Q: What is the value of the vacuum permittivity $$\$$varepsilon_0$$?

$$\$$varepsilon_0$$ = 8.85 \times 10$$^{-12}$$ \ \mathrm{C^2$/N\,m^2$}$$

Question 1

Which of the following statements best describes the difference between conductors and insulators in terms of electric charge?

Accepted Answer

In conductors, the outer electrons are weakly bound and can move freely, while in insulators, the electrons are tightly bound and cannot move freely.

Question 2

A glass rod is rubbed with silk, transferring electrons from the glass to the silk. What is the net charge on the glass rod after rubbing?

Accepted Answer

The glass rod becomes positively charged.

Question 3

According to Coulomb's Law, what is the force between two point charges $$Q_1$$ and $$Q_2$$ separated by a distance $$r in $$vacuum?

Accepted Answer

$$F = k \frac{Q_1$ Q_2$}{r^2$}$$

Question 4

What is the value of the vacuum permittivity $$\$$varepsilon_0$$?

Accepted Answer

$$\$$varepsilon_0$$ = 8.85 	imes 10$$^{-12}$$ \ \mathrm{C^2$/N\,m^2$}$$

Question 5

A positive test charge is placed in an electric field created by a negative point charge. In which direction does the force on the test charge act?

Accepted Answer

Toward the negative charge

Question 6

Which of the following best describes the superposition principle for electric fields?

Accepted Answer

The electric field at a point due to several charges is the vector sum of the fields due to each charge.

Question 7

A metal sphere is placed in a uniform electric field. What happens to the electric field inside the sphere?

Accepted Answer

It is zero.

Question 8

What is the direction of the electric field lines at the surface of a conductor in electrostatic equilibrium?

Accepted Answer

Perpendicular to the surface

Question 9

A dipole is placed in a uniform electric field. What is the net force and net torque on the dipole?

Accepted Answer

Net force is zero, net torque is nonzero unless the dipole is aligned with the field.

Question 10

What is the expression for the electric field at a distance $$r$$ from a point charge $$Q$$?

Accepted Answer

$$E = \frac{1}{4\pi\$$varepsilon_0$$} \frac{Q}{r^2$}$$

Question 11

A charged rod is brought near a neutral metal sphere without touching it. The sphere is then grounded. What is the resulting charge on the sphere after removing the ground and the rod?

Accepted Answer

The sphere acquires a charge opposite to that of the rod.

Question 12

Which of the following best describes the electric field inside a Faraday cage?

Accepted Answer

It is zero.

Question 13

What is the electric dipole moment $$\vec{p}$$ for two charges $$+Q$$ and $$-Q$$ separated by a distance $$l$$?

Accepted Answer

$$\vec{p} = Ql$$

Question 14

A water molecule is an example of a dipole. Which property of the molecule is responsible for this?

Accepted Answer

The molecule has a bent shape and unequal sharing of electrons.

Question 15

What is the work done by an electric field in rotating a dipole from $$\$$theta_1$$ = \frac{\pi}{2} to$$ $$\$$theta_2$$?

Accepted Answer

$$W = pE \cos \$$theta_2$$

Question 16

For a ring of total charge $$Q$$ and radius $$a$$, what is the electric field at a point $$x on $$the axis passing through the center of the ring?

Accepted Answer

$$E_x = \frac{1}{4\pi\$$varepsilon_0$$} \frac{Qx}{(x^2$ + a^2$)^{3/2}$$}$

Question 17

A parallel-plate capacitor consists of two large plates separated by a distance $$d$$ and carrying surface charge densities $$+\sigma$$ and $$-\sigma. $$What is the magnitude of the electric field between the plates?

Accepted Answer

$$E = \frac{\sigma}{\$$varepsilon_0$$}$$

Question 18

Which of the following is true about electric field lines?

Accepted Answer

They indicate the direction of the electric force on a positive test charge.

Question 19

A point charge $$Q is $$placed at the center of a conducting spherical shell. What is the electric field inside the conductor (but outside the cavity)?

Accepted Answer

It is zero.

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