physics final
What is a solenoid? What is a solenoid called when an iron rod is inserted in its center? What advantage is gained by this addition?
A long, helically wound coil of insulated wire; electromagnet; A more powerful magnet is created.
How is it possible to induce a current in a wire that moves through a magnetic field without the use of a battery or an electrical power supply?
A moving charge can be deflected by a magnetic field and as long as the motion of the charge is not parallel to the magnetic field the charge experiences a magnetic force. The effect of this force is equivalent to replacing the moving segment of wire and the magnetic field with a battery or other electrical power supply.
Use the magnetic domain model to compare and contrast hard and soft magnetic materials.
According to the magnetic domain model, both hard and soft magnetic materials have large groups of neighboring atoms whose net electron spins are aligned. Soft magnetic materials tend to gain or lose their domain alignments easily, while hard magnetic materials retain their domain alignments. Soft magnetic materials are easily magnetized, but lose their magnetism easily while hard magnetic materials are difficult to magnetize but retain their magnetism for long periods of time.
What is back emf? Does it increase or decrease motor efficiency? Explain.
Back emf is an induced emf in a motor's rotating coil. It decreases motor efficiency, since the back emf reduces the net supply current available in the motor's coil.
How does the term wave-particle duality of light relate to electromagnetic waves? What are these "particles" called? How does the behavior of a highenergy particle compare to a low-energy particle?
Electromagnetic waves exhibit both wave and particle behavior depending on the wave's frequency (or wavelength). When an electromagnetic wave behaves more like a stream of particles, the "particles" are called photons. A photon is a particle that carries energy but has zero rest mass. A highenergy photon behaves more like a particle, while a low-energy photon behaves more like a wave.
How do most commercial power plants obtain the mechanical energy that is needed to rotate the generator's turbine blades?
Falling water or steam produced by heating water turns the blades of a turbine.
Why do magnetic poles always occur in pairs?
Magnetic poles cannot be isolated no matter how many times a magnet is cut or subdivided.
Choose one type of electromagnetic wave on the electromagnetic spectrum and describe its wavelength, frequency, and energy properties. Identify two applications of the electromagnetic wave.
Microwaves have long wavelengths, low frequency, and relatively low energy. Microwaves are used to cook food, transmit telephone, computer and satellite data, and radar.
List three ways to induce a current in a circuit loop, using only a magnet.
Move the circuit loop into or out of the magnetic field. Rotate the circuit loop in the magnetic field so that the angle between the plane of the circuit loop and magnetic field changes. Vary the intensity of the magnetic field by rotating the magnet.
What is mutual inductance? What important electrical device is based on it?
Mutual inductance is the process by which a changing magnetic field in the primary circuit's coil induces a current in the secondary circuit's coil and vice versa. Transformer.
How do power companies reduce the amount of power lost to resistive heating in long-distance transmission lines? Why? What device is used to achieve this goal?
Power companies use a high emf and a low current. Since the power lost is equal to I^2R, reducing the current by a factor of 10 reduces the power lost by a factor of 100. Transformer.
Identify one type of electromagnetic wave with a long wavelength. Describe at least two of its applications, and explain why the selected wave's long wavelength is important for both applications.
Radio waves work well for transmitting information across long distances because the long wavelengths can easily travel around objects. Radio waves help scientists understand deep space objects because the long wavelengths of radio waves pass through Earth's atmosphere
Why does a current-carrying wire experience a magnetic force when the wire is placed perpendicular to the magnetic field?
The electric particles moving through the wire are also moving through the magnetic field. The resultant force on the wire is the sum of the individual magnetic forces on the charged particles.
What is the electromagnetic spectrum?
The electromagnetic spectrum is a graphic way to represent different types of electromagnetic waves and illustrate the relationship of these waves in terms of wavelength, frequency, and energy.
If the head of an iron nail touches a magnet, the nail will become a magnet by induction. If the nail touches the north pole of the magnet, what kind of pole is at the point of the nail? Explain.
The end of the magnetized nail touching the north pole of the magnet will be a south pole by induction. Otherwise, the magnet would repel it. The tip of the nail that points away from the magnet must have the opposite polarity and thus will be a north pole.
