PHYS 1100 Chpt 14,15,16,17
Suppose that water waves have a wavelength of 2.6 m and a period of 1.7 s. What is the velocity of these waves? The velocity of the waves is____m/s.
(1 / 1.7 s) x 2.6 m = 1.53 m/s
The magnetic flux through a coil of wire changes from 23 T·m^2 to zero in a time of 0.50 s. What is the magnitude of the average voltage induced in the coil during this change? The magnitude of the average voltage induced in the coil is _____V.
(23−0) T⋅m^2 / 0.50 s ε=46 V
A longitudinal wave on a Slinky has a frequency of 7.2 Hz and a speed of 1.5 m/s. What is the wavelength of this wave? The wavelength of the wave is____m.
1.5 / 7.2 = 0.208
A string with a length of 1.75 m is fixed at both ends. If the string is plucked so that there are five nodes along the string in addition to those at either end, what is the wavelength of the interfering waves for this mode? The wavelength of the interfering waves is____m.
1.75 m / 3 = 0.5833 m
Two current-carrying wires are parallel to one another and separated by 1 cm. If the distance between them is increased to 2 cm the new force will be what factor times the original force?
1/2
Captain Ahab notices that the waves passing the anchored Pequod are 10 feet from crest to crest, and that each minute 4 crests pass. The wave speed is
10 ft x 4 crests = 40 ft/min
Suppose that water waves coming into a dock have a velocity of 2.1 m/s and a wavelength of 4 m. With what frequency do these waves meet the dock? The water waves meet the dock with a frequency of____Hz.
2.1 / 4 = 0.525
A wire carries a current of 9 A. How much charge flows past a point on the wire in a time of 4 s? The amount of charge that flows past a point on the wire in 4 s is_____C.
9 A x 4 s = 36 C
A transformer has 18 turns of wire in its primary coil and 90 turns in its secondary coil. Is this a step-down transformer? If an alternating voltage with an effective voltage of 120 V is applied to the primary, what is the effective voltage induced in the secondary coil. The effective voltage induced in the secondary coil is _____V.
No ΔV2=120 V×(90 / 18) ΔV2=600 V
A little magnetic compass has a needle whose tips are clearly labeled N and S. The compass is placed next to a single circular loop of wire lying flat on a wooden table. The current in the loop is clockwise. What happens?
None of these choices are correct
Which type of motor typically runs at a fixed speed?
an alternating current motor
The magnetic field lines produced by a current in a straight wire
are directed in concentric circles around the wire.
Suppose that the magnetic field passing through a coil of wire varies with time, as shown in the graph. Which of the following plots correctly shows the correct induced voltage?
figure b
The north pole of a hand-held bar magnet is brought near the north pole of a second bar magnet lying on the tablet. How will the second magnet tend to move?
it will be repelled and move away
What is the force exerted by one current-carrying wire on another due to?
magnetic effects
A permanent magnet is produced when
magnetic fields of large groups of individual atoms are permanently aligned.
If an electron is placed at rest near a bar magnet, the electron will
not move at all.
What would happen to the voltage the battery delivers to the resistor if a transformer is used, as shown in the diagram?
nothing
Magnetic fields affect
only electric charges in motion
According to Lenz's Law the direction of the induced current produced by a changing magnetic flux is such as to produce a magnetic field that
opposes the change in the original magnetic flux.
A long straight wire carries a current. A positive charge moves toward the wire in a direction perpendicular to the wire. The direction of the force on the charge will be
parallel to the wire opposite the direction of the current.
If we regard the Earth as a magnet, does what does its magnetic South Pole coincide with geographically?
the North Pole
In what respect is a simple ammeter designed to measure the electric current like an electric motor?
the ammeter has a permanent magnet to provide a magnetic field that interacts with a current provided by an external source of Emf
The principle of superposition tells us that, if two waves cross paths,
the amplitude is the sum of the individual amplitudes.
Two particles move into a magnetic field. They enter moving at the same speed and direction. The magnitude of the charge on each is known to be the same. One particle curls to the right and the other to the left upon entering the field, the leftward moving particle moves in a larger circle than the rightward moving particle. From this we can say that
the leftward moving particle has more mass and its charge is opposite the other particle.
A magnetic compass points towards the north geographic pole of the Earth because
there is a south magnetic pole near the north geographic pole.
A positive charge is released from rest near a bar magnet. The magnetic force on the charge
there is no magnetic force on the charge.
A uniform magnetic field is directed horizontally towards the east, and a negative charge is moving east through this magnetic field. In what direction, if at all, is the magnetic force on the particle?
there is no magnetic force on the particle
The primary difference between infrared and visible light is that
they have different wavelengths.
