P199 Chapter 9

A model electric train requires 6 V to operate. When it is connected to a 120-V household circuit, a transformer is needed. If the primary coil of the transformer has 260 turns, find how many turns should have the secondary coil.

13 turns.

Magnet A has twice the magnetic field strength of magnet B, and at a certain distance it pulls on magnet B with a force of 50 N. With how much force does magnet B then pull on magnet A?

50 N.

The primary of a transformer connected to 100 V has 90 turns. The secondary has 10 turns. Find the output voltage. This is a step-down transformer.

V = 11 V.

An ideal transformer has 50 turns in the primary and 500 turns in the secondary. An input of 12 V will produce an output of a. 120 V. b. 12 V. c. 1200 V. d. none of the above.

a. 120 V.

The voltage across the input terminals of a transformer is 110 V. The primary coil has 50 loops and the secondary coil has 100 loops. The output is a. 220 V. b. 55 V. c. 110 V. d. 25 V. e. none of the above.

a. 220 V.

What are the basic differences and similarities between a generator and an electric motor? a. a generator converts mechanical energy to electrical energy; a motor converts electrical energy into mechanical energy. b. a generator and a motor are unrelated. c. a generator and a motor are basically the same thing. d. a motor converts mechanical energy to electrical energy; a generator converts electrical energy into mechanical energy.

a. a generator converts mechanical energy to electrical energy; a motor converts electrical energy into mechanical energy.

A compass needle in a magnetic field experiences a. a torque. b. a net force. c. both of these. d. none of the above.

a. a torque.

A galvanometer calibrated to read potential difference is a. voltmeter. b. an ammeter. c. an ohm meter. d. none of the above.

a. a voltmeter.

A galvanometer calibrated to read current is a. an ammeter. b. a voltmeter. c. an ohm meter. d. none of the above.

a. an ammeter.

Like kinds of magnetic poles repel while unlike kinds of magnetic poles a. attract. b. may attract or repel. c. repel also.

a. attract.

Compared with the current in the primary coil of a transformer, the current in the secondary coil a. can be greater or less. b. is greater. c. is less. d. none of the above.

a. can be greater or less.

The magnetic field lines about a straight current-carrying wire are a. circular. b. elliptical. c. spiral. d. radial.

a. circular.

A common electromagnet consists of a a. current-carrying coil with a piece of iron inside. b. bar magnet that carries an electric current. c. current-carrying wire coil.

a. current-carrying coil with a piece of iron inside.

If you break a bar magnet in half you'll a. have two magnets. b. have four magnets. c. destroy its magnetic properties. d. none of the above.

a. have two magnets.

Since magnetic force on a moving electron is always perpendicular to its direction of motion, magnetic force is unable to change an electron's a. speed. b. direction. c. speed and direction. d. none of the above.

a. speed.

When a bar magnet is broken in half, the strength of the four new poles relative to pole strength before breaking is a. the same. b. half. c. somewhat more. d. less than half.

a. the same.

Every magnet contains at least a. two poles. b. one pole. c. four poles.

a. two poles.

A step-up transformer in an electrical circuit can step up a. voltage. b. energy. c. both of these. d. neither of these.

a. voltage.

An electronic game requires 6 V for operation. With a transformer it can be powered by a 120-V outlet. If the primary has 500 turns, the secondary has a. 50 turns. b. 25 turns. c. more than 50 turns. d. 4 turns. e. none of the above.

b. 25 turns.

A current of 4 A exist in the primary coil of a transformer. The voltage across the primary coil is 110 V. What is the power output of the secondary coil? a. 27.5 W. b. 440 W. c. 880 W. d. 110 W. e. not enough information.

b. 440 W.

A transformer has an input of 6 V and an output of 42 V. If the input is changed to 12 V, the output would be a. 48 V. b. 84 V. c. 12 V. d. more than 84 V. e. none of the above.

b. 84 V.

A friend says that changing electric and magnetic fields underlie the production of light. a. disagree with your friend. b. agree with your friend. c. find a new friend.

b. agree with your friend.

Surrounding every stationary electron is a. a magnetic field. b. an electric field. c. both of these. d. neither of these.

b. an electric field.

When an electron passes through the magnetic field of a horseshoe magnet, the electron's a. speed is increased. b. direction of motion is changed. c. both of these. d. none of the above.

b. direction of motion is changed.

Power is the rate at which a. voltage can be changed. b. energy is transferred. c. current can be induced.

b. energy is transferred.

Compared with the huge force that attracts an iron tack to a strong magnet, the force that the tack exerts on the magnet is a. relatively small. b. equally huge. c. not enough information.

b. equally huge.

A device that transforms mechanical energy into electrical energy is a a. transformer. b. generator. c. magnet. d. motor. e. none of the above.

b. generator.

Compared with a motor, a generator is a. of an entirely different design. b. its opposite. c. one and the same.

b. its opposite.

Electric and magnetic fields combine to produce a. sound. b. light. c. both of these. d. none of the above.

b. light.

The ultimate source of all magnetism is a. tiny bits of iron. b. moving electric charge. c. ferromagnetic materials. d. tiny domains of aligned atoms.

b. moving electric charge.

Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a a. south pole. b. north pole. c. either of these. d. neither of these.

b. north pole.

The rate at which a transformer transforms energy is called a. electromagnetic induction. b. power. c. transformer efficiency.

b. power.