Explain how the terms energy, electromagnetic force, electromagnetic wave, and electromagnetic radiation are related to one another.
The energy of an electromagnetic wave is stored in the electromagnetic fields, which exert an electromagnetic force on charged particles. This energy transported by an electromagnetic wave is called electromagnetic radiation.
Thoroughly describe the magnetic field characteristics as an induced current is produced in a coil of wire by an approaching and receding magnet.
When an applied magnetic field approaches the coil of wire, the direction of the induced current produces an induced magnetic field that is in a direction opposite the approaching (or strengthening) magnetic field. As a result, these magnetic fields repel each other. When the applied magnetic field moves away from the coil of wire, the direction of the induced current once again produces a magnetic field that is in a direction opposite the receding (or weakening) magnetic field. This time, however, the induced magnetic field is in the same direction as the receding magnetic field. As a result, these magnetic fields attract each other.
An electron moves north at a velocity of 4.5 104 m/s and has a force of 7.2 1018 N exerted on it. If the magnetic field points upward, what is the magnitude of the magnetic field? a. 1.0 mT c. 3.6 mT b. 2.0 mT d. 4.8 mT
a. 1.0 mT
The rms current in an ac current is 3.6 A. Find the maximum current. a. 5.1 A c. 2.8 A b. 4.7 A d. 1.8 A
a. 5.1 A
Since more magnetic field lines cross the area that is near the pole of a magnet, what does this indicate about the magnetic field strength in that location? a. It is stronger. b. It is weaker. c. It is entering the magnet. d. It is leaving the magnet.
a. It is stronger.
All of the following statements about magnetic field lines around a permanent magnet are true except which one? a. Magnetic field lines appear to end at the north pole of a magnet. b. Magnetic field lines have no beginning or end. c. Magnetic field lines always form a closed loop. d. In a permanent magnet, the field lines actually continue within the magnet itself.
a. Magnetic field lines appear to end at the north pole of a magnet.
Which of the following statements about magnetic field lines is not true? a. Magnetic field lines form open or closed loops. b. Magnetic field lines appear to begin at the north pole of a magnet. c. Magnetic field lines have no beginning or end. d. Magnetic field lines appear to end at the south pole of a magnet.
a. Magnetic field lines form open or closed loops.
You have three marbles, A, B, and C, that look identical. Each of them contains either a magnet or a piece of iron. You have observed that A sticks to B, but B does not stick to C. a. Could all three contain iron? b. Could all three contain magnets? c. Which of them contain magnets? Which contain iron?
a. No b. No c. Magnet: A; Iron: B and C
Which of the following conditions will decrease the magnitude of an induced current through a circuit loop rotating in a magnetic field? a. Reduce the loop's rate of rotation. b. Increase the size of the loop. c. Increase the magnetic field strength. d. Reduce the number of loops that are parallel to the magnetic field.
a. Reduce the loop's rate of rotation.
All of the following statements about ac rms values and maximum values are true except which one? a. Rms values may equal maximum values. b. Rms values are always less than maximum values. c. Rms values are approximately 70 percent of the maximum values. d. Rms values are different from maximum values because the alternating current is at its maximum only for an instant.
a. Rms values may equal maximum values.
Which of the following statements about back emf is not true? a. Since back emf is an induced current, the net current available to the motor increases. b. The faster the coil rotates, the greater the back emf becomes. c. The ac current applied to a motor causes the induced magnetic field to reverse regularly. d. The induced magnetic field is always repelled by the fixed magnetic field.
a. Since back emf is an induced current, the net current available to the motor increases.
Which compass needle orientation in the figure on the right might correctly describe the magnet's field at that point? a. a b. b c. c d. d
a. a
Where is the magnitude of the magnetic field around a permanent magnet greatest? a. close to the poles b. far from the poles c. The magnitude is equal at all points on the field. d. The magnitude depends on the material of the magnet.
a. close to the poles
Which of the following terms correctly describes the shape of the magnetic field around a long, straight current-carrying wire? a. cylindrical b. parallel c. perpendicular d. elliptical
a. cylindrical
According to the transformer equation, ΔV2 = N2/N1 ΔV1, the relationship between the potential difference and number of turns is a. direct. b. indirect. c. inverse. d. exponential.
a. direct.
