Question 1

Which of the following statements best describes the law of conservation of electric charge?

Accepted Answer

The total electric charge in an isolated system remains constant during any process.

Question 2

A neutral metal sphere is brought into contact with a positively charged rod. What happens to the sphere?

Accepted Answer

It becomes positively charged due to the transfer of electrons.

Question 3

Which of the following materials is most likely to be a good electrical conductor?

Accepted Answer

Copper

Question 4

A charged rod is brought near, but does not touch, a neutral metal sphere. The sphere is then grounded while the rod is still nearby. What is the final charge on the sphere after the ground connection and the rod are both removed?

Accepted Answer

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

Question 5

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

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

Question 6

Two charges, $$Q_1 = +2$$\ \mu C$$ and Q_2$ = -2\ \mu C$$, are placed 0.5 m apart. What is the direction of the force on $$Q_1$$ due to $$Q_2$$?

Accepted Answer

Toward $$Q_2 ($$attractive)

Question 7

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

Accepted Answer

$$E = k \frac{Q}{r^2$}$$

Question 8

A small test charge $$q is $$placed in an electric field $$E. $$What is the force $$F$$ experienced by the test charge?

Accepted Answer

$$F = qE$$

Question 9

A thin ring of radius $$a$$ carries a total charge $$Q$$ distributed uniformly. What is the electric field at a point on the axis of the ring, a distance $$x$$ from its center?

Accepted Answer

$$E = \frac{1}{4\pi\$$epsilon_0$$} \frac{Qx}{(x^2$ + a^2$)^{3/2}$$}$

Question 10

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

Accepted Answer

It is zero.

Question 11

A charged particle of mass $$m$$ and charge $$q is $$released from rest in a uniform electric field $$E. $$What is its acceleration?

Accepted Answer

$$a = \frac{qE}{m}$$

Question 12

A parallel-plate capacitor consists of two large plates separated by a small distance $$d. If $$the plates carry equal and opposite charge densities $$+\sigma$$ and $$-\sigma$$, what is the electric field between the plates (neglecting edge effects)?

Accepted Answer

$$E = \frac{\sigma}{\$$epsilon_0$$}$$

Question 13

Which of the following is NOT a correct property of electric field lines?

Accepted Answer

Field lines can cross each other.

Question 14

A water molecule is an example of a polar molecule. What does this mean?

Accepted Answer

It is neutral overall, but the charge is not evenly distributed.

Question 15

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

Accepted Answer

$$E = \frac{1}{2\pi\$$epsilon_0$$} \frac{\lambda}{x}$$

Question 16

An electric dipole is placed in a uniform electric field. Which of the following statements is true?

Accepted Answer

The dipole experiences a torque but no net force.

Question 17

The electric field at a point on the perpendicular bisector of a dipole (at distance $$r$$ where $$r \gg \ell) is $$given by:

Accepted Answer

$$E = \frac{1}{4\pi\$$epsilon_0$$} \frac{p}{r^3$}$$

Question 18

Which of the following best explains why the electric field just outside a conductor is perpendicular to the surface?

Accepted Answer

Because any parallel component would cause charges to move, violating electrostatic equilibrium.

Electric Charge and Electric Field – Study Notes (Physics for Scientists and Engineers, Ch. 21)

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