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physics
college physics a strategic approach 2nd
College Physics Essentials Electricity And Magnetism Optics Modern Physics Volume Two 8th Edition Jerry D. Wilson, Anthony J. Buffa, Bo Lou - Solutions
11. Why is dispersion more prominent when using a triangular prism rather than a square block?
10. Both refraction and dispersion are caused by the difference in the speed of light. What is the difference in the physical cause (reason)?
#!# angle of incidence is always greater than the angle of refraction. Could total internal reflection take place from medium 1 to medium 2? Explain.
9. When light enters medium 2 from medium 1, the
8. If total internal reflection is taking place between two transparent materials, what can you conclude about the indices of refraction of the two materials? How about the angle of incidence?
7. Explain why the pencil in ▶ Figure 22.25 appears almost severed. Also, compare this figure with Figure 22.15b and explain the difference.
6. As light travels from one medium to another, does its wavelength change? Its frequency? Its speed?
5. Two hunters, one with a bow and arrow and the other with a laser gun, see a fish under water. They both aim directly for the location where they see the fish. Does the arrow or the laser beam have a better chance of hitting the fish? Explain.
4. It is sometimes difficult to read magazines using highgloss paper due to glare. Why?
3. After rain, what kind of reflection can take place off of the road surface?
2. The book you are reading is not itself a light source, so it must be reflecting light from other sources. What type of reflection is this?
1. Under what circumstances is the angle of reflection not equal to the angle of incidence?
10. Dispersion is caused by (a) the difference in the speed of light in different media, (b) the difference in the speed of light for different wavelengths of light in a given medium, (c) the difference in the angle of incidence for different wavelengths of light in a given medium, (d) the
9. Dispersion can occur only during (a) specular reflection,(b) diffuse reflection, (c) refraction, (d) total internal reflection.
8. Dispersion can occur only if the light is (a) monochromatic,(b) polychromatic, (c) white light, (d) both b and c.
7. Which of the following must be satisfied for total internal reflection to occur: (a) n1 > n2, (b) n2 > n1,(c) θ1 > θc, or (d) θc < θ1?
6. The index of refraction (a) is always greater than or equal to 1, (b) is inversely proportional to the speed of light in a medium, (c) is inversely proportional to the wavelength of light in the medium, (d) all of the preceding.
5. Light refracted at the boundary of two different media(a) is bent toward the normal when n1 > n2, (b) is bent away from the normal when n1 > n2, (c) is bent away from the normal when n1 < n2, (d) has the same angle of refraction as the angle of incidence.
4. Refraction is caused by the fact that (a) different media have different speeds of light, (b) a given medium has different speeds of light for different wavelengths,(c) the angle of incidence is greater than the critical angle, (d) a given medium has different indices of refraction for different
3. For both specular (regular) and diffuse (irregular)reflections, (a) the angle of incidence equals the angle of reflection, (b) the incident and reflected rays are on opposite sides of the normal, (c) the incident ray, the reflected ray, and the local normal lie in the same plane, (d) all of the
2. The angle of reflection is the angle between (a) the reflected ray and the reflecting surface, (b) the incident ray and the normal to the surface, (c) the reflected ray and the incident ray, (d) the reflected ray and the normal to the reflecting surface.
1. A ray is (a) perpendicular to the direction of energy flow, (b) parallel to the direction of energy flow,(c) always parallel to other rays, (d) parallel to a series of wave fronts.