In a permanent magnet, a. domain alignment persists after the external magnetic field is removed. b. domain alignment becomes random after the external magnetic field is removed. c. domains are always randomly oriented. d. the magnetic fields of the domains cancel each other.
a. domain alignment persists after the external magnetic field is removed.
Where is energy stored in electromagnetic waves? a. in the oscillating electric and magnetic fields b. in the moving charged particles c. in the motion of the electromagnetic waves d. all of the above
a. in the oscillating electric and magnetic fields
The rms current is _____________ the maximum current. a. less than b. equal to c. greater than d. the square root of
a. less than
Which conversion process is the basic function of the electric generator? a. mechanical energy to electrical energy b. electrical energy to mechanical energy c. low voltage to high voltage, or vice versa d. alternating current to direct current
a. mechanical energy to electrical energy
A bar magnet falls through a loop of wire with constant velocity, and the north pole enters the loop first. The induced current will be greatest when the magnet is located so that the loop is a. near either the north or the south pole. b. near the north pole only. c. near the middle of the magnet. d. with no acceleration, the induced current is zero.
a. near either the north or the south pole.
How many electromagnetic forces exist? a. one c. three b. two d. four
a. one
Electromagnetic waves consist of _______________ electric and magnetic fields. a. oscillating b. constant c. parallel d. longitudinal
a. oscillating
Maximum emf occurs when the plane of a wire loop is a. parallel to the magnetic field. b. perpendicular to the magnetic field. c. decelerating in the magnetic field. d. accelerating in the magnetic field.
a. parallel to the magnetic field.
A current-carrying conductor in and perpendicular to a magnetic field experiences a force that is a. perpendicular to the current. b. parallel to the current. c. inversely proportional to the potential difference. d. inversely proportional to the velocity.
a. perpendicular to the current.
What is the path of an electron moving parallel to a uniform magnetic field? a. straight line b. circle c. ellipse d. parabola
a. straight line
According to Lenz's law, if the applied magnetic field changes, a. the induced field attempts to keep the total field strength constant. b. the induced field attempts to increase the total field strength. c. the induced field attempts to decrease the total field strength. d. the induced field attempts to oscillate about an equilibrium value.
a. the induced field attempts to keep the total field strength constant.
Lenz's law states that a. the magnetic field of the induced current is in a direction to produce a field that opposes the change causing it. b. the magnetic field of the induced current is in a direction to produce a field that cancels out the change causing it. c. the magnetic field of the induced current is in a direction to produce a field that supersedes the change causing it. d. none of the above
a. the magnetic field of the induced current is in a direction to produce a field that opposes the change causing it.
A generator with a single loop produces the greatest magnetic force on the charges and the greatest induced emf when a. the plane of the loop is parallel to the magnetic field. b. half of the loop segments are moving perpendicular to the magnetic field. c. the plane of the loop is perpendicular to the magnetic field. d. none of the above
a. the plane of the loop is parallel to the magnetic field.
Consider two long, straight, parallel wires, each carrying a current I. If the currents move in the same direction, a. the two wires will attract each other. b. the two wires will repel each other. c. the two wires will exert a torque on each other. d. neither wire will exert a force on the other.
a. the two wires will attract each other.
An electron that moves with a speed of 3.0 104 m/s perpendicular to a uniform magnetic field of 0.40 T experiences a force of what magnitude? (qe = 1.60 1019 C) a. 2.2 X 10^24 N c. 4.8 X 10^-14 N b. 1.9 X 10^-15 N d. 0 N
b. 1.9 X 10^-15 N
An ac generator has a maximum output emf of 215 V. What is the rms potential difference? a. 145 V c. 216 V b. 152 V d. 304 V
b. 152 V
A potential difference of 115 V across the primary of a step-down transformer provides a potential difference of 2.3 V across the secondary. What is the ratio of the number of turns of wire on the primary to the number of turns on the secondary? a. 1:50 c. 25:1 b. 50:1 d. 1:25
b. 50:1
A step-down transformer has 2500 turns on its primary and 5.0 X 10^1 turns on its secondary. If the potential difference across the primary is 4850 V, what is the potential difference across the secondary? a. 1.0 V c. 110 V b. 97 V d. 240 V
b. 97 V
Which statement is correct? a. The magnetic field of an induced current increases the approaching magnetic field. b. According to the principle of energy conservation, an induced field attempts to keep the total field strength constant c. An induced electric field opposes an applied magnetic field. d. Lenz's law is used to find the average induced emf.