A topic that most underlies electrical studies and all of physics is a. the conservation of momentum. b. the conservation of energy. c. Newton's laws of motion.

b. the conservation of energy.

An efficient step-down transformer decreases a. energy. b. voltage. c. power. d. current. e. all of the above.

b. voltage.

A magnetic field exists in a current-carrying coil of wire a. only if the current changes. b. with or without a contained piece of iron. c. if it contains a piece of iron.

b. with or without a contained piece of iron.

When a current-carrying wire is bent into a loop, its magnetic field inside the loop a. cancels. b. weakens. c. becomes concentrated. d. none of the above.

c. becomes concentrated.

Moving electric charges are surrounded by a. magnetic fields. b. electric fields. c. both of these answers. d. neither of these answers.

c. both of these answers.

A strong magnetic field easily penetrates a. plastic coatings. b. human flesh. c. both of these. d. none of the above.

c. both of these.

Magnetism is due to the motion of electrons as they a. spin on their axes. b. move around the nucleus. c. both of these. d. neither of these.

c. both of these.

Surrounding every moving electron is a. an electric field. b. a magnetic field. c. both of these. d. neither of these.

c. both of these.

The fact that a force is exerted on a current-carrying wire when in a magnetic field is employed in a. electric meters. b. motors. c. both of these. d. neither of these.

c. both of these.

The frequency with which a magnet plunges into and out of a wire coil equals the frequency of the induced a. voltage. b. current. c. both of these. d. none of the above.

c. both of these.

The principal difference between a step-up and step-down transformer is a. different geometries. b. step-up transformers can handle more current. c. different ratios of turns for each set of loops or coils. d. none of the above.

c. different ratios of turns for each set of loops or coils.

What any type of field generation cannot create is a. electromagnetic waves. b. light. c. energy.

c. energy.

An iron nail is attracted a. more strongly to the north pole of a magnet. b. more strongly to the south pole of a magnet. c. equally to either pole of a magnet. d. none of the above.

c. equally to either pole of a magnet.

Magnet A has twice the magnetic field strength of magnet B and pulls on magnet B with a force of 100 N. The amount of force that magnet A exerts on magnet B is a. at of about 50 N. b. more than 100 N. c. exactly 100 N. d. not enough information.

c. exactly 100 N.

The magnetic field strength inside a current-carrying coil will be greater if the coil encloses a a. wooden rod. b. glass rod. c. iron rod. d. vacuum. e. none of the above.

c. iron rod.

Magnet domains normally occur in a. copper. b. silver. c. iron. d. all of the above. e. none of the above.

c. iron.

Wood does not have magnetic properties because it contains no a. iron or other metals. b. moving electrons. c. magnetic domains. d. none of the above.

c. magnetic domains.

The minimum or no magnetic force on a moving electron occurs for motion a. at non-right angles to the magnetic field direction. b. perpendicular to the magnetic field. c. parallel to the magnetic field.

c. parallel to the magnetic field.

The induced electric and magnetic fields of Maxwell are a. non-directional. b. parallel to each other. c. perpendicular to each other.

c. perpendicular to each other.

Maximum magnetic force occurs when electrons move a. in the same direction as the magnetic field. b. opposite to the magnetic field direction. c. perpendicular to the magnetic field direction. d. at non-right angles to the magnetic field direction. e. none of the above.

c. perpendicular to the magnetic field direction.

When a bar magnet is thrust at the same speed into a coil having twice the number of loops, the induced voltage is a. four times as much. b. the same, no different. c. twice as much. d. half. e. none of the above.

c. twice as much.

Electromagnetic induction is employed in a. credit card readers. b. mobile phones. c. computers. d. all of the above. e. none of the above.

d. all of the above.

The magnetic field inside a current-carrying coil increases when a. an iron core is inserted. b. current is increased. c. the number of loops of wire in the coil increases. d. all of the above. e. none of the above.

d. all of the above.

When a bar magnet is thrust into a coil of wire, a greater voltage is induced with a. faster thrusting motion. b. a stronger bar magnet. c. a greater number of loops in the coil. d. all of the above.

d. all of the above.

The energy source for a generator may be a. a waterfall. b. wind. c. steam from a turbine. d. any of these. e. none of the above.

d. any of these.

Why is iron magnetic and wood not magnetic? a. wood contains equal numbers of north and south magnetic poles, iron does not. b. wood has much smaller magnetic domains than iron does. c. wood is an electrical conductor, iron is not. d. atoms in wood are not so strongly magnetic that they organize into domains as iron atoms do.

d. atoms in wood are not so strongly magnetic that they organize into domains as iron atoms do.

Faraday's law describes a. the force between magnetic poles. b. the attraction and repulsion of magnetic poles. c. the connection between current, voltage, and resistance. d. electromagnetic induction. e. all of the above.

d. electromagnetic induction.

Compared with the power input to an ideal transformer, the power output is a. less. b. greater. c. either greater or less. d. the same.

d. the same.

The metal detectors that travelers walk through at airports operate via a. Ohm's law. b. Coulomb's law. c. civil laws. d. Newton's laws. e. Faraday's law.

e. Faraday's law.

Voltage produced by a generator alternates because a. alternations in the mechanical energy input. b. the current it produces alternates. c. it produces pulses of current. d. effectively it is an ac motor in reverse. e. the magnetic field that produces it alternates.

e. the magnetic field that produces it alternates.