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This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.

1.

If in Coulomb’s law, there would be dependence on \(\frac{1}{r^{3}}\) in place of \(\frac{1}{r^{2}}\), then would Gauss’s law be true?

Answer»

No, Gauss’s law will be applicable for those fields for which they follow inverse square law.

2.

Where is the energy stored due to an electric charge?

Answer»

Energy is stored in the volume of electric field.

3.

Why is charge always on the outer surface of the conductor?

Answer»

As electric field inside charged sphere is zero (E = 0), therefore emergent flux from Gaussian surface will be zero.
or ϕ = 0 but, ϕ= \(\frac{q}{\varepsilon_0}\) ⇒ q = ϕε0 = 0
It means, charge inside surface will be zero. Thus, the whole charge Q will be distributed on its surface.

4.

Why does the size of a soap bubble increases on charging it?

Answer»

There is equilibrium inside positive and negative charges of soap bubble. When it is given negative charge, then the position of equilibrium start to change. To achieve this equilibrium, charges try to repel each other. Thus the surface area of bubble increases. Due to increase in surface area, the bubble increases in size.

5.

Explain volume charge density. Write its unit.

Answer»

Volume charge density: When the charge density is throughout the volume of a body, then the charge per unit volume is called volume charge density and it is represented by ρ.
∴ ρ = \(\frac{q}{V}\)
Hence the unit of ρ is Cm-3
Example: If a charge q is uniformly distributed in the whole volume of a sphere of radius R, then \(\rho =\frac { q }{ \frac { 4 }{ 3 } \pi { R }^{ 3 } } =\frac { 3q }{ 4\pi { R }^{ 3 } } \)

6.

Explain surface charge density. Write it’s unit.

Answer»

Surface charge density: When the charge is distributed on a plane or curved surface, then charge per unit area is called surface charge density of charge and represented by σ.
∴ σ = \(\frac{q}{A}\)
Where q is charge on surface of area A
∴ Unit of σ = Cm-2
Example: If q charge is distributed uniformly on sphere of radius R, then surface charge density of the sphere \(\sigma=\frac{q}{4 \pi R^{2}}\).

7.

If charge q is situated at the centre of a sphere. Now, if the charge is placed inside the cylindrical surface of same volume. Then what would be the ratio of flux leaving out the surface in both the conditions?

Answer»

In both conditions, the ratio of electric flux will be equal.

8.

Explain linear charge density. Write it’s unit.

Answer»

Linear charge density: When the charge density is along a line, then the quantity of charge per unit length is called linear charge density and it is represented by λ.
λ = \(\frac{q}{l}\), where q is charge uniformly distributed on length l.
Unit of λ = Cm-1
Example: If q charge is uniformly distributed on a ring of radius R, then the linear charge density of ring will be \(\frac{q}{2 \pi R}\)

9.

What would be the change in electric field for a charged sheet of (a) surface charge density to move from one side to another?

Answer»

Change in electric field
= E1 – E2
\(=\frac{\sigma}{2 \varepsilon_{0}}-\left(-\frac{\sigma}{2 \varepsilon_{0}}\right)=\frac{\sigma}{\varepsilon_{0}}\)

10.

At what conditions, is the electric field intensity due to a uniformly charged non-conducting sphere zero?

Answer»

Uniform charged insulating sphere has electric field intensity zero at centre and infinity.

11.

When is the electric flux leaving out the elemental area placed in electric field \(\vec{E}\) zero?

Answer»

If the area of elemental surface \(\overrightarrow{d s}\) is at 90° to electric field, then emergent out flux will be zero.

12.

Two dipoles of charges ±q are placed normally inside a cube. Then the total electric flux leaving out the cube will be:

Answer»

(c) Zero

Due to dipole, there is no area from which flux is passing. Thus the leaving out flux = 0.

13.

A square is placed in a uniform electric field E parallel to the horizontal such that the plane of the square makes an angle 30° with the field. If the side of the square is a, then the flux through the square wire be:(a) \(\frac{\sqrt{3} E a^{2}}{2}\)(b) \(\frac{E a^{2}}{2}\)(c) zero(d) none of these

Answer»

(c) zero
Since electric field is acting along, plane of the square, so the angle between area vector \(\vec A\) and \(\vec E\) is 90°. These give ϕ = EAcosθ = EAcos90 = 0.

14.

You are going in a car. It is about to lightning, then how will you protect yourself?

Answer»

We will close the window of the car. So that entire charge will lie on the surface of car.