b. According to the principle of energy conservation, an induced field attempts to keep the total field strength constant
Which of the following reasons best supports the conclusion that electricity and magnetism are two aspects of a single electromagnetic force? a. The electromagnetic force obeys the inverse-square law. b. Both electric and magnetic fields produce forces on charged particles. c. The electromagnetic force is one of the four fundamental forces in the universe. d. none of the above
b. Both electric and magnetic fields produce forces on charged particles.
How can the magnitude of the induced emf be increased? a. Decrease the length of the wire. b. Increase the velocity of the wire as it moves through the magnetic field. c. Decrease the strength of the magnetic field. d. none of the above
b. Increase the velocity of the wire as it moves through the magnetic field.
All of the following statements about the electromagnetic force are true except which one? a. It is one of the four fundamental forces in the universe. b. It exerts a force on either charged or uncharged particles. c. It obeys the inverse-square law. d. It is produced by—and produces—electric and magnetic fields.
b. It exerts a force on either charged or uncharged particles.
Which of the following statements correctly describes the behavior of magnets? a. Like poles attract each other, and unlike poles repel each other. b. Like poles repel each other, and unlike poles attract each other. c. Both like and unlike poles can attract and repel each other depending on the surrounding materials. d. none of the above
b. Like poles repel each other, and unlike poles attract each other.
Which of the following statements about Earth's magnetic field is true? a. The geographic North Pole of Earth and Earth's magnetic north pole are at the same location. b. The geographic South Pole of Earth and Earth's magnetic north pole are relatively close to each other. c. The north needle of a compass always points to the geographic North Pole of Earth. d. The north needle of a compass points to Earth's magnetic north pole.
b. The geographic South Pole of Earth and Earth's magnetic north pole are relatively close to each other.
What do radio waves, microwaves, X rays, and gamma rays all have in common? a. They are produced in the same way. b. They are electromagnetic waves. c. They are detected in the same way. d. They store the same amount of energy.
b. They are electromagnetic waves.
Which of the following situations is not true for magnets? a. Like poles repel each other. b. Unlike poles repel each other. c. North poles repel each other. d. A north pole and a south pole will attract each other.
b. Unlike poles repel each other.
All electromagnetic waves are produced by ______________ charges. a. stationary b. accelerating c. neutral d. constant
b. accelerating
What is the path of an electron moving perpendicular to a uniform magnetic field? a. straight line b. circle c. ellipse d. parabola
b. circle
Motors are machines that convert a. mechanical energy into motion. b. electrical energy into mechanical energy. c. mechanical energy into quantum energy. d. none of the above
b. electrical energy into mechanical energy.
Which conversion process is the basic function of the electric motor? a. mechanical energy to electrical energy b. electrical energy to mechanical energy c. low voltage to high voltage, or vice versa d. alternating current to direct current
b. electrical energy to mechanical energy
The right-hand rule states that the thumb of the right hand is to be placed in what direction when grasping a wire? a. in a direction opposite of the current b. in the direction of the current c. in the direction of Earth's magnetic north pole d. none of the above
b. in the direction of the current
According to the right-hand rule, in what direction will the fingers curl? a. in the direction of the current b. in the direction of the magnetic field, B c. in the direction of the magnetic field's movement d. in the direction of the magnetic field's force
b. in the direction of the magnetic field, B
Where is energy stored in electromagnetic waves? a. in the wave's moving atoms b. in the oscillating electric and magnetic fields c. in the electromagnetic force d. in the wave's directional vector
b. in the oscillating electric and magnetic fields
A generator converts a. electrical energy into mechanical energy. b. mechanical energy into electrical energy. c. mechanical energy into steam. d. steam into mechanical energy.
b. mechanical energy into electrical energy.
