Deck 8: Light and Electromagnetism

Question 1

How does a permanent magnet work, i.e., what is the explanation of its magnetic effects?

A) Subatomic particles known as "magnetic poles" are placed on each end of the magnet, with one type of pole placed on one end and the other type on the other end.
B) Magnets are a communist plot.
C) Electrons orbiting individual atoms in the magnet are all aligned together so that their orbital motion produces a large overall effect.
D) The material of the magnet is highly ionized, with one type of ion residing on one end of the magnet and the other type of ion residing on the other end.
E) Electric charge is permanently separated within the magnet, with positive static charge at one end and negative static charge at the other end of the magnet.

Answer 1

Electrons orbiting individual atoms in the magnet are all aligned together so that their orbital motion produces a large overall effect.

Question 2

The force between two bar magnets cannot be due to gravity, because

A) the force between magnets is far too large to be caused by gravity.
B) the force between magnets can be repulsive, while gravity must be attractive.
C) Both of the above.
D) the force of gravity is always downward, unlike the magnetic force.
E) All of the above.

Answer 2

Both of the above.

Question 3

A charged particle is placed at rest in the middle of a vacuum chamber, an enclosure that has been emptied of all matter. Consider some point X near a particular corner of the chamber. Neglecting all influences other than the charged particle, what can be said regarding electric fields and magnetic fields at point X?

A) There is both an electric field and a magnetic field at X.
B) There is no electric field at X but there is a magnetic field at X.
C) There is an electric field at X, but no magnetic field.
D) There is neither an electric field nor a magnetic field at X.
E) It is impossible to answer this question without knowing what kind of charge the particle has.

Answer 3

There is an electric field at X, but no magnetic field.

Question 4

A changing magnetic field creates an electric field. This is one way of stating

A) the magnetic force law.
B) the principle of conservation of electromagnetic fields.
C) the law of force pairs.
D) Faraday's law.
E) the electric force law.

Question 5

What form of energy do electrons have when they're at rest on the negative terminal of an isolated (not connected to an electrical circuit) batters?

A) radiant
B) electrical
C) thermal
D) chemical
E) Actually, they don't have any energy.

Question 6

Suppose you charge two transparencies by rubbing and then hold them near each other without letting them touch, and shake both of them back and forth. Regarding the electric and magnetic forces they exert on each other,

A) they will exert both and electric and magnetic forces.
B) they will exert electric forces but not magnetic forces.
C) they will exert electromagnetic forces only after five o'clock on Friday afternoons.
D) they will exert magnetic forces but not electric forces.
E) they will exert neither electric nor magnetic forces because they are not in contact with each other.

Question 7

The planetary model of the atom is a more detailed, or sophisticated, model than the simpler Greek model of the atom. The planetary model is useful because, unlike the Greek model, it can explain

A) gas pressure, including air pressure.
B) electrical phenomena such as electric current.
C) the differences between the three states of matter.
D) certain subtle "quantum" effects.
E) the microscopic meaning of thermal energy.

Question 8

Object A has an electric charge that is 10 times larger than the charge on object B. When placed near each other, how does the force by A on B compare with the force by B on A?

A) The force by A on B is 100 times smaller.
B) The force by A on B is 100 times larger.
C) They are equal.
D) The force by A on B is 10 times smaller.
E) The force by A on B is 10 times larger.

Question 9

In a single electric cord, such as a cord that connects a wall socket with an electric light,

A) there are two wires, both carrying giant pumpkins into the light bulb.
B) there is just one wire, carrying electrons into the light bulb.
C) there are two wires, one carrying electrons into the light bulb and the other carrying electrons out.
D) there are two wires, one carrying protons into the light bulb and the other carrying protons out of the light bulb.
E) there is just one wire, carrying protons into the light bulb.

Question 10

Suppose you electrically charge a transparency by rubbing it, and then hang the transparency, at rest, by a string in the center of a room. Except for the transparency and string, the room is totally evacuated of all matter. Neglecting any influences from outside the room, what kinds of fields would then be found at places inside the room but away from the transparency-- for instance, at a point near a corner of the room?