Electromagnetic waves are generally
transverse waves
When playing tennis, if you hit the ball off of the top end of the racket, an uncomfortable standing wave vibration is produced in the racket. This wave is
transverse.
Electrons flow around a circular wire loop in a horizontal plane, in a direction that is clockwise when viewed from above. This causes a magnetic field. Inside the loop, the direction of this field is
up, toward the viewer.
Light with a wavelength of 470 nm is incident upon a double slit with a separation of 0.3 mm (0.3×10-3 m). A screen is located 1.5 m from the double slit. At what distance from the center of the screen will the fourth dark fringe appear? The fourth dark fringe will appear at a distance of____mm.
(3+ 1/2 )(470 nm)×1.5 m / (0.3 mm) y=8.225 mm (3 is the forth dark fringe)
Light with a wavelength of 520 nm is incident upon a double slit with a separation of 0.3 mm (3×10-4 m). A screen is located 1.5 m from the double slit. At what distance from the center of the screen will the first bright fringe beyond the center fringe appear? The first bright fringe will appear_____cm beyond the center fringe.
(520×10^-9 m) (1.5 m) / 0.3×10^-3 m y=0.26 cm
Two long bar magnets are aligned so that north poles face each other. The magnets are separated by 1 cm, and a repulsive force between the north poles is 0.04 N. When the separation is increased to 2 cm the force will be
0.010 N.
The speed of electromagnetic waves in air is 3.0 × 108 m/s. What is the wavelength of FM radio waves having a frequency of 3.0 × 108 Hz?
1.0 m
A transformer has 200 turns on the primary and 20 turns on the secondary. The primary is connected to a direct current source of 100 millivolts. The voltage in the secondary coil will be
10 millivolts.
A string with a length of 1.35 m is fixed at both ends. What is the longest possible wavelength for the traveling waves that can interfere to form a standing wave on this string? The longest possible wavelength is__m. If waves travel with a speed of 130 m/s on this string, what is the frequency associated with this longest wavelength?
2 × 1.35 m = 2.7 m 130 m/s / 2.7 m = 48.1481 Hz
Two long parallel wires, each carrying a current of 12 A, lie at a distance of 20 cm from each other. What is the magnetic force per unit length exerted by one wire on the other? The magnetic force per unit length exerted by one wire on the other is_____×10-4 N/m.
2×(1×10^−7 N/A^2)×12 A×12 A / 0.02m = 1.44×10^−4 N/m
Sound waves have a speed of 340 m/s in room-temperature air. What is the wavelength of the sound waves for the musical tone, which has a frequency of 1400 Hz? The wavelength of the sound waves is____m.
340 / 1400 = 0.243
A step-up transformer is designed to produce 1840 V from a 104-V ac source. If there are 384 turns on the secondary coil, how many turns should be wound on the primary coil?
384×(104 V / 1840 V) N1=22 turns
Bar A has one end painted green and the other end red and may or may not be a magnet. A student brings the north pole of a bar magnet M close to the green end of A. He observes that the green end is attracted. He can conclude that
A might be a magnet; this observation does not provide enough information to determine whether or not it is.
Which of these will always produce a magnetic field?
A moving charge
The correct expression for magnetic flux through area A, where B is a constant magnetic field and A is an area perpendicular to the field, is
B × A.
The magnetic force on a 60-cm straight segment of wire carrying a current of 7 A is 8 N. What is the magnitude of the component of magnetic field perpendicular to the wire? The magnitude of the component of magnetic field perpendicular to the wire is___T
B=8 N / (7 A)×(0.6 m) B=1.9048 T
The magnetic force on a particle with positive charge, q, moving at speed, v, at right angles to a region of magnetic field strength, B, is given by
F = vB/q.
A straight segment of wire has a length of 9 cm and carries a current of 19 A. It is oriented at right angles to a magnetic field of 0.5 T. Calculate the magnitude of the magnetic force on the segment of wire. The magnitude of the magnetic force on the segment of wire is___N
F=(19 A)(0.09 m)(0.5 T ) F=0.855 N
A particle with a charge of 0.9 C is moving at right angles to a uniform magnetic field with a strength of 0.5 T. The velocity of the charge is 850 m/s. What is the magnitude of the magnetic force exerted on the particle? The magnitude of the magnetic force exerted on the particle is___N
F=0.5 T×0.9 C×850 m/s F=382.5 N
A transformer has 18 turns of wire in its primary coil and 90 turns in its secondary coil. An alternating voltage with an effective value of 110 V is applied to the primary coil. At the secondary coil, an alternating voltage with an effective value of 550 V is obtained. A current of 22 A is supplied to the primary coil of the transformer. Calculate the maximum effective current in the secondary coil. The maximum effective current in the secondary coil is____A.