The greatest induced emf occurs when segments of a wire loop are a. moving parallel to the magnetic field. b. moving perpendicularly to the magnetic field. c. decelerating in the magnetic field. d. accelerating in the magnetic field.
b. moving perpendicularly to the magnetic field.
When the dc current equals Imax, the power dissipated in an ac circuit equals ____________ the power dissipated in a dc current. a. one-fourth b. one-half c. double d. quadruple
b. one-half
According to the right-hand rule, what is the direction of the force on an electron? a. out of the palm of the hand b. out of the back of the hand c. in the direction of the thumb d. in the direction of the fingers
b. out of the back of the hand
The energy transported by electromagnetic waves is called electromagnetic a. propagation. b. radiation. c. variation. d. deviation.
b. radiation.
When a bar magnet and coil approach each other, the magnetic field produced by the induced current in the coil ______________ the approaching magnetic field of the bar magnet. a. attracts b. repels c. inverts d. displaces
b. repels
How is the direction of a magnetic field, B, defined at any location? a. the direction toward which the south pole of a compass needle points b. the direction toward which the north pole of a compass needle points c. the direction that is parallel to the imaginary magnetic field lines d. the direction that is perpendicular to Earth's magnetic field
b. the direction toward which the north pole of a compass needle points
According to the right-hand rule, if a current-carrying wire is grasped in the right hand with the thumb in the direction of the current, the four fingers will curl in the direction of a. the magnetic force, Fmagnetic. b. the magnetic field, B. c. the current's velocity, v. d. the current's path, P.
b. the magnetic field, B.
Electricity may be generated by rotating a loop of wire between the poles of a magnet. The induced current is greatest when a. the plane of the loop is parallel to the magnetic field. b. the plane of the loop is perpendicular to the magnetic field. c. the magnetic flux through the loop is a minimum. d. the plane of the loop makes an angle of 45° with the magnetic field.
b. the plane of the loop is perpendicular to the magnetic field.
Consider two long, straight, parallel wires, each carrying a current I. If the currents move in opposite directions, a. the two wires will attract each other. b. the two wires will repel each other. c. the two wires will exert a torque on each other. d. neither wire will exert a force on the other.
b. the two wires will repel each other.
What is the name of the device that changes a small ac applied emf to a larger one or a large applied emf to a smaller one? a. converter b. transformer c. inverter d. exchanger
b. transformer
A generator's maximum output is 220 V. Calculate the rms potential difference. a. 110 V c. 160 V b. 150 V d. 310 V
c. 160 V
An electron moves across Earth's equator at a speed of 2.5 106 m/s and in a direction 35° north of east. At this point, Earth's magnetic field has a direction due north, is parallel to the surface, and has a value of 0.10 104 T. What is the magnitude of the force acting on the electron due to its interaction with Earth's magnetic field? (qe = 1.60 1019 C) a. 5.1 X 10^-18 N c. 3.3 X 10^-18 N b. 4.0 X 10^-18 N d. 2.3 X 10^-18 N
c. 3.3 X 10^-18 N
Which of the following statements about the orientation and effects of Earth's magnetic field is not true? a. The geographic North Pole of Earth is near the magnetic south pole. b. A compass needle that can rotate both perpendicularly and parallel to the surface of Earth, points down at the magnetic south pole. c. A compass needle always indicates the direction of true north. d. The geographic South Pole of Earth corresponds to the magnetic north pole.
c. A compass needle always indicates the direction of true north.
All of the following are ways to induce an emf in a conductor except which one? a. Deflect a charge in a magnetic field. b. Change the size of the loop in a magnetic field. c. Connect the conductor to a power supply. d. Change the strength of the magnetic field.
c. Connect the conductor to a power supply.
Which of the following statements about magnetic fields, B, is not true? a. Magnetic fields are vector quantities. b. Magnetic fields have both magnitude and direction. c. Magnetic field strength increases as the distance from the magnetic source increases. d. Magnetic fields are regions in which magnetic forces can be detected.
c. Magnetic field strength increases as the distance from the magnetic source increases.
If the secondary emf is less than the primary emf, which of the following is true about the number of turns in the coils? a. N2 is equal to N1. b. N2 is greater than N1. c. N2 is less than N1. d. N1 is less than N2.
c. N2 is less than N1.
