AP/IB Review Guide CH20-21

Multiple ChoiceIdentify the choice that best completes the statement or answers the question.

____ 1. The units T·m2/s are equivalent to:a.

W.

b.

V.

c.

N/m.

d.

webers.

e.

F

____ 2. 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:a.

the wire is moved parallel to the field.

b.

the wire is moved perpendicularly to the field.

c.

neither wire nor magnet is moving.

d.

the wire's axis is parallel to the field.

e.

the wire's axis is perpendicular to the field.

____ 3. 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?a.

enhance the effect which produces it

b.

produce a greater heating effect

c.

produce the greatest voltage

d.

oppose the effect which produces it

e.

produce the greatest magnetic field

____ 4. A bar magnet is falling through a loop of wire with constant velocity. The south pole enters first. As the magnet leaves the wire, the induced current (as viewed from above):a.

is clockwise.

b.

is counterclockwise.

c.

is zero.

d.

is along the length of the magnet.

e.

More information is needed.

____ 5. A metal rod is falling toward the surface of the Earth near the equator. As it falls, one end of the rod becomes positively charged due to the motional emf of the rod through the Earth's magnetic field. The rod is oriented so that:a.

the rod is vertical with the positive end higher.

b.

the rod is horizontal with the positive end toward the north.

c.

the rod is horizontal with the positive end toward the east.

d.

the rod is horizontal with the positive end toward the west.

e.

the rod is horizontal with the positive end toward the south.

____ 6. A straight wire of length is oriented east-west and is in a magnetic field B pointing north. The wire is moving downward at a constant speed v. If the resistance of the rod is R, what is the current through the rod?a.

R/B lv

b.

B v/R

c.

B2 2v2/R2

d.

B v/R2

e.

not given

____ 7. The rate of heat dissipation in an AC circuit with resistance, R, and effective current, Irms, is given by which of the following?a.

0.5 × (Irms)2R

b.

(Irms)2R

c.

2.0 × (Irms)2R

d.

4.0 × (Irms)2R

e 0.25 × (Irms)2R

.

____ 8. The rms current is equal to the direct current that:a.

produces the same average voltage across a resistor as in an AC circuit.

b.

dissipates an equal amount of energy in a resistor at the same rate as in an AC circuit.

c.

provides the same average current in a resistor as in an AC circuit.

d.

results in the same peak power in a resistor as in an AC circuit.

e.

produces the same peak voltage across a resistor as in an AC circuit.

____ 9. An ideal transformer is one that:a.

has a turn ratio, N2/N1, equal to 1.

b.

works with direct current.

c.

experiences no power loss.

d.

has an output frequency of 60 Hz.

e.

works with alternating current.

____ 10. In order of increasing frequency, which of the following is correct?a.

visible, radio, ultraviolet and x-ray

b.

infrared, visible, ultraviolet and gamma

c.

visible, gamma, ultraviolet and x-ray

d.

infrared, x-ray, visible and gamma

e.

infrared, visible, ultraviolet and radio

____ 11. In order to keep its food hot, a restaurant will place it under which type of lamp?a.

infrared

b.

visible light

c.

ultraviolet

d x-ray

.e.

gamma

____ 12. Glass panes are opaque to a certain type of radiation, which passes through quartz. What type of radiation is it? This radiation is important in ozone layer reactions.a.

microwave

b.

gamma

c.

x-ray

d.

ultraviolet

e.

radio

____ 13. Microwave radiation is useful in which of the following?a.

sending phone messages

b.

cooking food

c.

aircraft navigation

d.

medical applications

e.

All of the above are valid choices.

____ 14. Temperature variation of different parts of a person's body can be detected by analyzing the emission pattern of which type of electromagnetic radiation?a.

microwave

b.

infrared

c.

ultraviolet

d.

x-rays

e.

gamma

____ 15. Of the various types of electromagnetic radiation, which is the most penetrating through all forms of matter?a.

infrared

b gamma

.c.

visible light

d.

ultraviolet

e.

x-rays

____ 16. As an electromagnetic wave travels through free space, its speed can be increased by:a.

increasing its frequency.

b.

increasing its energy only.

c.

increasing both its energy and momentum.

d.

decreasing its frequency

e.

