Question 1

Which of the following statements best explains why rubbing wool against a plastic rod causes the rod to become negatively charged?

Accepted Answer

Electrons move from the wool to the plastic rod because plastic has a high electron affinity.

Question 2

A honeybee acquires a charge of $$q = +20\$$times10^{-12}$$\ 	ext{C}$$ while flying. How many electrons did it lose to acquire this charge? (Elementary charge $$e = 1.6\$$times10^{-19}$$\ 	ext{C})$$

Accepted Answer

$$1.25\$$times10^{8}$$

Question 3

Which of the following is true about conductors and insulators?

Accepted Answer

Conductors allow the free movement of electrons, while insulators prevent the motion of electrons.

Question 4

When a charged rod is brought near a neutral metal sphere without touching it, what happens to the charges in the sphere?

Accepted Answer

Electrons in the sphere move toward the rod, causing charge polarization.

Question 5

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

Accepted Answer

$$F = k\frac{|q_1q_2|}{r^2$}$$

Question 6

Two charges, $$q_1 = +10$$\ 	ext{nC}$$ and q_2$ = +10\ 	ext{nC}$$, are placed 2.0 cm apart. What is the direction of the force each exerts on the other?

Accepted Answer

The force is repulsive and points away from each other.

Question 7

A neutral pollen grain becomes charge polarized when a positively charged bee approaches. What is the physical mechanism responsible for this polarization?

Accepted Answer

The bee’s positive charge attracts the pollen’s electrons, distorting their electron cloud.

Question 8

If $$q_1 = +10$$\ 	ext{nC}$$ and q_2$ = -10\ 	ext{nC}$$ are placed 2.0 cm apart, and $$q_3 = +1.0$$\ 	ext{nC}$$ is midway between them, what is the direction of the net force on q_3$?

Accepted Answer

The net force points toward $$q_2 ($$the negative charge).

Question 9

Which of the following best describes the difference between gravitational and electric forces?

Accepted Answer

Electric forces can be both attractive and repulsive, while gravitational forces are always attractive.

Question 10

A plastic rod is rubbed with wool. After rubbing, the rod is negatively charged and the wool is positively charged. Which statement is correct?

Accepted Answer

Electrons moved from the wool to the plastic rod.

Question 11

Which unit is used to measure electric charge?

Accepted Answer

Coulomb (C)

Question 12

A charged object is brought near a neutral insulator. What happens to the atoms in the insulator?

Accepted Answer

The electron clouds are distorted, creating induced electric dipoles.

Question 13

Given $$q_1 = -50$$\ 	ext{nC}$$, q_2$ = +50\ 	ext{nC}$$, and $$q_3 = +30$$\ 	ext{nC}$$ placed as shown in a right triangle, what is the net force on q_3$ due to q_1$ and q_2$?

Accepted Answer

$$\vec{F}_3$$ points in the -x direction with magnitude $$3.8\$$times10^{-6}$$\ 	ext{N}$$

Question 14

Which trigonometric function would you use to find the side opposite a given angle in a right triangle if you know the hypotenuse?

Accepted Answer

$$\sin(	heta) = \frac{	ext{opposite}}{	ext{hypotenuse}}$$

Question 15

If two charges $$q_1$$ and $$q_2$$ are separated by distance $$r$$, and the force between them is $$F$$, what happens to the force if the distance is doubled?

Accepted Answer

The force is reduced to one-fourth.

Question 16

Which of the following is a real-world example of charge polarization?

Accepted Answer

A neutral pollen grain sticking to a positively charged bee.

Question 17

What is the value of the electrostatic constant $$k$$ used in Coulomb’s Law?

Accepted Answer

$$8.99\$$times10^9$$\ 	ext{Nm}^2/	ext{C}^2$$

Question 18

Which of the following best describes the process of charging an object by friction?

Accepted Answer

Electrons are transferred from one object to another, resulting in one object becoming positively charged and the other negatively charged.

Electric Forces and Electric Fields: Study Notes

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