Which of the following statements about the right-hand rule is not true? a. The fingers indicate the direction of the magnetic field. b. The thumb indicates the direction of a particle's movement in the magnetic field. c. The direction of the magnetic force is always parallel to the magnetic field. d. The direction of the magnetic force exerted on a proton is out of the palm of the hand.
c. The direction of the magnetic force is always parallel to the magnetic field.
Which of the following statements about the magnetic field lines of a solenoid is not true? a. The field lines inside a solenoid point in the same direction and are nearly parallel. b. The field lines inside a solenoid are uniformly spaced and close together. c. The field lines outside a solenoid are uniformly spaced but further apart. d. The field lines outside a solenoid do not always point in the same direction.
c. The field lines outside a solenoid are uniformly spaced but further apart.
Given the following equation, B = Fmagnetic/qv , which of the following statements is true? a. The magnetic field, B, is directly proportional to q. b. The magnetic field, B, is directly proportional to v. c. The magnetic field, B, is directly proportional to Fmagnetic. d. The magnetic field, B, is directly proportional to Fmagnetic, q, and v.
c. The magnetic field, B, is directly proportional to Fmagnetic.
Which of the following statements best describes how a generator induces a current? a. The magnetic field strength is varied. b. A wire loop is moved in and out of the magnetic field. c. The orientation of the loop is changed with respect to the magnetic field. d. The rotation of the loop is reversed periodically.
c. The orientation of the loop is changed with respect to the magnetic field.
In a primary-secondary coil combination, which of the following conditions is met in the primary coil when the current in the secondary coil is at its maximum? a. The current is maximum in a positive direction. b. The current is maximum in a negative direction. c. The rate of current change is maximum. d. The voltage is maximum in a positive direction.
c. The rate of current change is maximum.
The magnetic field of a current loop is most similar to that of a(n) a. horseshoe magnet. b. circular magnet. c. bar magnet. d. irregular magnet.
c. bar magnet.
In a two-coil system, the mutual inductance depends on a. only the geometrical properties of the coils. b. only the orientation of the coils to each other. c. both the geometrical properties of the coils and their orientation to each other. d. neither the geometrical properties of the coils nor their orientation to each other.
c. both the geometrical properties of the coils and their orientation to each other.
If a proton is released at the equator and falls toward Earth under the influence of gravity, the magnetic force on the proton will be toward the ________________ assuming the magnetic field is directed toward the north at this location. a. north c. east b. south d. west
c. east
How can the polarity or direction of an induced current be reversed? a. by reversing the direction of the conductor's motion b. by reversing the direction of the magnetic field's motion c. either a or b d. It cannot be reversed.
c. either a or b
The lines of the magnetic field around a current-carrying wire a. point away from the wire. b. point toward the wire. c. form concentric circles around the wire. d. are parallel with the wire.
c. form concentric circles around the wire.
In a magnetized substance, the domains a. are randomly oriented. b. cancel each other. c. line up mainly in one direction. d. can never be reoriented.
c. line up mainly in one direction.
A current can be induced in a closed circuit without the use of a battery or an electrical power supply by moving the circuit through a a. high temperature field. c. magnetic field. b. gravitational field. d. nuclear field.
c. magnetic field.
Electromagnetic waves are _________________ electric and magnetic fields. a. transverse c. oscillating b. constant d. parallel
c. oscillating
The direction of the force on a current-carrying wire in an external magnetic field is a. perpendicular to the current only. b. perpendicular to the magnetic field only. c. perpendicular to both the current and the magnetic field. d. parallel to the current and to the magnetic field.
c. perpendicular to both the current and the magnetic field.
What term refers to electromagnetic waves as particles? a. cathodes b. rays c. photons d. diodes
c. photons
Which of the following parts is used to convert alternating current into direct current? a. conducting or slip rings b. brushes c. split slip rings or commutators d. axis connectors
c. split slip rings or commutators
The energy produced by an alternating current with a maximum value of Imax is not the same as that produced by a direct current of the same value because a. the alternating current reverses direction. b. the alternating current is less efficient. c. the alternating current is at its maximum value only for an instant. d. the alternating current moves electrons at a slower rate.
c. the alternating current is at its maximum value only for an instant.