None of the above will increase its speed.

____ 17. An object that is giving off only infrared electromagnetic waves is giving off heat through:a.

convection.

b.

conduction.

c.

radiation.

d.

visible light.

e.

emission of electrons.

____ 18. The electromagnetic radiation that causes tanning:a.

can produce cancer.

b.

rarely passes through glass windows.

c.

is absorbed by ozone.

d.

is all of the above.

e.

is none of the above.

____ 19. In the Doppler effect for electromagnetic waves, which of the following gives the greatest shift in frequency?a the source moving toward the non-moving observer at speed v

.b.

the observer moving toward the non-moving source at speed v

c.

the source moving toward the approaching observer, both at speed v/2

d.

All of the above give the same shift.

____ 20. The Doppler shift for electromagnetic radiation from distant galaxies moving away from the observer is called a:a.

red shift.

b.

blue shift.

c.

black shift.

d.

vacuum shift.

e.

radiation shift.

Short Answer

21. A uniform 4.5-T magnetic field passes perpendicularly through the plane of a wire loop 0.10 m2 in area. What flux passes through the loop?

22. A uniform 4.5-T magnetic field passes through the plane of a wire loop 0.10 m2 in area. What flux passes through the loop when the direction of the 4.5-T field is at a 30° angle to the normal of the loop plane?

23. A loop of area 0.250 m2 is in a uniform 0.020 0-T magnetic field. If the flux through the loop is 3.83 × 10-3 T·m2, what angle does the normal to the plane of the loop make with the direction of the magnetic field?

24. A coil in a magnetic field encloses a flux of 0.256 T·m2 when the angle between the normal to the coil and the direction of the magnetic field is 70.0°. What flux would go through the coil if the angle were changed to 40.0°?

25. A coil is placed in a magnetic field and has a flux ΦB through it. The coil is stressed so that its area reduces to 75% of its original value. If the plane of the coil stays the same and the flux through it remains the same, how must the magnetic field change?

26. "GFI" stands for:

27. The principle or law that says "an induced emf in a circuit loop produces a current whose magnetic field opposes further change of magnetic flux" is credited to:

28. A square coil, enclosing an area with sides 2.0 cm long, is wrapped with 2 500 turns of wire. A uniform magnetic field perpendicular to its plane is turned on and increases to 0.25 T during an interval of 1.0 s. What average voltage is induced in the coil?

29. A 10-turn square coil of area 0.036 m2 and a 20-turn circular coil are both placed perpendicular to the same changing magnetic field. The voltage induced in each of the coils is the same. What is the area of the circular coil?

30. A flat coil of wire consisting of 20 turns, each with an area of 50 cm2, is positioned perpendicularly to a uniform magnetic field that increases its magnitude at a constant rate from 2.0 T to 6.0 T in 2.0 s. If the coil has a total resistance of 0.40 Ω, what is the magnitude of the induced current?

31. A planar loop consisting of four turns of wire, each of which encloses 200 cm2, is oriented perpendicularly to a magnetic field that increases uniformly in magnitude from 10 mT to 25 mT in a time of 5.0 ms. What is the resulting induced current in the coil if the resistance of the coil is 5.0 Ω?

32. 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?

33. A 0.200-m wire is moved parallel to a 0.500-T magnetic field at a speed of 1.50 m/s. What emf is induced across the ends of the wire?

34. An airplane with a wingspan of 60.0 m flies parallel to the Earth's surface at a point where the downward component of the Earth's magnetic field is 0.400 × 10−4 T. If the induced potential between wingtips is 0.900 V, what is the plane's speed?

35. A large jetliner with a wingspan of 40 m flies horizontally and due north at a speed of 300 m/s in a region where the magnetic field of the earth is 60 µT directed 50° below the horizontal. What is the magnitude of the induced emf between the ends of the wing?

36. A straight wire of length 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?

37. What is she effective (rms) current value for an AC current with an amplitude of 10 A?

38. In an AC series circuit, the current in a pure resistor differs in phase with the applied voltage by what angle?

39. An AC voltage source, with a peak output of 200 V, is connected to a 50-Ω resistor. What is the effective (or rms) current in the circuit?