A) a magnetic field only
B) an electric field only
C) Both an electric and magnetic field
D) No fields at all, because the transparency would create electromagnetic fields only within the transparency itself
E) No fields at all, because there is nothing [no material object] at such a point

Question 11

The atomic nucleus contains

A) yogurt.
B) neutrons and electrons.
C) protons only.
D) protons and neutrons.
E) protons and electrons.

Question 12

Suppose you released a single proton from rest at some point X in an electric field, and that you then released a single electron from rest at the same point X. How would the motions of the proton and electron compare, just after their release from rest?

A) They would move in opposite directions, and the electron would move fastest.
B) They would move in opposite directions, and the proton would move fastest.
C) They would move in the same directions, and the electron would move fastest.
D) They would move in opposite directions, and at the same speeds.
E) They would move in the same directions, and the proton would move fastest.

Question 13

What is the explanation of Earth's magnetism?

A) Earth's magnetism a consequence of the world's physics professors all spinning in the same direction.
B) It is caused by a separation of charge within the Earth, with positive static charge residing at one of Earth's poles and negative static charge residing at the other pole.
C) Subatomic particles known as "magnetic poles" reside in the Earth, with one type of magnetic pole residing at Earth's north pole and the other type of magnetic pole residing at Earth's south pole.
D) It is caused by electrically charged material circulating within Earth's hot liquid core.
E) It is caused by charged, or ionized, particles circulating in the air above the solid Earth.

Question 14

An "ion" is

A) an atom having a particular number of protons in the nucleus.
B) two or more atoms stuck together.
C) an atom with an excess or deficiency of electrons.
D) a device used to press clothes.
E) an atom in an excited state.

Question 15

If you rub two transparency sheets with tissue and then hold the two transparency sheets at rest a short distance apart, they will then exert

A) no electric or magnetic forces on each other.
B) a repulsive magnetic force on each other, but no electric force.
C) an attractive electric force on each other, but no magnetic force.
D) an attractive magnetic force on each other, but no electric force.
E) a repulsive electric force on each other, but no magnetic force.

Question 16

What should be the resistance of a light bulb in order for it to draw a 2 amp current when plugged into a 120- volt outlet?

A) 1/60 ohm
B) 1/30 ohm
C) 30 ohms
D) 60 ohms
E) 480 ohms

Question 17

A neutral atom loses one of its electrons. It is then

A) either a negative or positive ion, depending on which electron was lost.
B) ashamed of itself.
C) a neutral ion.
D) a positive ion.
E) a negative ion.

Question 18

What physics principle can be demonstrated by rubbing two transparency sheets with tissue paper and then holding them near each other?

A) the electric motor
B) certain features of the frictional force
C) the electric force
D) a new feature about the gravitational force
E) the magnetic force

Question 19

An electromagnetic field

A) is a region of space where a charge would feel a force.
B) can exist in vacuum.
C) Both of the above.
D) None of the above.

Question 20

A blow dryer with a resistance of 6 ohms is plugged into a 60- volt battery. How much current does it draw?

A) 0.1 amp
B) 360 amps
C) 10 amps
D) 30 amps
E) 6 amps

Question 21

When a battery is used to light up a lightbulb,

A) electric charge builds up within the bulb, causing the bulb to light up.
B) electric charge builds up on the battery terminals but none of it actually flows through the bulb.
C) all the electrical current produced by the battery is consumed by the bulb.
D) the amount of electrical current flowing into one side of the battery is equal to the amount flowing out of the other side.
E) some of the electrical current produced by the battery is consumed by the bulb, and the rest flows back into the battery.

Question 22

A "short circuit" is best described as

A) a low resistance placed across a high voltage.
B) an electrical circuit with a very high resistance.
C) a high voltage that is not connected to an electrical circuit.
D) a high resistance placed across a low voltage.
E) an electrical circuit with a very high voltage.

Question 23

If two electrons are near each other and are moving past each other, the electromagnetic forces they exert on each other will be

A) magnetic but not electric.
B) electric but not magnetic.
C) zero.
D) both electric and magnetic.

