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physics
college physics a strategic approach 2nd

Questions and Answers of College Physics A Strategic Approach 2nd

23. Heating a permanent magnet can significantly reduce the magnetic field it produces. The reduction in field strength by this method is mainly due to (a) domain orientation change, (b) domain
22. When a ferromagnetic material is placed in an external magnetic field, (a) the domain orientation may change, (b) the domain boundaries may change,(c) new domains are created, (d) both (a) and
21. The main source of magnetism in magnetic materials is (a) electron orbits, (b) electron spin, (c) magnetic poles, (d) nuclear properties.
20. Consider a current-carrying circular loop of wire.On its central axis (that is, the line perpendicular to the area of the loop and passing through its center), which location has the least
19. A current-carrying loop of wire is in the plane of this paper. Outside the loop, its magnetic field points into the paper. What is the direction of the current in the loop: (a) clockwise, (b)
18. You are looking directly into one end of a long solenoid. The magnetic field at its center points directly away from you. What is the direction of the current in the solenoid, as viewed by
17. A long, straight wire is parallel to the ground and carries a steady current to the west. At a point directly below the wire, what is the direction of the magnetic field the wire produces: (a)
16. For the current-carrying loop shown in Figure 19.16, the maximum torque occurs for what value of the angle θ: (a) 0°, (b) 90°, (c) 180°, or (d) the torque is the same for all angles?
15. You are looking horizontally due west directly and perpendicularly at the circular plane of a currentcarrying coil. The coil is in a uniform vertically upward magnetic field. When released, the
14. A long, straight, horizontal wire located on the equator carries a current. In what direction should the current be if the purpose is to balance the wire’s weight with the magnetic force on it
13. A long, straight, horizontal wire located on the equator carries a current directed west. What is the direction of the force on the wire due to the Earth’s magnetic field:(a) east, (b) west,
9. In an ac generator, the maximum emf output occurs when the magnetic flux through the coil is (a) zero,(b) maximum, (c) not changing, (d) it does not depend on the flux in any way.
45. •• A solenoid is wound with 200 turns/cm. An outer layer of insulated wire with 180 turns/cm is wound over the first layer of wire. When the solenoid is operating, the inner coil carries a
44. •• A current-carrying solenoid is 10 cm long and is wound with 1000 turns of wire. It produces a magnetic field of 4.0 × 10−4 T at its center. (a) How long would the solenoid have to be to
43. •• A circular loop of wire of radius 5.0 cm carries a current of 1.0 A. Another circular loop of wire is concentric with (that is, has a common center with) the first and has a radius of 10
42. IE •• A circular loop of wire in the horizontal plane carries a counterclockwise current, as viewed from above. (a) Use the right-hand source rule to determine whether the direction of the
40. •• In Figure 19.32, find the magnetic field (magnitude and direction) at point A, located 9.0 cm away from wire 2 on a line perpendicular to the line joining the wires.
39. •• Two long, parallel wires separated by 0.20 m carry equal currents of 1.5 A in the same direction. Find the magnitude and direction of the magnetic field 0.15 m away from each wire on the
37. •• Two long, parallel wires carry currents of 8.0 and 2.0 A (▼ Figure 19.32). (a) What is the magnitude of the magnetic field midway between the wires?(b) Where on a line perpendicular to
36. • A solenoid is 0.20 m long and consists of 100 turns of wire. At its center, the solenoid produces a magnetic field of 1.5 mT. Find the current in the coil.
35. • In a physics lab, a student discovers that the magnitude of the magnetic field at a certain distance from a long wire is 4.0 μT. If the wire carries a current of 5.0 A, what is the distance
34. • A long, straight wire carries a current of 2.5 A. Find the magnitude of the magnetic field 25 cm from the wire.
33. • The magnetic field 7.5 cm directly above the center of a 25-turn coil of radius 15 cm is 0.80 mT. Find the current in the coil.
