Question 1

Which of the following statements best describes the principle of charge conservation?

Accepted Answer

The algebraic sum of all electric charges in any closed system is constant.

Question 2

A plastic rod is rubbed with fur and then brought near a neutral metal ball suspended by an insulating thread. What happens to the ball and why?

Accepted Answer

The ball is attracted because the rod polarizes the charges in the ball, causing an attractive force.

Question 3

Which equation correctly expresses Coulomb's Law for the magnitude of the force between two point charges $$q_1$$ and $$q_2$$ separated by a distance $$r$$?

Accepted Answer

$$F = \dfrac{1}{4\pi\$$epsilon_0$$} \dfrac{|q_1$ q_2$|}{r^2$}$$

Question 4

A charged comb can pick up small pieces of paper. What is the physical explanation for this phenomenon?

Accepted Answer

The comb polarizes the molecules in the paper, resulting in an attractive force.

Question 5

Which of the following is true about the electric field inside a conductor in electrostatic equilibrium?

Accepted Answer

The electric field is zero everywhere inside the conductor.

Question 6

A point charge $$q is $$placed at the center of a spherical Gaussian surface of radius $$R. $$What is the total electric flux through the surface?

Accepted Answer

$$\Phi_E = \dfrac{q}{\$$epsilon_0$$}$$

Question 7

Which of the following best describes the effect of inserting a dielectric material between the plates of a charged capacitor (with the battery disconnected)?

Accepted Answer

The capacitance increases and the voltage decreases.

Question 8

A parallel-plate capacitor with plate area $$A$$ and separation $$d is $$filled with a dielectric of constant $$K. $$What is the capacitance?

Accepted Answer

$$C = K\$$epsilon_0$$ \dfrac{A}{d}$$

Question 9

A resistor of resistance $$R is $$connected to a battery of emf $$\epsilon$$ and internal resistance $$r. $$What is the current in the circuit?

Accepted Answer

$$I = \dfrac{\epsilon}{R + r}$$

Question 10

Which of the following is a correct statement of Kirchhoff’s loop rule?

Accepted Answer

The sum of the potential differences around any closed loop is zero.

Question 11

A capacitor of capacitance $$C is $$charged to a voltage $$V$$ and then disconnected from the battery. What is the energy stored in the capacitor?

Accepted Answer

$$U = \dfrac{1}{2}CV^2$

Question 12

A beam of electrons moves with velocity $$\vec{v} in a $$region with a uniform magnetic field $$\vec{B}$$ perpendicular to $$\vec{v}. $$What is the direction of the magnetic force on the electrons?

Accepted Answer

Perpendicular to both $$\vec{v}$$ and $$\vec{B}$$, given by the right-hand rule but opposite for electrons.

Question 13

Which of the following is the correct SI unit for the magnetic field $$B ($$Tesla)?

Accepted Answer

$$1\ \mathrm{T} = 1\ \mathrm{N}\cdot\mathrm{A}^{-1}\cdot\mathrm{m}^{-1}$$

Question 14

A circuit contains a $$10\ \Omega$$ resistor and a $$1.0\ \mu\mathrm{F}$$ capacitor in series with a $$12\ \mathrm{V}$$ battery. What is the time constant $$	au$$ for the charging process?

Accepted Answer

$$	au = RC = 10\ \Omega 	imes 1.0 	imes 10$$^{-6}$$\ \mathrm{F} = 1.0 	imes 10$$^{-5}$$\ \mathrm{s}$$

Question 15

Which of the following best describes the behavior of the electric field at the surface of a conductor with surface charge density $$\sigma$$?

Accepted Answer

The electric field is perpendicular to the surface and has magnitude $$\dfrac{\sigma}{\$$epsilon_0$$}.$$

Question 16

A positive charge $$q$$ moves in the $$+z$$ direction and experiences a magnetic force in the $$+y$$ direction. What can you conclude about the $$x-$$component of the magnetic field at the particle’s position?

Accepted Answer

$$B_x \u003e 0$$

Electric Charge and Electric Field: Foundations of Electrostatics

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