Question 24

The filament of a lightbulb glows, while the connecting wires do not. This is because

A) the current is smaller in the lightbulb than in the wires.
B) the resistance is smaller in the lightbulb than in the wires.
C) the resistance is larger in the lightbulb than in the wires.
D) the current is larger in the lightbulb than in the wires.
E) the wires are made of a type of material that cannot heat up.

Question 25

Concerning the force holding an atom together [that is, holding the electrons into the nucleus] and the force holding the solar system together: Are these basically the same type of force?

A) Yes, both are electromagnetic forces.
B) Yes, both are gravitational forces.
C) No, nuclear forces hold an atom together while electromagnetic forces hold the solar system together.
D) No, electromagnetic forces hold atoms together while gravitational forces hold the solar system together.
E) No, nuclear forces hold an atom together while gravitational forces hold the solar system together.

Question 26

If two transparency sheets are rubbed with tissue and the transparency sheets are then held at rest a short distance from each other, the force between them will be

A) a repulsive magnetic force.
B) zero.
C) an attractive magnetic force.
D) an attractive electric force.
E) a repulsive electric force.

Question 27

An atom's "atomic number" is

A) the number of protons in its nucleus.
B) the number of electrons orbiting the nucleus of the neutral atom.
C) Both of the above.
D) the number of electrons orbiting the nucleus of the ionized atom.
E) All of the above.

Question 28

Regarding the charges of the electron, proton and neutron:

A) the proton has a positive charge, the electron has a negative charge whose strength is equal to the strength of the proton's charge, and the neutron has no charge.
B) the electron has a negative charge, the proton has a positive charge, and the neutron has a charge that can be positive or negative or zero depending on the ionization of the atom in which it resides.
C) the proton has a positive charge, the electron has a much smaller negative charge, and the neutron has no charge.
D) the proton has a positive charge, the neutron has a negative charge whose strength is equal to that of the proton's charge, and the electron has no charge.
E) these objects are charged only when they reside in an ionized atom; otherwise, all three are uncharged.

Question 29

A battery's "voltage" is

A) the amount of energy it gives to each coulomb of electrical charge.
B) the amount of kinetic energy it gives to each electron.
C) the amount of electrical resistance it can overcome.
D) the amount of electrical charge it can send around an electrical circuit in every second.
E) the amount of electrical current it produces.

Question 30

If two electrons are at rest a short distance apart, the electromagnetic forces they exert on each other will be

A) magnetic but not electric.
B) electric but not magnetic.
C) zero.
D) both electric and magnetic.

Question 31

An atom's "atomic number" is

A) the number of protons in its nucleus.
B) the number of electrons orbiting the nucleus of the neutral atom.
C) Both of the above.
D) the number of electrons orbiting the nucleus of the ionized atom.
E) All of the above.

Question 32

If a proton and an electron are placed a short distance apart,

A) they will feel no force.
B) the electron will be repelled while the proton will be attracted.
C) they will be attracted to each other.
D) they will be repelled from each other.
E) None of the above.

Question 33

Two transparency sheets are rubbed with tissue paper and then the two transparency sheets are held up near each other. This experiment demonstrates that

A) similarly- charged objects repel each other.
B) similarly- charged objects attract each other.
C) similarly- charged objects exert magnetic forces on each other.
D) differently- charged objects repel each other.
E) differently- charged objects attract each other.

Question 34

A proton is maintained at rest in the middle of a box that has no matter inside it other than the single proton. Assuming that the box is isolated from all external influences, which of the following would we expect to find at some other point X inside the box?

A) a magnetic field
B) an electric field
C) Both of the above.
D) an electric force
E) All of the above.

Question 35

Suppose that the electric force between two objects is 2 N and that you then halve the distance between the objects. The new force is

A) 0.5 N.
B) 8 N.
C) 0.25 N.
D) 1 N.
E) 4 N.

Question 36

At the microscopic level, electric currents in wires are due to

A) atoms jiggling back and forth within the wire.
B) protons [and possibly other ions] traveling along the wire.
C) the great pumpkin.
D) electromagnetic radiation.
E) electrons traveling along the wire.