47. ••• A series RLC circuit has components with resistive/reactance values of: R = 50 Ω, L = 0.15 H, and C = 20 μF. The circuit is driven by a 120-V, 60-Hz source. (a) What is the current in the circuit, expressed as a percentage of the maximum possible current? (b) What is the power
46. ••• A series RLC circuit with a resistance of 400 Ωhas capacitive and inductive reactances of 300 and 500 Ω, respectively. (a) What is the power factor of the circuit? (b) If the circuit operates at 60 Hz, what additional capacitance should be connected to the original capacitance to
44. •• (a) In Exercises 42 and 43, determine the numerical(scalar) sum of the rms voltages across the three circuit elements and explain why it is larger than the source voltage. (b) Determine the sum of these voltages using the proper phasor techniques and show that your result is equal to the
43. •• A series RLC circuit has a resistance of 25 Ω, a capacitance of 0.80 μF, and an inductance of 250 mH.The circuit is connected to a variable-frequency source with a fixed rms voltage output of 12 V. If the source frequency is set at the circuit’s resonance frequency, what is the rms
42. •• A series circuit is connected to a 220-V, 60-Hz power supply. The circuit has the following components:a 10-Ω resistor, a coil with an inductive reactance of 120 Ω, and a capacitor with a reactance of 120 Ω.Compute the rms voltage across (a) the resistor,(b) the inductor, and (c) the
41. •• A small welding machine uses a voltage source of 120 V at 60 Hz. When the source is operating, it requires 1200 W of power, and the power factor is 0.75. (a) What is the machine’s circuit impedance?(b) Find the rms current in the machine while operating.
40. IE •• A coil with a resistance of 30 Ω and an inductance of 0.15 H is connected to a 120-V, 60-Hz source. (a) Is the phase angle of this circuit (1) positive,(2) zero, or (3) negative? Explain. (b) What is the phase angle of the circuit? (c) How much rms current is in the circuit? (d) What
39. •• A tuning circuit in a radio receiver has a fixed inductance of 0.50 mH and a variable capacitor.(a) If the circuit is tuned to a radio station broadcasting at 980 kHz, what is the capacitance value? (b) What value of capacitance is required to tune into a station broadcasting at 1280 kHz?
38. •• (a) What is the resonance frequency of an RLC circuit with a resistance of 100 Ω, an inductance of 100 mH, and a capacitance of 5.00 μF? (b) What is the resonance frequency if all the values in part (a) are doubled?
37. •• (a) How much power is dissipated in the circuit described in Exercise 36b using the initial values of resistance, inductance, and capacitance? (b) How much power is dissipated in the same circuit at resonance?
36. IE •• (a) A series RLC circuit is in resonance. Which one of the following can you change without upsetting the resonance: (1) resistance, (2) capacitance, (3) inductance, or (4) frequency? Explain. (b) A resistor, an inductor, and a capacitor have resistance/reactance values of 500 Ω, 500
35. IE •• In a series RLC circuit, R = XC = XL = 40 Ωat a certain driving frequency. (a) This circuit is(1) inductive, (2) capacitive, (3) in resonance. Explain your reasoning. (b) If the driving frequency is doubled, what will be the impedance of the circuit?
34. •• A series RLC circuit contains a resistance of 25 Ω, an inductance of 0.30 H, and a capacitance of 8.0 μF.(a) At what frequency should the circuit be driven for the maximum power to be transferred from the driving source? (b) What is the impedance at that frequency?
33. IE •• A series RC circuit has a resistance of 100 Ω and a capacitive reactance of 50 Ω. (a) Is the phase angle(1) positive, (2) zero, or (3) negative? Explain. (b) What is the phase angle of this circuit?
32. •• A series RC circuit has a resistance of 250 Ω and a capacitance of 6.0 μF. If the circuit is driven by a 60-Hz source, find (a) the capacitive reactance and(b) the impedance of the circuit.
31. •• A series RL circuit has a resistance of 100 Ω and an inductance of 100 mH. It is driven by a 120-V, 60-Hz source. (a) Find the inductive reactance and the impedance of the circuit. (b) What is the current is in the circuit?
30. •• A series RC circuit has a resistance of 200 Ω and a capacitance of 25 μF and is driven by a 120-V, 60-Hz source. (a) Find the capacitive reactance and impedance of the circuit. (b) What is the current is in the circuit?