46. •• A set of jumper cables used to start a car from another car’s battery is connected to the terminals of both batteries. If 15 A of current exists in the cables at some instant during the
47. •• Two long, straight, parallel wires carry the same current in the same direction. (a) Use both the right-hand source and force rules to determine whether the forces between the wires are
8. Increasing only the coil area in an ac generator would result in (a) an increase in the frequency of rotation, (b) a decrease in the maximum induced emf,(c) an increase in the maximum induced emf,
7. The north end of a bar magnet is quickly pulled away from the center of a circular metallic loop. The magnet’s length is always perpendicular to the coil’s plane. As the south end of the
6. A bar magnet is thrust toward the center of a circular metallic loop. The magnet approaches with its length perpendicular to the coil’s plane. As the bar recedes from your view and approaches
5. Identical single loops A and B are oriented so they have the maximum amount of flux when placed in a magnetic field. Both loops maintain their orientation relative to the field, but in the same
4. Identical single loops A and B are oriented so they initially have the maximum amount of flux in a magnetic field. Loop A is then quickly rotated so that its normal is perpendicular to the
3. For a current to be induced in a wire loop, (a) there must be a large magnetic flux through the loop,(b) the loop’s plane must be parallel to the magnetic field, (c) the loop’s plane must be
2. The magnetic flux through a loop can change due to a change in which of the following (there may be more than one correct answer): (a) the area of the coil, (b) the strength of the magnetic
1. Which of the following is an SI unit of magnetic flux(there may be more than one correct answer): (a) Wb,(b) T·m2, (c) (T·m)/A, or (d) T?
52. ••• A crude classical (and wrong!) model for the production of the Earth’s magnetic field consists of a circular loop of current with a radius of 500 km with its center coincident with
51. •• (a) Exiting from a small linear accelerator near Washington, DC, a proton is moving parallel to the ground. What should the direction(s) of its velocity be in order to maximize the upward
50. ••• A circular wire (planar) coil consists of 100 turns and is wound around a very long iron cylinder of radius 2.5 cm and a relative permeability 2200. The loop carries a current of 7.5 A.
48. ••• Four wires running through the corners of a square with sides of lengtha, as shown in ▼ Figure 19.35, carry equal currents I. Calculate the magnetic field at the center of the square
32. • (a) Show that the right-hand side of Equation 19.13b gives the correct SI units for magnetic field. (b) Show that Equation 19.13b reduces to Equation 19.13a when the central axis location is
14. • In a velocity selector, a charged particle travels undeflected through perpendicular electric and magnetic fields whose magnitudes are 3000 N/C and 30 mT, respectively. Find the speed of the
11. ••• A beam of protons exits a particle accelerator due east at a speed of 3.0 × 105 m/s. They then enter a uniform magnetic field of magnitude 0.50 T that is oriented at 37° above the
10. •• (a) What angle(s) does a particle’s velocity have to make with the magnetic field direction for it to be subjected to half the maximum possible magnetic force, Fmax? (b) Express the
9. • An electron travels at a speed of 2.0 × 104 m/s through a uniform magnetic field of magnitude is 1.2 × 10−3 T.What is the magnitude of the magnetic force on the electron if its velocity
8. • An electron travels in the +x-direction in a magnetic field and is acted on by a magnetic force in the−y-direction. (a) In which of the following directions could the magnetic field be
7. •• A beam of protons is accelerated to a speed of 5.0 × 106 m/s in a particle accelerator and emerges horizontally into a uniform magnetic field. What magnetic field (direction and magnitude)
2. • Two identical bar magnets of negligible width are located in the x-y plane. Magnet #1 lies on the x-axis and its north end is at x = +1.0 cm, while its south end is at x = +5.0 cm. Magnet #2
30. • The magnetic field at the center of a 50-turn coil of radius 15 cm is 0.80 mT. Find the current in the coil.