Question 37

Regarding the masses of the electron, proton, and neutron:

A) the proton and neutron have roughly the same mass, and both are far more massive than the electron.
B) the proton and electron have roughly the same mass, and both are far more massive than the neutron.
C) the proton and neutron have roughly the same mass, and both are about twice as massive as the electron.
D) the proton is much more massive, while the electron and neutron have roughly the same mass.
E) the proton is the most massive, the electron is far less massive, and the neutron has a mass about midway between the proton and electron mass.

Question 38

An atom gains one extra electron. How does the resulting ion behave when it is near a positively charged transparency? How does the ion behave when it is near a negatively charged tissue?

A) The ion is repelled from both the transparency and from the tissue.
B) The ion is attracted to the positively charged transparency, but repelled from the negatively charged tissue.
C) The ion is repelled from the positively charged transparency, but attracted to the negatively charged tissue.
D) The ion is attracted to both the transparency and to the tissue.

Question 39

The magnetic forces exerted by a permanent magnet are due to

A) electrons moving in atoms.
B) a miracle.
C) equal and opposite charges placed on each of the two "poles."
D) large- scale [macroscopic] electric currents on the surface of the magnet.
E) equal and opposite magnets placed on each of the two poles.

Question 40

If two objects each carrying a charge of 1 coulomb were placed 1 meter apart, how much force would they exert on each other?

A) 9 N
B) zero
C) 1 N
D) 9 x 10⁹ N
E) 10⁶ N

Question 41

The types of current carried by the headlights of an automobile, and by a plug- in toaster in your kitchen, are

A) both DC.
B) both AC.
C) AC and DC, respectively.
D) DC and AC, respectively.
E) None of the above.

Question 42

Two small electrically charged objects are placed 12 centimeters (cm) apart, where they exert a force of 2 N on each other. How far apart must they be placed in order to exert at force of 8 N on each other?

A) 24 cm
B) 48 cm
C) 9 cm
D) 6 cm
E) 3 cm

Question 43

J. J. Thomson's experiments with a type of invisible beam known as a cathode ray demonstrated that

A) neutrons exist.
B) light is a wave.
C) electrons exist.
D) light is made of particles.
E) the atom contains a tiny nucleus containing most of the atom's mass.

Question 44

All magnetic forces are produced by

A) electromagnetic generators.
B) protons.
C) charges in motion.
D) permanent magnets.
E) stationary charges.

Question 45

Which of these is the best explanation of the "electric hair" that can occur when some people brush their hair?

A) Excess electrons flow onto both the brush and the hair, causing the hairs to repel each other and causing the brush to repel the hairs.
B) Electrons are brushed either from the hair onto the brush, or vice- versa, causing the brush and hair to be charged, so that the hairs then attract each other while the brush repels the hairs.
C) The atoms of the brush and hair are heated, causing their electrons to move faster, which spreads out the atoms and thus causes the hairs to stand up.
D) Electrons are brushed either from the hair onto the brush, or vice- versa, causing the brush and hair to be charged, so that the hairs then repel each other while the brush attracts the hairs.
E) The atoms of the brush and hair are set into rapid vibration, causing them to emit electromagnetic waves, which causes the hairs to stand up.

Question 46

Suppose you charge two transparencies by rubbing and then hold them near each other but not touching. Regarding the electric and magnetic forces they exert on each other,

A) they will exert magnetic forces but not electric forces.
B) they will exert electric forces but not magnetic forces.
C) they will exert both electric and magnetic forces.
D) they will exert neither electric nor magnetic forces because neither object is moving.
E) they will exert neither electric nor magnetic forces because they are not in contact with each other.

Question 47

The force that is exerted by a magnet as it picks up iron nails could be best described as

A) the force of attraction between the nuclei of atoms in the magnet and the nuclei of atoms in the nails.
B) the electric force exerted by electrons in the magnet, on electrons in the nails.
C) the magnetic force exerted by ions moving within the magnet on electrons moving within the nails.
D) the magnetic force exerted by electrons moving within the magnet, on electrons moving within the nails.
E) the electric force exerted by ions in the magnet on electrons in the nails.