29. • A coil in a 60-Hz circuit has a resistance of 100 Ωand an inductance of 0.45 H. Calculate (a) the coil’s reactance and (b) the circuit’s impedance.
28. IE •• An inductor is connected to a variable-frequency ac voltage source. (a) If the frequency decreases by a factor of 2, the rms current will be (1) 2, (2) 1/2,(3) 4, (4) 1/4 times the original rms current. Explain.(b) If the rms current in an inductor at 40 Hz is 9.0 A, what is its rms
27. •• A circuit with a single capacitor is connected to a 120-V, 60-Hz source. (a) What is its capacitance if there is a current of 0.20 A in the circuit? (b) What would be the current if the source frequency were halved?
26. •• (a) What inductance has the same reactance in a 120-V, 60-Hz circuit as a capacitance of 10 μF? (b) What would be the ratio of inductive reactance to capacitive reactance if the frequency were changed to 120 Hz?
25. •• A 150-mH inductor is in a circuit with a 60-Hz voltage source, resulting in a current of 1.6 A. (a) What is the rms voltage of the source? (b) What is the phase angle between the current and the source voltage?
24. IE •• A capacitor is connected to a variable-frequency ac voltage source. (a) If the frequency increases by a factor of 3, the capacitive reactance will be (1) 3, (2) 1/3, (3) 9,(4) 1/9 times the original reactance. Explain. (b) If the capacitive reactance of a capacitor at 120 Hz is 100
23. •• (a) Find the frequency at which a 250-mH inductor has a reactance of 400 Ω. (b) At what frequency would a 0.40 μF capacitor have the same reactance?
22. •• (a) An inductor has a reactance of 90 Ω in a 60-Hz ac circuit. What is its inductance? (b) What frequency would be required to double its reactance?
21. •• A variable capacitor in a circuit with a 120-V, 60-Hz source initially has a capacitance of 0.25 μF. The capacitance is then increased to 0.40 μF. (a) What is the percentage change in the capacitive reactance?(b) What is the percentage change in the current in the circuit?
20. •• A single 50-mH inductor is connected to an ac voltage source at 120 V and 60 Hz. (a) What is its inductive reactance? (b) What is the current in this circuit? (c) What is the phase angle between the current and applied voltage? (Assume negligible resistance.)
19. • How much current is in a circuit containing only a 50-μF capacitor connected to an ac generator with an output of 120 V and 60 Hz?
18. • What capacitance value would create a reactance of 100 Ω in a 60-Hz ac circuit?
17. • A single 2.0-μF capacitor is connected across the terminals of a 60-Hz voltage source, and a current of 2.0 ma results. What is the capacitive reactance of the capacitor?
16. • At what frequency does a 25-μF capacitor have a reactance of 25 Ω?
15. ••• The current in a resistor is given by I = (12.0 A)sin(380t). (a) What is the frequency of the current? (b) What is the rms current? (c) How much average power is delivered to the resistor? (d) Write an equation for the voltage across the resistor as a function of time. (e) Write an
14. •• The current and voltage outputs of an operating ac power supply have peak values of 2.5 A and 16 V, respectively. (a) What is the average power output of the generator? (b) What is the effective resistance of the circuit it is in?
13. •• The current in a resistor is given by I = (8.0 A)sin(40πt) when an ac voltage given by ΔV = (60 V)sin(40πt) is applied to it. (a) What is the resistance value? (b) What are the frequency and period of the voltage source? (c) What is the average power delivered to the resistor?
12. •• A 50-kW electric heater is designed to run using a 240-V ac source. Find its (a) peak current and (b) peak voltage. (c) How much energy will you be billed for in a 30-day month if it operates 2.0 h per day?
11. •• Find the rms and peak currents in a 40-W, 120-V lightbulb. What is its resistance?
10. •• What are the resistance, peak current, and power level of a computer monitor that draws an rms current of 0.833 A when connected to a 120-V outlet?