I2 = 22 A×(110 V / 550 V) I2=4.4 A
When a current is induced by a changing magnetic field B1, the current always produces a second magnetic field B2 such that
It is not possible to tell whether the combined field is stronger or weaker than B1 without knowing how B1 is changing
End A of a Slinky is held motionless near the ceiling. End B is held on the floor so that there is a slight stretch. End B is quickly rotated one half turn about the axis of the Slinky and then returned to its original position, so as to "twist" and then "untwist" the coils. The wave so produced is a
None of these choices are correct
A bar magnet and an electrically polarized object are placed next to each other on a table. What happens?
Nothing happens
You see a positively charged helium ion in space, and it is at rest with respect to your spacecraft. Since you are studying for the final exam, you decide to experiment. You slowly push the N pole of a bar magnet closer to the helium ion. What happens to the helium ion?
Nothing happens, because the ion is not moving
The scientist credited with discovering that electric currents produce magnetic fields was
Oersted
Two long bar magnets lying on a table with their south poles facing each other exert a force of 45 N on each other. If the distance between these two poles is tripled, what is the new value of this force?
Poles tripled means it decreases by a factor of 9 45/9 = 5N
Which of the following types of radiation diffracts most when it passes through a diffraction grating?
Red
What would happen if you had a car made completely of plastic, with no metal parts, and you drove over a vehicle sensor embedded in the road surface?
The sensor would not notice you or your vehicle, and you'd be stuck at the red light
A bar magnet is broken in half and the magnetic field around one piece is mapped out. What is wrong with this picture?
There is no south pole
A loop of wire is oriented in the magnetic field as shown (the plane of the loop is perpendicular to the direction of the magnetic field and the magnetic field strength increases with height). Which of the following is true?
There will be an induced current if the loop is moved either up or down
In outer space, you observe a straight stream of electrons flowing past you at 14.5 miles per second, about the same speed that Mars moves on its orbit around the sun. You maneuver your spacecraft to face the current so that the electrons are moving from left to right and so that you are 10 m from the stream. Now you fire your rockets and boost your speed so that you are also moving at 14.5 miles per second, exactly at the same speed and direction as the electrons. In what direction does a compass needle point now?
You observe no magnetic field
A harmonic wave has
a close correspondence to simple harmonic motion
A positively charged ping pong ball is sitting stationary on the floor in the center of a room. There is also a constant, uniform magnetic field in the room that points toward the ceiling. If I now start the ball rolling toward the back of the room, the resultant motion of the ball, as observed from the ceiling, will be
a horizontal, clockwise circle.
Which of the following is a longitudinal wave?
a sound wave in a gas
The light from an incandescent bulb is composed of
all wavelengths in the visible portion of the electromagnetic spectrum
A current flowing through a long, straight wire causes a magnetic field that points
along concentric circles around the wire.
The magnetic pole near the Earth's north geographic pole actually has to be
an S pole, because it attracts the N pole of your compass needle.
Two identical coils of wire are placed on a single horizontal wooden broom handle. The coils are separated by a few centimeters. We now run identical currents in the same direction through each coil. The coils experience
an attractive magnetic force.
We visualize the magnetic field of the Earth by imagining that there is a bar magnet inside the Earth. Why did we draw this magnet with its south pole pointing north?
because the South Magnetic Pole of the Earth attracts North-seeking magnets, which is in the geographic North pole magnetic poles
The magnetic field lines of a bar magnet
begin on a north pole and end on a south pole.
A horizontal loop of wire has a magnetic field passing upwards through the plane of the loop. If this magnetic field increases with time, in what direction is the induced current predicted by Lenz's law?
clockwise as viewed from above
The south pole of a bar magnet is moved toward an aluminum ring, along the axis of the ring. As the magnet approaches, the changing magnetic flux induces an electric current in the ring that, when seen from the bar magnet, corresponds to positive charge carriers flowing
clockwise.
Two coils of wire are identical except that coil A has twice as many turns of wire as coil B. If a magnetic field increases with time at the same rate through both coils, which coil, if either, has the larger induced voltage?
coil A
A current-carrying rectangular loop of wire is placed in an external magnetic field with the directions of the current and field as shown in the diagram. In what direction will this loop tend to rotate as a result of the magnetic torque exerted on it?
counterclockwise
The force between two unlike magnetic poles
decreases as the square of the separation distance between them.
When a wave crosses from one medium into another in which the wave speed is lower, the frequency is unchanged. The wavelength
decreases.
