Deck 6: Electricity and Magnetism

Question 1

The electrons in an atom

A) are bound to it permanently.
B) are some distance away from the nucleus.
C) have more mass than the nucleus.
D) may be positively or negatively charged.

Answer 1

are some distance away from the nucleus.

Question 2

The conventional unit of battery capacity is the ampere-hour, which is actually a unit of

A) energy.
B) power.
C) potential difference.
D) electric charge.

Answer 2

electric charge.

Question 3

A negative electric charge

A) interacts only with positive charges.
B) interacts only with negative charges.
C) interacts with both positive and negative charges.
D) may interact with either positive or negative charges, depending on circumstances.

Answer 3

interacts with both positive and negative charges.

Question 4

Which of the following statements is correct?

A) Electrons carry electric currents.
B) The motion of electrons produces electric currents.
C) Moving electrons constitute electric currents.
D) Electric currents are carried by conductors and insulators only.

Question 5

When the voltage across a certain resistance is V, the power delivered is P. If the voltage is halved to V/2, the power delivered becomes

A) P/2.
B) P/4.
C)

D)

)
/4)

Question 6

Ohm's law

A) holds only for metals.
B) holds for all conducting materials.
C) is a consequence of conservation of energy.
D) is a fundamental law of nature.

Question 7

A kilowatt hour is a unit of

A) energy.
B) power.
C) potential difference.
D) electric charge.

Question 8

When a current passes through a resistance, the electric energy that is lost

A) becomes heat.
B) becomes magnetic energy.
C) is returned to the source of the current.
D) disappears.

Question 9

If undisturbed, an electric current in a superconducting wire loop

A) will decrease to a stop in a few seconds.
B) will decrease to a stop in a day or two.
C) will continue indefinitely.
D) will gradually increase.

Question 10

An object has a positive electric charge whenever

A) it has an excess of electrons.
B) it has a deficiency of electrons.
C) the nuclei of its atoms are positively charged.
D) the electrons of its atoms are positively charged.

Question 11

Relative to the electric force between two protons, the gravitational force between them is

A) weaker.
B) equal in magnitude.
C) stronger.
D) Any of these choices could be correct, depending on how far apart the protons are.

Question 12

A molecule that has lost an electron becomes a

A) positive ion.
B) negative ion.
C) nucleus.
D) superconductor.

Question 13

Coulomb's formula F = KQ₁Q₂/R² gives the force between two charges in free space. The value of K

A) is the same under all circumstances.
B) is different for positive and negative charges.
C) depends on the masses of the charged particles.
D) equals the charge on the electron.

Question 14

The watt, the unit of power, is equal to the

A) volt)ampere).
B) volt/ampere.
C) ampere/volt.
D) volt)ohm).

Question 15

Which of the following statements is not true?

A) Protons are positively charged.
B) The proton mass is greater than the electron mass.
C) The proton mass is almost the same as the neutron mass.
D) A proton in an atom circulates around its nucleus.

Question 16

Atoms and molecules are normally

A) electrically neutral.
B) negatively charged.
C) positively charged.
D) ionized.

Question 17

The volt is the unit of electric

A) current.
B) potential difference.
C) potential energy.
D) resistance.

Question 18

Which of the following statements is not true?

A) The positive charge in an atomic nucleus is due to the protons it contains.
B) All protons have the same charge.
C) Protons and electrons have charges equal in magnitude although opposite in sign.
D) Protons and electrons have equal masses.

Question 19

The nucleus of an atom

A) contains most of the atom's mass.
B) is nearly as large as the atom.
C) is electrically neutral.
D) may contain protons, neutrons, and electrons.

Question 20

Superconductivity occurs in certain substances

A) only at very low temperatures.
B) only at very high temperatures.
C) at all temperatures.
D) only when they are in the liquid state.

Question 21

The resistance of a 30-W, 12-V light bulb is

A) 0.21 ohms.
B) 0.4 ohms.
C) 2.5 ohms.
D) 4.8 ohms.

Question 22

A current-carrying wire is in a magnetic field with the direction of the current perpendicular to that of the field.

