Physics Test #2
In radio transmission a radio wave serves as a carrier wave, and the sound signal is superimposed on the carrier wave. In amplitude modulation (AM) radio, the amplitude of the carrier wave varies according to the sound wave. The U.S. Navy sometimes uses flashing lights to send Morse code between neighboring ships, a process that has similarities to radio broadcasting. (a) Is this process AM or FM? (b) What is the carrier frequency? (c) What is the signal frequency? (d) What is the broadcasting antenna? (e) What is the receiving antenna?
ASK PERRY
When the switch in the figure is closed, a current is set up in the coil and the metal ring springs upward. Explain.
ASK PERRY!
39. Which condition of motion must be met with regard to a charged particle if it is in the process of emitting electromagnetic radiation? -Moves at constant velocity -Accelerates -Moves at the speed of light -Moves parallel to the uniform magnetic field
Accelerates
42. Microwave radiation is useful in which of the following? -Sending phone messages -Cooking food -Aircraft navigation -All
All of the above
A magneto is used to cause the spark in a spark plug in many lawn mowers today. A magneto consists of a permanent magnet mounted on a flywheel so that it spins past a fixed coil. Explain how this arrangement generates a large enough potential difference to cause the spark.
As the magnet moves at a high speed past the fixed coil , the magnetic flux through the coil changes rapidly, increasing as the magnet approaches the coil and decreasing as the magnet moves away. This rapid change in the flux gives large emf, large enough to cause a spark across the gap in the spark plug.
36. Resonance occurs in an AC series circuit when which of the following conditions is met? -Resistance equals capacitive reactance -Resistance equals inductive reactance -Capacitive reactance inductive reactance -Capacitive reactance equals zero
Capacitive reactance inductive reactance
26. A double loop a wire (making 2 turns) is in the x-y plane centered at the origin. A uniform magnetic field is increasing at a constant rate in the positive z-direction. Viewed from the positive z-axis, in which direction is the induced magnetic field in the loop? -in the positive z-direction -in the negative z-direction -there is no induced field because of the double loop -There is no induced field because the rate of the change of the magnetic field is constant.
in the negative z-direction
11. Electrical charges and magnetic poles have many similarities, but one difference is: -Opposite magnetic poles repel. -One magnetic pole cannot create magnetic poles in other materials -A magnetic pole cannot be isolated -Magnetic poles do not produce magnetic fields
A magnetic pole cannot be isolated
13. The magnetic pole of the Earth nearest to the geographic North Pole corresponds to which of the following? -A magnetic north pole -A magnetic south pole -A magnetic arctic pole -A magnetic Antarctic pole
A magnetic south pole
29. The function of the electric motor is which of the following conversion processes? -Mechanical energy to electrical -Electrical energy to mechanical -Low voltage to high or vice versa -Alternating current to direct
Electrical energy to mechanical
37. An ideal transformer is one that: -Has a turn ratio, N2/N1, equal to 1 -Works with direct current -Experiences no power loss -Has an output frequency of 60 Hz
Experiences no power loss
19. A current in a long, straight wire produces a magnetic field. The magnetic field lines: -Go out from the wire to infinity -Come in from infinity to the wire -Form circles that pass through the wire -Form circles that go around the wire.
Form circles that go around the wire.
38. Which of the following scientists first built and operated devices that could emit and detect man-made electromagnetic radiation? -Hertz -Ampere -Maxwell -Lenz
Hertz
Wearing a metal bracelet in a region of strong magnetic field could be hazardous. Discuss this statement.
If for some reason the magnetic field changed rapidly, then there would be an EMF that would be induced in the bracelet. The EMF would induced a current which would cause the bracelet to become hot. Which could lead to you getting burned.
Two charged particles are projected in the same direction into the magnetic field perpendicular to their velocities. if the two particles are deflected in opposite directions, what can you say about them?
If they are projected in the same direction into the same magnetic field, the charges are of opposite sign. The direction of the force depends on the sign of the charge, so you can ensure that both charges are of opposite sign.
Why should an infrared photograph of a person look different from a photograph taken using a visible light?
In visible light photograph you can see the colours but infrared works on heat signatures. It shows different colors on the amount heat of the object its capturing therefore infrared cameras are also used to search people covered by something. visible light cannot penetrate any opaque thing but infrared due to large wavelength penetrates it and can be see through cameras.