Imagine that this classroom contains a constant magnetic field that points from the front to the back. In front of you a negative charge is slowly moving horizontally to your left. As you watch, the magnetic force on the charge
deflects the charge into a counterclockwise vertical circle.
A circular loop of wire whose plane is horizontal and that carries a current in a clockwise direction. If we were to represent the loop as a bar magnet or magnetic dipole, in what direction would the North pole be pointing?
downwards
A uniform magnetic field is directed horizontally toward the north, and a positive charge is moving west through this magnetic field. In what direction, if at all, is the magnetic force on the particle?
downwards
If we look down at the top of a circular loop of wire whose plane is horizontal and that carries a current in a clockwise direction, what is the direction of the magnetic field at the center of the circle?
downwards
A musical tone is coming from a loudspeaker. If a second loudspeaker nearby were to start playing exactly the same tone, the sound would
get louder in some areas and get softer in others.
As a wave passes from one medium into another, it often happens that its speed increases with no change in frequency. Under these circumstances, the wavelength
increases
If an electron moves in a magnetic field,
it only feels a force if its velocity vector is not parallel (or antiparallel) to the direction of the magnetic f
Since the magnetic fields of a coil of wire and a bar magnet are identical, are there current carrying loops inside natural magnetic materials?
no, each atom has electrons orbiting, and each electrons has a magnetic spin
A magnet on a frictionless mount would have its magnetic north pole point toward the Earth's geographic
north pole.
How many poles can a bar magnet have?
only two poles
In the southern hemisphere, the north pole of a compass needle
points away from the south geographic pole because there is a north magnetic pole there.
Two parallel wires, each carrying a current of 5.3 A, exert a force per unit length of 1.88×10−5 N/m on each other. What is the distance between the wires in centimeters?
r=2×(1×10−7 N/A2)×5.3 A×5.3 A / 1.88×10−5 N/m ×100 cm/m r=29.883 cm
The south pole of a bar magnet is moved toward a short helical coil of wire (solenoid) along the axis of the coil. The coil has 100 turns and the ends of the coil are connected to form a closed circuit. If the coil is replaced with a single loop of the same type of wire, and the magnet is moved exactly as before, the magnet experiences a force that is
repulsive and 100 times smaller.
A horizontal wire is oriented along an east-west line, and a compass is placed above it. How, if at all, will the compass needle deflect if the current flows through the wire?
the compass will be undisturbed by the current being turned on
You could use two parallel wires to move objects 1 and 2 apart if each wire is embedded in its own object and if
the currents in the wires are in opposite directions.
When a wave reflects from a stationary boundary,
the frequency is unchanged
An ideal transformer is used to either increase or decrease the voltage in an AC circuit. When the output voltage is greater than the input voltage of a transformer then
the power output is the same as the power input.
According to Faraday's Law of Electromagnetic Induction, the induced voltage is equal to
the rate of change of the magnetic flux.
Two waves approach each other as shown. When they completely overlap, the resulting wave will look like (image is a square looking wave running into a triangle looking wave)
the waves make a house looking wave when they collide into each other.
In outer space, you observe a straight stream of electrons flowing past you at 14.5 miles per second, about the same speed that Mars moves on its orbit around the sun. You maneuver your spacecraft to face the current so that the electrons are moving from left to right and so that you are 10 m from the stream. In what direction does a compass needle point?
up
Under which conditions are inductive detectors more effective than simple timer systems?
when the traffic varies with time of day and other factors
Does a compass needle always point directly towards the magnetic south pole?
yes, in the absence of any other strong magnetic field
In a transformer the equation relating the ratio of the voltage in the secondary to the voltage in the primary and the ratio of the number of turns in the secondary to the number of turns in the primary is
ΔV2 / ΔV1 = N2 / N1
A loop of wire enclosing an area of 0.23 m^2 has a magnetic field passing through its plane at an angle to the plane. The component of the field perpendicular to the plane is 0.12 T, and the component parallel to the plane is 0.05 T. What is the magnetic flux through this coil? The magnetic flux through the coil is_____T·m^2
Φ=(0.12 T)×0.23 m^2 Φ=0.0276 T⋅m^2
A coil of wire with 120 turns and a cross-sectional area of 0.12 m2 lies with its plane perpendicular to a magnetic field of magnitude 1.8 T. The coil is rapidly removed from the magnetic field in a time of 0.4 s. What is the initial magnetic flux through the coil? The initial magnetic flux through the coil is____ T·m^2. The average value of the voltage induced in the coil is ____V.
Φ=120×1.8 T×0.12 m^2 Φ=25.92 T⋅m^2 (25.92 − 0) T⋅m^2 / 0.4 s ε=64.8 V