Question 48

If a transparency sheet is rubbed with tissue and the transparency and the tissue are then held at rest a short distance from each other, the force between them will be

A) zero.
B) an attractive magnetic force.
C) a repulsive electric force.
D) an attractive electric force.
E) a repulsive magnetic force.

Question 49

A charged particle is placed at rest in the middle of a vacuum chamber, an enclosure that has been emptied of all matter. Consider some point X near a particular corner of the chamber. Neglecting all influences other than the charged particle, what can be said regarding electric fields and electric forces at point X?

A) There is no electric field at X but there is an electric force at X.
B) There is both an electric field and an electric force at X.
C) The is an electric field at X, but no electric force.
D) There is neither an electric field nor an electric force at X.
E) It is impossible to answer this question without knowing what kind of charge the particle has.

Question 50

The "atomic number" of an element that appears in the periodic table of the elements represents

A) the number of protons in the nucleus of an atom of that element.
B) the number of electrons in the nucleus of an atom of that element.
C) the number of atoms in a molecule of the element.
D) the number of neutrons in the nucleus of an atom of that element.
E) the number of nuclei in an atom of the element.

Question 51

If you rub two transparency sheets with tissue and then hold the two transparency sheets at rest a short distance apart, the electromagnetic forces they exert on each other will be

A) zero.
B) magnetic but not electric.
C) both electric and magnetic.
D) electric but not magnetic.

Question 52

One difference between moving charges and stationary charges is that

A) moving charges exert only magnetic forces, while stationary charges exert both electric and magnetic forces.
B) moving charges exert both electric and magnetic forces, while stationary charges exert only electric forces.
C) moving charges exert only magnetic forces, while stationary charges exert only electric forces.
D) moving charges stay slender, while stationary charges are couch potatoes.
E) moving charges exert both electric and magnetic forces, while stationary charges exert neither electric nor magnetic forces.

Question 53

In an electrical circuit, the number of "amperes" measures the

A) voltage around the circuit.
B) amount of energy given to each coulomb of electrical charge.
C) amount of electric current flowing around the circuit.
D) amount of electric current consumed by the circuit elements.
E) amount of thermal energy produced in the circuit.

Question 54

Two small electrically charged objects are placed 6 centimeters (cm) apart, where they exert a force of 8 N on each other. How far apart must they be placed in order to exert a force of 2 N on each other?

A) 18 cm
B) 9 cm
C) 24 cm
D) 12 cm
E) 3 cm

Question 55

Suppose you electrically charge a transparency by rubbing it, and then hang the transparency, at rest, by a string in the center of a room. Except for the transparency and string, the room is totally evacuated of all matter. Neglecting any influences from outside the room, what kinds of forces would then be found at places inside the room but away from the transparency-- for instance, at a point near a corner of the room?

A) an electric force only
B) a magnetic force only
C) Both an electric and magnetic force
D) No forces at all, because there is no electric or magnetic field at such a point
E) No forces at all, because there is no material object at such a point

Question 56

Is the force holding the electrons into their atomic orbits in an individual atom basically the same as the force that hold the sun's planets in their orbits? Why or why not?

A) Yes; it is the force of gravity in both cases.
B) Yes; it is the centrifugal force in both cases.
C) No; gravity holds the sun's planets in their orbits, while nuclear forces hold the electrons in their orbits.
D) No; the sun's energy source is nuclear fusion, and fusion does not occur within individual atoms.
E) No; gravity holds planets in their orbits, while the electromagnetic force holds electrons in their orbits.

Question 57

Ernest Rutherford's experiments in which alpha rays pass through a thin piece of metal foil demonstrated that

A) neutrons exist.
B) light is made of particles.
C) the atom contains a tiny nucleus containing most of the atom's mass.
D) electrons exist.
E) light is a wave.

Question 58

Of the four known fundamental forces, the one that holds electrons into their orbits in atoms is

A) gravitational.
B) centrifugal.
C) electromagnetic.
D) the strong nuclear force.
E) Nonsense-- these electrons have no forces acting on them.