43. Temperature variation of different parts of a person's body can be detected by analyzing the emission pattern of which time of electromagnetic radiation? -Microwave -Infrared -Ultraviolet -X rays
Infrared
45. Of the various types of electromagnetic radiation, which is the most penetrating through all forms of matter? -Infrared -Gamma -Visible light -Ultraviolet
Infrared
40. In order of increasing frequency, which of the following is correct? -Visible, radio, ultraviolet, and x ray -Infrared, visible, ultraviolet, and gamma -Visible, gamma, ultraviolet, and x ray -Infrared, x ray, visible, and gamma
Infrared, visible, ultraviolet, and gamma
20. Consider two long, straight parallel wires, each carrying a current I. If the currents are flowing in opposite directions: -The two wines will attract each other -The two wires will repel each other -The two wires will except a torque on each other -Neither wire will exert a force on the other.
The two wires will repel each other
Why is the sum of maximum voltages across each of the elements in a series RLC circuit usually greater than the maximum applied voltage? Doesn't this violate Kirchhoff's loop rule?
The voltages are not added in a scalar form, but in a vector form, as shown in the phasor diagrams throughout the chapter. Kirchhoff's loop rule is true at any instant, but the voltages across different circuit elements are not simultaneously at their maximum values. Do not forget that an inductor can induce an emf in itself and that the voltage across it is 90° ahead of the current in the circuit in phase.
25. A straight wire of length l is oriented east-west and is in a magnetic field B pointing north. The wire is moving downward at a constant speed v. Which end of the rod is positively charged? -Neither -The east end -The west end -Both ends
The west end
22. A sensitive ammeter is connected to a wire loop and placed within the magnetic field of a strong horseshoe magnet. The ammeter shows a deflection when: -The wire is moved parallel to the field -The wire is moved perpendicularly to the field -Neither wire nor magnet is moving -The wire axis is parallel to the field
The wire is moved perpendicularly to the field
14. Assume that a uniform magnetic field is directed into this page. If an electron is released with an initial velocity directed from the bottom edge to the top edge of the page, which of the following describes the direction of the resultant force acting on the electron? -Out of the page -To the right -To the left -Into the page
To the right
41. Glass panes are opaque to certain type of radiation, which passes through quartz. What type of radiation is it? This radiation is important in ozone layer reactions. -Microwave -Gamma -X ray -Ultraviolet
Ultraviolet
How can a current loop be used to determine the presence of a magnetic field in a given region of space?
We are gonna put current in the loop, it is rotes then there is an external magnetic field. The loop can be mounted on an axle that can rotate . The curent loop will rotate when placed in an external magnetic field for some arbitrary orientation of the field relative to the loop . As the current in the loop is increased the torque on it will increase.
A circular loop is located in a uniform and constant magnetic field. Describe how an emf can be induced in the loop in this situation.
When you move the loop or the shape, you will change the flux (how much magnetic field is going through) and that causes the EMF to be induced.
Does the phase angle in a RLC series depend on frequency? What is the phase angle for the circuit when the inductive reactance equals the capacitance reactance?
Yes and 0
30. In a circuit made up of inductor, resistance, ammeter, battery, and switch in series, at which of the following times after the switch is closed is the rate of current increase greatest? -zero -one time constant -reciprocal of one time constant -ten time constants
Zero
35. The power dissipated in an AC series circuit increases as the phase angle approaches what value? -Zero -45 degrees -90 degrees -180 degrees
Zero
33. In an RCL circuit, the maximum current is 1 amp. What is the average current? -Square root of 2 * A -(1/square root of 2) *A -(1/2)A -None
(1/square root of 2) *A
21. Solenoid #1 has a length of L, cross sectional area A, and N turns. Solenoid #2 has a length 2L, cross-sectional area 2A, and 2N turns. Which solenoid has the greater magnetic field at its center when equal currents are going through them? -#1 -#2 -Both have the same magnetic field -Since it depends on the values of A and L, none of the above are correct.
