Chapter 22

Electrostatics

The net charge of an atom equals

a. the number of protons in its nucleus.

b. the number of electrons surrounding its nucleus.

c. zero if the atom is electrically neutral.

d. always zero.

The net charge of an atom equals

a. the number of protons in its nucleus.

b. the number of electrons surrounding its nucleus.

c. zero if the atom is electrically neutral.

d. always zero.

If a neutral atom has 22 protons in its nucleus, the number of surrounding electrons is

a. less than 22.

b. 22.

c. more than 22.

d. sometimes any of these in a neutral atom.

If a neutral atom has 22 protons in its nucleus, the number of surrounding

electrons is

a. less than 22.

b. 22.

c. more than 22.

d. sometimes any of these in a neutral atom.

Comment: Any atom with 22 protons in its nucleus with more or less than 22 electrons is not neutral.

When we say charge is conserved, we mean that charge can

a. be saved, like money in a bank.

b. not be created or destroyed.

c. be created or destroyed, but only in nuclear reactions.

d. take equivalent forms.

When we say charge is conserved, we mean that charge can

a. be saved, like money in a bank.

b. not be created or destroyed.

c. be created or destroyed, but only in nuclear reactions.

d. take equivalent forms.

Explanation: Electric charge cannot be created or destroyed. It can only be transferred from one place to another.

A negative ion has more

a. electrons than neutrons.

b. electrons than protons.

c. protons than electrons.

d. neutrons than protons plus electrons.

A negative ion has more

a. electrons than neutrons.

b. electrons than protons.

c. protons than electrons.

d. neutrons than protons plus electrons.

According to Coulomb’s law, the force between a pair of charged particles

that are brought closer together

a. decreases.

b. increases.

c. increases only if the charges are of the same sign.

d. increases only if the charges are of opposite signs.

According to Coulomb’s law, the force between a pair of charged particles

that are brought closer together

a. decreases.

b. increases.

c. increases only if the charges are of the same sign.

d. increases only if the charges are of opposite signs.

When a pair of charged particles are brought twice as close to each other, the

force between them becomes

a. twice as strong.

b. 4 times as strong.

c. half as strong.

d. one-quarter as strong.

When a pair of charged particles are brought twice as close to each other,

the force between them becomes

a. twice as strong.

b. 4 times as strong.

c. half as strong.

d. one-quarter as strong.

Comment: In accord with the inverse-square law.

Unlike Newton’s law of gravity, Coulomb’s law involves

a. force at a distance.

b. a proportionality constant.

c. an inverse-square law.

d. repulsive as well as attractive forces.

Unlike Newton’s law of gravity, Coulomb’s law involves

a. force at a distance.

b. a proportionality constant.

c. an inverse-square law.

d. repulsive as well as attractive forces.

When you scuff electrons off a rug with your shoes, your shoes become

a. negatively charged.

b. positively charged.

c. ionic.

d. electrically neutral.

When you scuff electrons off a rug with your shoes, your shoes become

a. negatively charged.

b. positively charged.

c. ionic.

d. electrically neutral.

When a cloud that is negatively charged on its bottom and positively charged on its top moves over the ground below,

the ground acquires

a. a negative charge.

b. a positive charge.

c. no charge since the cloud is electrically neutral.

d. an electrically grounded state.

When a cloud that is negatively charged on its bottom and positively charged on its top moves over the ground below,

the ground acquires

a. a negative charge.

b. a positive charge.

c. no charge since the cloud is electrically neutral.

d. an electrically grounded state.

When a negatively charged balloon is placed against a wooden door, positive charges in the wall are

a. attracted to the balloon.

b. repelled from the balloon.

c. too bound to negative charges in the door to have any effect.

d. neutralized.

When a negatively charged balloon is placed against a wooden door, positive charges in the wall are

a. attracted to the balloon.

b. repelled from the balloon.

c. too bound to negative charges in the door to have any effect.

d. neutralized.

If it takes 10 newtons of force to hold a 0.1-coulomb particle at rest in an electric

field, the strength of the field there is

a. 1 N/C.

b. 10 N/C.

c. 100 N/C.

d. 1000 N/C.

If it takes 10 newtons of force to hold a 0.1-coulomb particle at rest in an electric

field, the strength of the field there is

a. 1 N/C.

b. 10 N/C.

c. 100 N/C.

d. 1000 N/C.

In the electric field surrounding a group of charged particles, field strength is

greater where field lines are

a. thickest.

b. longest.

c. farthest apart.

d. closest.

In the electric field surrounding a group of charged particles, field strength is

greater where field lines are

a. thickest.

b. longest.

c. farthest apart.

d. closest.

Electrons on the surface of a conductor will arrange themselves such that the

electric field

a. inside cancels to zero.

b. follows the inverse-square law.

c. tends toward a state of minimum energy.

d. is shielded from external charges.

Electrons on the surface of a conductor will arrange themselves

such that the electric field

a. inside cancels to zero.

b. follows the inverse-square law.

c. tends toward a state of minimum energy.

d. is shielded from external charges.

The change in potential energy of a charged object depends on

a. the work done on it.

b. its location.

c. its mass.

d. both mass and location.

The change in potential energy of a charged object depends on

a. the work done on it.

b. its location.

c. its mass.

d. both mass and location.

Normally, a rubber balloon charged to thousands of volts has a relatively

a. large amount of charge.

b. small amount of energy.

c. small electric potential.

d. small electric field.

Normally, a rubber balloon charged to thousands of volts has a relatively

a. large amount of charge.

b. small amount of energy.

c. small electric potential.

d. small electric field.

A superconductor has the property of

a. changing from a conductor to an insulator.

b. becoming conducting when illuminated with light.

c. having a low electrical resistance.

d. All of the above.

A superconductor has the property of

a. changing from a conductor to an insulator.

b. becoming conducting when illuminated with light.

c. having a low electrical resistance.

d. All of the above.

Comment: Don’t confuse a superconductor with a semiconductor!

Electric potential and electric potential energy are

a. one and the same in most cases.

b. two terms for the same concept.

c. Both of these.

d. None of these.

Electric potential and electric potential energy are

a. one and the same in most cases.

b. two terms for the same concept.

c. Both of these.

d. None of these.

Explanation: Electric potential is electric potential energy per charge, a ratio of energy per charge in units joules per coulomb (volts). Electric potential energy has units of joules.

Voltage is electric potential energy per charge measured in units of

a. volts.

b. joules.

c. coulombs.

d. amperes.

Voltage is electric potential energy per charge measured in units of

a. volts.

b. joules.

c. coulombs.

d. amperes.

The thing that we measure in joules per coulomb is

a. electric force.

b. electric field.

c. electric current.

d. voltage.

The thing that we measure in joules per coulomb is

a. electric force.

b. electric field.

c. electric current.

d. voltage.

A capacitor can store

a. charge.

b. energy.

c. Both.

d. Neither.

A capacitor can store

a. charge.

b. energy.

c. Both.

d. Neither.