9. •• An ac voltage source has an rms voltage of 120 V. Its voltage goes from zero to its maximum positive value in 4.20 ms. Write an expression for the voltage as a function of time.
8. IE •• An ac voltage source has a peak voltage of 85 V and a frequency of 60 Hz. The voltage at t = 0 is zero.(a) If a student measures the voltage at t = 1/240 s, how many possible results are there: (1) one, (2) two, or (3) three? Why? (b) Determine all possible voltages the student might
7. •• An ac voltage is applied to a 25.0-Ω resistor so that it dissipates 500 W of power. Find the resistor’s(a) rms and peak currents and (b) rms and peak voltages.
6. IE •• The voltage across a resistor varies asΔV = (170 V)sin(100πt). (a) Is the current in the resistor (1) in phase with the voltage, (2) ahead of the voltage by 90°, or (3) lagging behind the voltage by 90°? (b) Write the expression for the current in the resistor as a function of time
5. • A hair dryer is rated at 1200 W when plugged into a 120-V outlet. Find (a) its rms current, (b) its peak current, and (c) its resistance.
4. • An ac circuit contains a resistor with a resistance of 5.0 Ω. The resistor has an rms current of 0.75 A.(a) Find its rms voltage and peak voltage. (b) Find the average power delivered to the resistor.
3. • How much ac rms current must be in a 10-Ω resistor to produce an average power of 15 W?
2. • An ac circuit has an rms current of 5.0 A. What is the peak current? What is the average current?
1. • What are the peak and rms voltages of a 120-V ac line and a 240-V ac line?
15. If a driven RLC circuit has an inductive reactance of 250 Ω and a capacitive reactance of 150 Ω, is the driving frequency exactly at, above, or below the circuit’s resonant frequency? Explain your reasoning.
14. An RLC circuit is driven by an ac voltage source and is at resonance. Then the driving frequency changes and the power output drops. Can you tell if the frequency increased or decreased? Explain.
13. For each of the following cases for an RLC circuit, does the resonance frequency increase, decrease, or stay the same? If it changes, tell by what factor.(a) Only the capacitance is changed – it is quadrupled.(b) Only the inductance is changed – it is increased by nine times. (c) Only the
12. An RLC circuit consists of a 25-Ω resistor, a 1.00-μF capacitor, and a 250-mH inductor. If it is driven by an ac voltage source whose frequency is 60 Hz, (a) what is the impedance of an RLC circuit at resonance?(b) How does its impedance compare to that in part (a) if the source frequency is
11. A capacitor is connected by itself to a 60-Hz ac voltage source. To ensure the circuit has the same capacitive reactance when the capacitor is replaced with one of twice the capacitance, would you decrease or increase the source frequency? By what factor should it change?Explain your reasoning.
10. An inductor is connected by itself to a 60-Hz ac voltage source. To ensure it has the same inductive reactance when it is connected to a 240-Hz source, would you decrease or increase its inductance value? By what factor should it change? Explain your reasoning.
9. The current in an ac circuit containing only an ac voltage source and a 10-μF capacitor is described by I = (2.0 A) sin(120πt + π/2). Explain why the instantaneous voltage across it at t = 0 is zero whereas the current at that time is not.
8. Can an inductor oppose dc current? What about a capacitor? Explain each and why they are different.
7. Explain why, under very low-frequency ac conditions, a capacitor acts almost as an open circuit while an inductor acts almost as a short circuit.
6. A 25-Ω resistor is wired directly across a 120-V ac source. What happens to the time-average power, rms voltage, and rms current when the ac source is changed to 240 V? Do their values increase, decrease, or remain the same? Explain.
5. A 25-Ω resistor is wired directly across a 120-V ac source. What happens to the time-average power, rms voltage, and rms current when the resistor’s value changes to 50 Ω? Do their values increase, decrease, or remain the same? Explain.
