallel The ratio of equivalent capacitance in the two cases (Cs/Cpwill be

[A] 1:15

[B] 15:1

[C] 1 : 1

[D] 1 : 3

Questions No:22

There are 7 identical capacitors. The equivalent capacitance when they are connected in series is C. The equivalent capacitance when they are connected in parallel is

[A] $\frac{C}{49}$

[B] $\frac{C}{7}$

[C] 7C

[D] 49 C

Questions No:23

The capacitance of a parallel plate capacitor is 16µ F. When a glass slab is placed between the plates, the potential difference reduces to $\frac{1}{8}$th of the original value. What is dielectric constant of glass?

[A] 4

[B] 8

[C] 16

[D] 32