The induced current in a closed loop of wire is zero if a. the plane of the loop is perpendicular to the magnetic field. b. the plane of the loop is tilted into the magnetic field. c. the plane of the loop is parallel to the magnetic field. d. the plane of the loop rotates in the magnetic field.
c. the plane of the loop is parallel to the magnetic field.
When does the magnetic force on a charge moving through a constant magnetic field reach its maximum value? a. when the charge moves parallel to the magnetic field b. when the charge moves at any angle to the magnetic field c. when the charge moves perpendicular to the magnetic field d. when the charge is stationary to the magnetic field
c. when the charge moves perpendicular to the magnetic field
A 2.0 m wire segment carrying a current of 0.60 A oriented parallel to a uniform magnetic field of 0.50 T experiences a force of what magnitude? a. 0.60 N c. 0.15 N b. 0.30 N d. 0.0 N
d. 0.0 N
A step-up transformer used on a 120 V line has 95 turns on the primary and 2850 turns on the secondary. What is the potential difference across the secondary? a. 30 V c. 2400 V b. 1800 V d. 3600 V
d. 3600 V
Which of the following statements about the magnetic field, B, around a current-carrying wire is not true? a. B is proportional to the current in the wire. b. B is inversely proportional to the distance from the wire. c. The lines of B form concentric circles about the wire. d. B is independent of the current in the wire.
d. B is independent of the current in the wire.
Which of the following statements about the electromagnetic force is not true? a. The magnitude of the electromagnetic force is proportional to the charge. b. The electromagnetic force is proportional to the electric field strength. c. The electromagnetic force is proportional to the magnetic field strength. d. The electromagnetic force is inversely proportional to the charge
d. The electromagnetic force is inversely proportional to the charge
Which of the following statements about ac generators is not true? a. The output current from the generator changes its direction at regular intervals. b. The emf alternates from positive to negative. c. A graph of Δemf versus Δt is similar to a sine curve. d. The frequency of alternating current is constant.
d. The frequency of alternating current is constant.
In soft magnetic materials such as iron, what happens when an external magnetic field is removed? a. The domain alignment persists. b. The orientation of domains fluctuates. c. The material becomes a hard magnetic material. d. The material returns to an unmagnetized state.
d. The material returns to an unmagnetized state.
A stationary positive charge, Q, is located in a magnetic field, B, which is directed toward the right. The direction of the magnetic force on Q is a. toward the right. b. up. c. down. d. There is no magnetic force.
d. There is no magnetic force.
How does an electromagnetic wave propagate itself? a. A changing magnetic field induces an electric field perpendicular to the magnetic field. b. A changing electric field induces a magnetic field perpendicular to the electric field. c. Changing electric and magnetic fields produce a transverse wave that is perpendicular to both of the oscillating fields. d. all of the above
d. all of the above
In what way can a current be induced in a circuit? a. Move the circuit into or out of a magnetic field. b. Vary the intensity and/or direction of the magnetic field. c. Rotate the circuit in the magnetic field. d. all of the above
d. all of the above
One useful way to model magnetic field strength is to define a quantity called magnetic flux ΦM . Which of the following definitions for magnetic flux, ΦM , is correct? a. the number of field lines that cross a certain area b. ABcosθ c. (surface area) X (magnetic field component normal to the plane of surface) d. all of the above
d. all of the above
The strength of a solenoid can be increased by a. increasing the current. b. increasing the number of wire loops. c. inserting an iron rod through the center of the coil. d. all of the above
d. all of the above
Under which of the following conditions is the net magnetic force on a charged particle equal to zero? a. when the particle is stationary b. when the particle is moving parallel to the magnetic field c. when the particle is not charged d. all of the above
d. all of the above
What describes ΦM? a. magnetic flux b. the number of field lines that cross a certain area c. ABcosθ d. all of the above
d. all of the above
What is rms (root-mean-square) current? a. the value of alternating current that gives the same heating effect that the corresponding value of direct current does b. an important measure of the current in an ac circuit c. the amount of direct current that would dissipate the same energy in a resistor as is dissipated by the instantaneous alternating current over a complete cycle d. all of the above
d. all of the above
