Q: Two point charges, $$q_1 = +2$$ \ \mu\mathrm{C}$$ and q_2$ = -2 \ \mu\mathrm{C}$$, are placed 10 cm apart in air. What is the magnitude of the force between them?

$$F = 3.6 \times 10$$^{3}$$ \ \mathrm{N}$$

Question 1

A glass rod is rubbed with silk, resulting in the rod becoming positively charged. Which of the following best explains this phenomenon?

Accepted Answer

Electrons are transferred from the rod to the silk, leaving the rod positively charged.

Question 2

Two point charges, $$q_1 = +2$$ \ \mu\mathrm{C}$$ and q_2$ = -2 \ \mu\mathrm{C}$$, are placed 10 cm apart in air. What is the magnitude of the force between them?

Accepted Answer

$$F = 3.6 	imes 10$$^{3}$$ \ \mathrm{N}$$

Question 3

Three point charges are placed at the vertices of an equilateral triangle of side $$a. $$Each charge has magnitude $$q. $$What is the magnitude of the net force on any one charge?

Accepted Answer

$$F = \frac{\sqrt{3}q^2$}{4\pi\$$varepsilon_0$$ a^2$}$$

Question 4

A point charge $$Q is $$placed at the center of a conducting spherical shell of inner radius $$a$$ and outer radius $$b. $$The shell is initially uncharged. What is the charge induced on the inner surface of the shell?

Accepted Answer

$$-Q$$

Question 5

Which of the following correctly describes the electric field inside a conductor in electrostatic equilibrium?

Accepted Answer

The electric field is zero everywhere inside the conductor.

Question 6

A long, straight wire carries a uniform linear charge density $$\lambda. $$What is the magnitude of the electric field at a distance $$r$$ from the wire?

Accepted Answer

$$E = \frac{\lambda}{2\pi\$$varepsilon_0$$ r}$$

Question 7

A parallel-plate capacitor with plate area $$A$$ and separation $$d is $$connected to a battery of voltage $$V. If a $$dielectric with dielectric constant $$K is $$inserted fully between the plates while the battery remains connected, what happens to the charge on the plates?

Accepted Answer

The charge increases by a factor of $$K.$$

Question 8

A point charge $$q is $$located at the origin. What is the electric potential at a distance $$r$$ from the charge, assuming the potential is zero at infinity?

Accepted Answer

$$V = \frac{q}{4\pi\$$varepsilon_0$$ r}$$

Question 9

A capacitor of capacitance $$C is $$charged to a voltage $$V$$ and then disconnected from the battery. If the plates are pulled apart so that the distance between them doubles, what is the new voltage across the plates?

Accepted Answer

$$2V$$

Question 10

Which of the following statements about the conservation of charge is correct?

Accepted Answer

Charge can neither be created nor destroyed.

Question 11

A uniformly charged ring of radius $$R$$ carries total charge $$Q. $$What is the electric field at the center of the ring?

Accepted Answer

$$E = 0$$

Question 12

A parallel-plate capacitor is filled halfway with a dielectric of constant $$K ($$the other half is vacuum). If the original capacitance was $$C_0$$, what is the new capacitance?

Accepted Answer

$$C = \frac{K+1}{2}C_0$

Question 13

A metal sphere of radius $$R$$ carries a charge $$Q. $$What is the electric field just outside the surface of the sphere?

Accepted Answer

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

Question 14

A non-conducting sphere of radius $$R$$ has a uniform charge density $$\rho. $$What is the electric field at a distance $$r \u003c R$$ from the center?

Accepted Answer

$$E = \frac{\rho r}{3\$$varepsilon_0$$}$$

Question 15

A parallel-plate capacitor is connected to a battery and reaches equilibrium. If the area of the plates is doubled while the separation remains the same, what happens to the capacitance?

Accepted Answer

The capacitance doubles.

Question 16

Which of the following best describes the relationship between electric field $$\vec{E}$$ and electric potential $$V$$?

Accepted Answer

$$\vec{E} = -
abla V$$

Question 17

A capacitor network consists of two capacitors, $$C_1$$ and $$C_2$$, connected in series. What is the equivalent capacitance $$C_{eq}$$?

Accepted Answer

$$C_{eq} = \frac{C_1$ C_2$}{C_1$ + C_2$}$$

Question 18

A charged particle moves from point $$A to $$point $$B in an $$electric field. The electric potential at $$A is$$ $$V_A$$ and at $$B is$$ $$V_B. $$What is the change in potential energy of the particle of charge $$q$$?

Accepted Answer

$$\Delta U = q(V_B - V_A)$$

Question 19

A large, flat, non-conducting plane has a uniform surface charge density $$\sigma. $$What is the magnitude of the electric field just above the surface?

Accepted Answer

$$E = \frac{\sigma}{2\$$varepsilon_0$$}$$

Question 20

A parallel-plate capacitor is charged and then disconnected from the battery. A dielectric slab is then inserted between the plates. What happens to the energy stored in the capacitor?

Accepted Answer

The energy decreases by a factor of $$K.$$

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