Question 59

Since matter is made of electrically charged particles, why don't we feel electric forces all the time?

A) Because electric forces cannot be exerted across the nearly empty space.
B) Because the effect of the electric force is absorbed by the air that normally surrounds us.
C) Because the atoms in each small portion of ordinary matter are at rest, so they produce no electromagnetic force.
D) Because there is no electric current in ordinary matter, so there can be no net macroscopic effect.
E) Because matter contains as many electrons as protons, leading to no net macroscopic effect.

Question 60

If you rub a transparency sheet with tissue and then hold the transparency sheet and the tissue at rest a short distance apart, they will then exert

A) a repulsive magnetic force on each other, but no electric force.
B) a repulsive electric force on each other, but no magnetic force.
C) an attractive electric force on each other, but no magnetic force.
D) an attractive magnetic force on each other, but no electric force.
E) no electric or magnetic forces on each other.

Question 61

If two electrons are at rest a short distance apart, they will feel

A) both electric and magnetic forces.
B) a repulsive electric force, but no magnetic force.
C) an attractive electric force, but no magnetic force.
D) no electromagnetic forces.
E) a magnetic force but no electric force.

Question 62

A proton moves through a small box that is isolated from all external influences and that has no matter inside it other than the single proton. Which of the following would we expect to find at some other point X [away from the proton] inside the box?

A) a magnetic field
B) an electric field
C) Both of the above.
D) an electric force
E) no fields or forces of any kind

Question 63

If the distance between two charged objects and the charge on each of them are all doubled, the electric force by either one on the other is

A) reduced to one- quarter of the original force.
B) halved.
C) unchanged.
D) doubled.
E) quadrupled.

Question 64

An atom's "atomic number" is

A) the number of protons in its nucleus.
B) the number of electrons orbiting the nucleus of the ionized atom.
C) Both of the above.
D) None of the above.

Question 65

In an isolated battery (not connected to an electrical circuit),

A) there is no excess of electrons or protons on either terminal.
B) there are excess electrons on the positive terminal but no excess of protons on the negative terminal.
C) there are excess protons on the negative terminal and excess electrons on the positive terminal.
D) there are excess electrons on the negative terminal but no excess protons on the positive terminal.
E) there are excess electrons on the negative terminal and excess protons on the positive terminal.

Question 66

When a transparency sheet is rubbed with a tissue and the transparency and tissue are then held at rest a short distance apart,

A) a spark will jump between them, because the rubbing causes electrons to jump from one object to the other.
B) the transparency and the tissue exert magnetic forces on each other, because the electron orbits in the two objects are all put into the same alignment.
C) the two objects exert electric forces on each other, because the electron orbits in the two objects are all put into the same alignment.
D) the two objects exert magnetic forces on each other, because electrons are rubbed off of one and onto the other.
E) the two objects exert electric forces on each other, because electrons are rubbed off of one and onto the other.

Question 67

An atom loses its two outermost electrons. How does the resulting ion behave when it is near a positively charged transparency? How does the ion behave when it is near a negatively charged tissue?

A) The ion is repelled from both the transparency and from the tissue.
B) The ion is repelled from the positively charged transparency, but attracted to the negatively charged tissue.
C) The ion is attracted to the positively charged transparency, but repelled from the negatively charged tissue.
D) The ion is attracted to both the transparency and to the tissue.

Question 68

Earth's magnetism arises from

A) the Wizard of Oz.
B) electric currents in the upper atmosphere.
C) charged particles at rest on Earth's surface and on clouds in the lower atmosphere.
D) electric currents in Earth's interior.
E) electric currents in the sun.

Question 69

Faraday's law tells us that

A) charges create electric fields.
B) a changing electric field creates a magnetic field.
C) moving charges create magnetic fields.
D) a changing magnetic field creates an electric field.
E) magnetic fields create electric fields.

Question 70

Suppose that the electric force between two objects is 2 N and that you then double the distance between the objects. The new force is

A) 1 N.
B) 8 N.
C) 0.5 N.
D) 0.25 N.
E) 4 N.