Which of the following equations shows the correct relationship between rms emf, rms current, and resistance? a. ΔVrms = IrmsR c. Irms = ΔVrms/R b. R = ΔVrms/Irms d. all of the above
d. all of the above
Which of the following options can be used to generate electricity? a. Move the circuit loop into and out of a magnetic field. b. Change the magnetic field strength around the circuit loop. c. Change the orientation of the circuit loop with respect to the magnetic field. d. all of the above
d. all of the above
Which of the following statements about electromagnetic radiation is true? a. It transfers energy to objects in the path of the electromagnetic waves. b. It can be converted to other energy forms. c. It transports the energy of electromagnetic waves. d. all of the above
d. all of the above
Which of the following statements correctly describes electromagnetic waves? a. The electric and magnetic fields are at right angles to each other. b. The electric and magnetic fields are at right angles to the direction that the wave is moving. c. Electromagnetic waves are transverse waves. d. all of the above
d. all of the above
Both rms current and rms emf values are _________________ less than the maximum values. a. never b. seldom c. often d. always
d. always
What path does a positively charged particle moving perpendicularly to a uniform magnetic field follow? a. erratic b. helical c. straight d. circular
d. circular
Which of the following modifications to a solenoid would be most likely to decrease the strength of its magnetic field? a. removing its iron rod core and increasing the number of coils b. increasing the current and reducing the number of coils c. reducing the number of coils and inserting an iron core d. decreasing the current and reducing the number of coils
d. decreasing the current and reducing the number of coils
What do physicists call large groups of atoms whose net spins are aligned because of strong coupling between neighboring atoms? a. magnetic zones b. magnetic regions c. magnetic sectors d. magnetic domains
d. magnetic domains
According to Lenz's law, the magnetic field of an induced current in a conductor will a. enhance the applied field. b. heat the conductor. c. increase the potential difference. d. oppose a change in the applied magnetic field.
d. oppose a change in the applied magnetic field.
A loop of wire is held in a vertical position at the equator with the face of the loop facing in the east-west direction. What change will induce the greatest current in the loop? a. raising the loop to a higher elevation b. moving the loop north c. rotating the loop so its face is vertical d. rotating the loop so its face is north-south
d. rotating the loop so its face is north-south
In what direction do compass needles deflect in relation to the concentric circles of the magnetic field that is found around a current-carrying wire? a. away from the concentric circles b. perpendicular to the concentric circles c. toward Earth's North Pole irrespective of the concentric circles d. tangential to the concentric circles
d. tangential to the concentric circles
Which statement describes Earth's magnetic declination? a. the angle between Earth's magnetic field and Earth's surface b. Earth's magnetic field strength at the equator c. the tendency for Earth's field to reverse itself d. the angle between true north and north indicated by a compass
d. the angle between true north and north indicated by a compass
A current is moving from north to south through a long wire that is lying horizontally on a table. What is the direction of the magnetic force if the magnetic field is directed up and out of the table? a. toward the north b. toward the east c. toward the south d. toward the west
d. toward the west
Under which of the following situations can a current be induced in a circuit? a. when an open circuit moves through a magnetic field b. when both a closed circuit and magnetic field are moving, but not with respect to each other c. when neither the closed circuit nor magnetic field are moving d. when a closed circuit moves through a magnetic field
d. when a closed circuit moves through a magnetic field
Two loops of wire are arranged so that a changing current in the primary will induce a current in the secondary. The secondary loop has twice as many turns as the primary loop. As long as the current in the primary is steady at 3.0 A, the current in the secondary will be a. 6.0 A. c. 1.5 A. b. 3.0 A. d. zero.
d. zero.
The rms emf across a resistor is equal to what?
the rms current multiplied by the resistance (or Irms • R )
A bar magnet is suspended and allowed to rotate freely. If the magnetic field of Earth is considered to be equivalent to that of a large bar magnet, which pole of the suspended magnet would point toward the magnetic north pole of Earth?
the south pole
What is a turbine's rotational motion used for in commercial power plants?
to turn wire loops (or a coil of wire) in a magnetic field