4. If the ac voltage and current for a particular circuit element are given by ΔV = (120 V)sin(120πt) and I = (30 A)sin(120πt), respectively, could the circuit element be a resistor? What is the frequency of the source?
3. A 60-W lightbulb designed to work at 240 V in England is instead connected to a 120-V source. Discuss the changes in the bulb’s rms current and power when it is at 120 V compared with 240 V. Assume the bulb is ohmic.
2. The voltage and current associated with a resistor in an ac circuit are in phase. What does that mean physically?
1. The average current in a resistor in an ac circuit is zero.Explain why the average power delivered to a resistor isn’t zero.
14. When a series RLC circuit is not driven at its resonance frequency, energy may be dissipated as joule heat in either the capacitor or the inductor. Is this statement(a) true, (b) false, or (c) cannot be determined from the given information?
13. When a series RLC circuit is driven at its resonance frequency, (a) energy is dissipated only by the resistive element, (b) the power factor has a value of one,(c) there is maximum power delivered to the circuit,(d) all of the preceding.
12. If the capacitance of a series RLC circuit is decreased,(a) the capacitive reactance increases, (b) the inductive reactance increases, (c) the current remains constant,(d) the power factor remains constant.
11. The impedance of an RLC circuit depends on(a) frequency, (b) inductance, (c) capacitance, (d) all of the preceding.
10. A single inductor is connected to an ac voltage source.When the current in the inductor is at a maximum, the voltage across the inductor is not changing. Is this statement (a) true, (b) false, or (c) cannot be determined from the given information?
9. A single inductor is connected to an ac voltage source.When the voltage across the inductor is at a maximum, the current in it is not changing. Is this statement (a)true, (b) false, or (c) cannot be determined from the given information?
8. A single capacitor is connected to an ac voltage source.When the current in the circuit is at a maximum, then the energy stored in the capacitor is (a) zero,(b) at a maximum, (c) neither of the preceding, but somewhere in between.
7. A single capacitor is connected to an ac voltage source. When the voltage across the capacitor is at a maximum, then the charge on it is (a) zero, (b) at a maximum, (c) neither of the preceding, but somewhere in between.
6. In a purely capacitive ac circuit, (a) the current and voltage are in phase, (b) the current leads the voltage,(c) the current lags behind the voltage, or (d) none of the preceding.
5. In ac operation in the United States, how much time elapses between successive maximum power values in a resistor: (a) 1/60 s, (b) 1/120 s, or (c) 1/30 s?
4. During five complete ac voltage cycles (in the United States) how many times does the power dissipation in a resistor reach its maximum: (a) once, (b) five times,(c) ten times, or (d) twice?
3. Over seven complete ac voltage cycles (in the United States) what is the average voltage: (a) 0 V, (b) 60 V,(c) 120 V, or (d) 170 V?
2. During one ac voltage cycle (in the United States) how long does the direction of the current stay constant in a resistor: (a) 1/60 s, (b) 1/120 s, or (c) 1/30 s?
1. Which of the following is true for a sinusoidally varying ac voltage: (a) ΔVm = ΔVrms, (b) ΔVm ≈ (0.707)ΔVrms,(c) ΔVrms ≈ (0.707)ΔVm, or (d) ΔVrms≈ (0.5)ΔVrms?
44. IE ••• Microwave ovens can have cold spots and hot spots due to standing electromagnetic waves, analogous to standing wave nodes and antinodes in strings (▼ Figure 20.23 shows such spots in the lasagna cheese topping – some melted, some not). (a) The longer the distance is between
43. •• A certain type of radio antenna is called a quarterwavelength antenna, because its length is equal to one-quarter of the wavelength to be received. If you were going to make such antennae for the AM and FM radio bands by using the middle frequencies of each band, what lengths of wire
42. •• Orange light has a wavelength of 600 nm, and green light has a wavelength of 510 nm. (a) What is the difference in frequency between these two types of light? (b) If you doubled the wavelength of both, what type of light would they become?
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