Both have the same magnetic field
12. The magnetic field of the Earth is believed responsible for which of the following ? -Deflection of both charged and unchanged cosmic rays -Deflection of charged cosmic rays -Ozone in the upper atmosphere -Solar flares
Deflection of charged cosmic rays
31. How is the energy stored in a current-carrying inductor related to its self-inductance, L? -Directly proportional to L^2 -Directly proportional to L^1/2 -Directly proportional to L -Inversely proportional to L
Directly proportional to L
16. A wave is lying horizontally in the north-south direction and the horizontal magnetic field is toward the east. The current flows North. The direction of the fore on the wire will be: -East -Down, into the page -Up, out of the page -There is none
Down, into the page
What is the advantage of transmitting power at high voltages?
It is far more economical to transmit power at a high voltage than at a low voltage because I^2R the loss on the transmission line is significantly lower at high voltage. Transmitting power at high voltage permits the use of step-down transformers to make "low" voltages and high currents available to the end user. The advantage of transmitting power at high voltage is that it reduces power loss due to resistance in conductor. Power is dissipated as heat. Power loss is directly proportional to I2 as P=I2R. As voltage increases, current is decreased which reduces power loss. Due to less I2R loss, efficiency of transformer increases.
A hanging slinky toy is attached to a powerful battery and switch. When the switch is closed that the toy now carries current, does the slinky compress or expand?
It is going to compress because it is going to act as a magnet due to the coil acting as a current loop. The current running through it is what is causing it to have a magnetic field.
34. In a 60-Hz RLC circuit, the phase angle is positive. The values of the resistance, inductance, and the capacitance are no doubled. Which of the following is now true about the phase angle? -It is still positive -It could be zero -It will be negative -It could be positive, negative, zero, but it cannot be greater than its original value
It is still positive
17. In a mass spectrometer, an ion will have a smaller radius for its circular path if: -Its speed is greater -Its mass is greater -Its charge is greater -Magnetic field is weaker
Its charge is greater
32. In a capacitor in an AC circuit, the voltage: -Leads the current by 90 degrees -Lags the current by 90 degrees -May leas or lag the current depending on the frequency -Is in the phase with 70.7% of the current
Lags the current by 90 degrees
28. The basic function of the electric generator is which of the following conversion processes? -Mechanical energy to electrical -Electrical energy to mechanical -Low voltage to high or vice versa -Alternating current to direct
Mechanical energy to electrical
A bar magnet is dropped toward a conducting ring lying on the floor. As the magnetic falls toward the ring, does it move as a freely falling object? Explain.
No, when the bar magnet falls toward the loop, the changing magnetic field through the loop induces a current in the loop. That creates magnetic field. Since the current is being creating in the loop., the magnetic field will be different causing the object to fall slower.
15. A stationary postive charge +Q is locked in a magnetic field B, which is directed toward the right as indicated. The direction of the magnetic force on Q is -Toward the right -Up -Down -None
None
44. As an electromagnetic wave travels through free space, its speed can be increased by: -Increasing its frequency -Increasing its energy only -Increasing both its energy and momentum -None of the above will increase its speed
None of the above
18. Magnetism had been a known phenomenon for some time before its relation to electric currents was found. That a current in a wire produces a magnetic field was discovered by: -Maxwell -Ampere -Oersted -Tesla
Oersted
23. According to Lenz's law the direction of an induced current in a conductor will be that which tends to produce which of the following effects? -Enhance the effect which produces it -Produce a greater heating effect -Produce the greatest voltage -Oppose the effect which produces it
Oppose the effect which produces it
The Doppler shift for electromagnetic radiation from distant glaxies moving away from the observer is called a: -Red shift -Blue shift -Black shift -Vacuum shift
Red shift
27. Three loops of wire, one circular, one rectangular, and one square, are made from identical lengths of wire. If the loops are in the same increasing magnetic field perpendicular to the plane of the child, which loop has the greatest induced emf? -The circular one -The rectangular one -The square one -All three would have the same emf induced
The circular one
24. A coil is placed in a changing magnetic field and an emf is induced. What happens to the induced emf if the rate of change of magnetic field quadruples? -There is no change -The emf doubles -The emf quadruples -The emf increases by a factor of 16
The emf quadruples
How can motions of a charged particle be used to distinguish between a magnetic field and an electric field in a certain region? Give a specific example to justify.
The magnetic force on a moving charged particle is always perpendicular to the particle's direction of motion. There is no magnetic force on the charge when it moves parallel to the direction of the magnetic field. For an electric field, the force is never 0 and is always parallel. Therefore, by projecting the charged particle in different directions, it is possible to determine the nature of the field.