Question 1

A set of charges are placed equidistant from a point P at a distance $$R. $$What is the total electric potential at point P due to these charges?

Accepted Answer

$$V_P = \sum \frac{kq}{R} = \frac{k}{R} \sum q $$

Question 2

If the net charge on a symmetric shell is zero, what happens to the electric field vector at the center?

Accepted Answer

It vanishes due to symmetry.

Question 3

A conducting shell has a point charge $$+2Q at $$its center. What is the net charge induced on the outer surface of the shell?

Accepted Answer

$$+2Q$$

Question 4

Why does the net charge enclosed by a conducting shell vanish when the electric field inside is zero?

Accepted Answer

Because of charge conservation and Gauss's law.

Question 5

Two conducting spheres are connected and share a total charge of $$80\ \mu C. If $$the radius of the larger sphere is three times that of the smaller, how is the charge distributed?

Accepted Answer

The larger sphere gets $$60\ \mu C$$, the smaller gets $$20\ \mu C.$$

Question 6

If the separation distance $$d$$ between two plates is doubled, what happens to the electric field $$E if $$the potential difference is held fixed?

Accepted Answer

$$E is $$halved.

Question 7

A solenoid is filled with a ferromagnetic material. How does the magnetic field inside change compared to an empty solenoid?

Accepted Answer

It increases by a large factor.

Question 8

For a current loop, what does the right-hand rule indicate about the direction of the magnetic field for an upward current?

Accepted Answer

The field points upward.

Question 9

When a piece of iron is inserted into a solenoid, what happens to the current after the insertion is complete?

Accepted Answer

The current returns to its original value.

Question 10

What is the displacement current term in Maxwell's equations responsible for?

Accepted Answer

A changing electric field.

Question 11

The direction of propagation of an electromagnetic wave is given by the Poynting vector $$\vec{S} = \vec{E} 	imes \vec{B} / \mu_0$. If $$\vec{E}$$ is along the x-direction and $$\vec{B}$$ is along the y-direction, what is the direction of propagation?

Accepted Answer

Along the z-direction.

Question 12

If the potential difference across a capacitor is $$V$$ and the separation between plates is $$d$$, what is the electric field between the plates?

Accepted Answer

$$E = \frac{V}{d}$$

Question 13

A charge $$q is $$brought from infinity to a point P with potential $$V_P. $$What is the work done?

Accepted Answer

$$W = qV_P$$

Question 14

What is the magnetic field inside an empty solenoid of length $$L$$ and $$N$$ turns carrying current $$I$$?

Accepted Answer

$$B = \mu_0$ N I / L$$

Question 15

If a conducting shell is threaded with electric flux $$\Phi$$, what must be true about the net charge enclosed?

Accepted Answer

It must vanish.

Question 16

If the electric field inside a conductor is zero, what can be said about the potential inside?

Accepted Answer

It is constant throughout.

Question 17

What is the effect of doubling the radius of a conducting sphere on its potential, assuming the charge remains constant?

Accepted Answer

The potential is halved.

Question 18

If the net electric field vector from two symmetric charge distributions is nonzero, what direction does it point?

Accepted Answer

From W to E, horizontally to the right.

Question 19

What is the physical significance of the Poynting vector $$\vec{S} in $$electromagnetic waves?

Accepted Answer

It represents the direction of energy propagation.

Question 20

What law explains why the current in a loop decreases when a ferromagnetic material is inserted, then returns to its original value?

Accepted Answer

Lenz's law.

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