40. An AC voltage source, with a peak output of 200 V, is connected to a 50-Ω resistor. What is the rate of energy dissipated due to heat in the resistor?

41. An AC voltage source, with a peak output of 120 V, results in dissipation of energy in a resistor at rate of 100 W. What is the value of the resistance?

42. The peak voltage of an AC source is 200 V. What is the rms voltage?

43. In the typical household AC voltage of 120 V, what is the peak voltage?

44. The primary winding of an electric train transformer has 400 turns and the secondary has 50. If the input voltage is 120 V(rms), what is the output voltage?

45. A transformer consists of a 500-turn primary coil and a 2 000-turn secondary coil. If the current in the secondary is 3.00 A, what is the primary current?

46. An AC power generator produces 50 A (rms) at 3 600 V. The voltage is stepped up to 100 000 V by an ideal transformer and the energy transmitted through a long-distance power line with a total resistance of 100 Ω. What is the rms current in the long-distance line?

47. An AC power generator produces 25 A (rms) at 3 600 V. The energy is transmitted through a long-distance power line, which has a total resistance of 100 Ω. What percentage of the power delivered by the generator is dissipated as heat in the long-distance line if a step-up transformer is not used?

48. A transformer is to be designed to increase the 30-kV (rms) output of a generator to the transmission line voltage of 345 kV (rms). If the primary winding has 80 turns, how many turns must the secondary have?

49. A radar pulse returns 3.0 × 10−4 seconds after it is sent out, having been reflected by an object. What is the distance between the radar antenna and the object? (c = 3.00 × 108 m/s)

50. A radio wave signal, which transmits at a frequency of 7.20 MHz, has what wavelength? (c = 3.00 × 108 m/s)

51. A radar pulse sent out to an airplane at a distance of 20.0 km will return as an echo to the source in what time interval? (c = 3.00 × 108 m/s)

52. The human eye is sensitive to light with wavelength down to 390 nm. What is the frequency of radiation at this wavelength? (1 nm = 10−9 m and c = 3.00 × 108 m/s)

53. An ultraviolet light wave has a wavelength of 300 nm and speed of 2.1 × 108 m/s through a transparent medium. What is the frequency of this wave in the medium? (1 nm = 10−9 m and c = 3.00 × 108 m/s)

54. What value of inductance should be used in a series circuit with a capacitor of 1.8 × 10−3 µF when designed to radiate a wavelength of 35 m? (c = 3.00 × 108 m/s)

55. What is the wavelength of 100-MHz television EM waves? (c = 3 × 108 m/s)

56. Find the frequency of x-rays of wavelength 10−10 m. (c = 3 × 108 m/s)

57. An observer is moving in space toward a distant star at 100 km/s while the star is moving toward the observer at 200 km/s; the relative velocity being 300 km/s of approach. What is the relative change in frequency of the light from the star as seen by the observer? (The speed of light in space is 3.00 x 105 km/s.)

AP/IB Review Guide CH20-21Answer Section

MULTIPLE CHOICE

1. B

2. B

3. D

4. B

5. C

6. E

7. B

8. B

9. C

10. B

11. A

12. D

13. E

14. B

15. B

16. E

17. C

18. D

19. D

20. A

SHORT ANSWER

21. 0.45 T×m2

22. 0.39 T×m2

23. 40.0°

24. 0.573 T·m2

25. It must increase by 33%.

26. ground fault interrupter.

27. Lenz.

28. 0.25 V

29. 0.018 m2

30. 500 mA

31. 48 mA

32. The emf quadruples.

33. 0.150 V

34. 375 m/s

35. 550 mV

36. the east end

37. 7.1 A

38. zero

39. 2.8 A

40. 400 W

41. 72 Ω

42. 141 V

43. 170 V

44. 15 V

45. 12.0 A

46. 1.8 A

47. 69%

48. 920

49. 4.5 × 104 m

50. 41.7 m

51. 133 × 10−6 s

52. 7.7 × 1014 Hz

53. 7.0 × 1014 Hz

54. 1.9 × 10−4 mH

55. 3 m

56. 3 × 1018 Hz

57. 0.10% increase