A) The wire tends to move parallel to the field.
B) The wire tends to move perpendicular to the field.
C) The wire tends to turn until it is perpendicular to the field.
D) The wire has no tendency to move or to turn.

Question 23

A magnet does not exert a force on

A) an unmagnetized iron bar.
B) a magnetized iron bar.
C) a stationary electric charge.
D) a moving electric charge.

Question 24

The power rating of an electric motor that draws a current of 3 A when operated at 240 V is

A) 80 W.
B) 720 W.
C) 1080 W.
D) 2160 W.

Question 25

When a magnetized iron bar is strongly heated, its magnetic field

A) becomes weaker.
B) becomes stronger.
C) reverses its direction.
D) is unchanged.

Question 26

When an observer moves past a stationary electric charge, she detects

A) only an electric field.
B) only a magnetic field.
C) both an electric and a magnetic field.
D) Any of these choices, depending on her speed.

Question 27

A current-carrying loop in a magnetic field always tends to turn until the plane of the loop is

A) parallel to the field.
B) perpendicular to the field.
C) either parallel or perpendicular, depending on the direction of the current.
D) at a 45-degree angle with the field.

Question 28

The primary coil of a transformer is connected to a source of alternating current of voltage V. The voltage of the secondary current is

A) lower than V.
B) equal to V.
C) higher than V.
D) Any of these choices could be correct, depending on the ratio of turns in the transformer coils.

Question 29

A current-carrying wire is in a magnetic field with the direction of the current parallel to that of the field.

A) The wire tends to move parallel to the field.
B) The wire tends to move perpendicular to the field.
C) The wire tends to turn until it is parallel to the field.
D) The wire has no tendency to move or to turn.

Question 30

An electric iron draws a current of 15 A when connected to a 120-V power source. Its resistance is

A) 0.125 ohms.
B) 8 ohms.
C) 16 ohms.
D) 1800 ohms.

Question 31

A drawing of the field lines of a magnetic field provides information on

A) the direction of the field only.
B) the strength of the field only.
C) both the direction and the strength of the field.
D) the source of the field.

Question 32

Two charges repel each other with a force of 10^-6 N when they are 10 cm apart. When they are brought closer together until they are 2 cm apart, the force between them becomes

A) 4 × 10^-8 N.
B) 5 ×10^-6 N.
C) 8 × 10^-6 N.
D) 2.5 × 10^-5 N.

Question 33

A magnet attracts

A) all substances.
B) only iron and iron alloys and repels nothing.
C) iron and iron alloys and repels other substances.
D) some substances and repels others.

Question 34

The voltage needed to produce a current of 8 A in a resistance of 12 ohms is

A) 0.67 V.
B) 1.5 V.
C) 4 V.
D) 96 V.

Question 35

Direct electric current cannot be used to operate

A) electric motors.
B) electric heaters.
C) electromagnets.
D) transformers.

Question 36

Two charges, one positive and the other negative, are initially 2 cm apart and are then pulled away from each other until they are 8 cm apart. The force between them is now smaller by a factor of

A) 2.
B) 4.
C) 16.
D) 32.

Question 37

The current with which a transformer is used

A) must be dc.
B) must be ac.
C) may be either dc or ac.
D) may be neither dc nor ac.

Question 38

A compass needle tends to

A) line up perpendicular to a magnetic field.
B) line up parallel to a magnetic field.
C) turn slowly in a constant magnetic field.
D) point only toward the North Pole.

Question 39

A current is flowing south along a power line. Neglecting the earth's field, the direction of the magnetic field under the power line is

A) north.
B) south.
C) east.
D) west.

Question 40

Two charges of +Q are 1 cm apart. If one of the charges is replaced by a charge of -Q, the magnitude of the force between them is

A) zero.
B) smaller.
C) the same.
D) larger.

Question 41

Three 12-V batteries cannot be connected to give a voltage for the set of

A) 6 V.
B) 12 V.
C) 24 V.
D) 36 V.

Question 42

The electric energy stored in a 6-V battery rated at 20 Ah is

A) 120 J.
B) 7.2 kJ.
C) 12 kJ.
D) 432 kJ.