29. ••• A rectangular wire loop with a cross-sectional area of 0.20 m2 carries a current of 0.25 A. The loop is free to rotate about an axis that is perpendicular to a uniform magnetic field of
27. •• A wire is bent as shown in ▶ Figure 19.31 and placed in a magnetic field with a magnitude of 1.0 T in the indicated direction. Find the net force on the whole wire if x = 50 cm and it
26. •• A horizontal dc power line carries a current of 1000 A east. If the Earth’s field at that location is northward with a magnitude of 5.0 × 10−5 T at 45° below the horizontal, what are
25. •• A wire carries a current of 10 A in the +x- direction.(a) Find the force per unit length on the wire if it is in a magnetic field that has components of Bx = 0.020 T, BY = 0.040 T, and Bz
24. •• A straight current-carrying wire 25 cm long is at right angles to a uniform horizontal magnetic field of 0.30 T in the −x-direction. (a) Along which of the x-y-z axes would the current
23. •• A wire carries a current of 10 A in the +x-direction in a uniform magnetic field of 0.40 T. Find the magnitude of the force per unit length and the direction of the force on the wire if
22. •• A horizontal magnetic field of 1.0 × 10−4 T is at 30° to the current in a straight, horizontal wire 75 cm long. If the wire carries a current of 15 A,(a) what is the magnitude of the
21. • A 2.0-m length of straight wire carries a current of 20 A in a uniform magnetic field of 50 mT at an angle of 37° from the direction of the current. Find the force on the wire.
20. • A straight, horizontal segment of wire carries a current in the +x-direction in a magnetic field that is directed in the −z-direction. (a) Is the magnetic force on the wire directed in the
18. ••• In a mass spectrometer, a beam of protons enters a magnetic field. Some protons make exactly a onequarter circular arc of radius 0.50 m. If the field is always perpendicular to the
23. Two identical appliances are on the same household circuit and the circuit breaker trips when someone tries to turn on both at the same time. Which of the following is true (there may be more
7. Resistors A and B are wired in parallel, and that combination is in turn connected in series to resistor C.The whole network is then connected across the terminals of a battery. Which of the
6. Two resistors (one of resistance 2.0 Ω and the other of 6.0 Ω) are connected in series to a battery. Which one produces the most joule heating: (a) the 2.0-Ω resistor,(b) the 6.0-Ω resistor;
5. Two resistors (one of resistance 2.0 Ω and the other of 6.0 Ω) are connected in parallel to a battery. Which one produces the most joule heating: (a) the 2.0-Ωresistor, (b) the 6.0-Ω resistor;
4. Resistors A and B are connected in parallel to a 12-V battery. A has 2.0 A of current and the total current in the battery is 3.0 A. Which has the most resistance:(a) A, (b) B, (c) both have the
3. Resistors A and B are connected in series to a 12-V battery. A has 9 V across it. Which has the least resistance: (a) A, (b) B, (c) both have the same, or(d) can’t tell from the data?
2. Which of the following must be the same for resistors in parallel: (a) voltage, (b) current, (c) power, or(d) energy?
1. Which of the following must be the same for resistors in series: (a) voltage, (b) current, (c) power, or (d) energy?
54. A computer hard drive that operates on 120 V is rated at 40 W when it is operating. (a) How much current does the drive draw? (b) What is the drive’s resistance?(c) How much energy (in kWh)
53. ••• (a) Find the individual monthly (30-day) electric energy costs (to the nearest dollar) for each of the following household appliances if the utility rate is$0.12/kWh: central air
50. •• An ohmic appliance is rated at 100 W when it is connected to a 120-V source. If the power company cuts the voltage by 5.0% to conserve energy, what is (a) the current in the appliance and
49. •• A student uses an immersion heater to heat 0.30 kg of water from 20 °C to 80 °C for tea. (a) If the heater is 75% efficient and takes 2.5 min to heat the water, what is its resistance?
8. For the circuit in Question 7, which of the following statements is true: (a) the voltage across C must be less than that across either A or B; (b) the voltage across C must be more than the
9. A multiloop circuit has just one battery. After leaving the battery, the current encounters a junction into two wires. One wire carries 1.5 A and the other 1.0 A.What is the current in the
22. The circuit breaker in a normal 120-V household circuit limits the total current in its circuit to (a) about 15–20 A,(b) about 1 A, (c) about 120 V, (d) about 100 A.
21. Which of the following enables an ammeter to make a correct measurement of current in a circuit element(there may be more than one correct answer):(a) connect the ammeter in series with the
20. To correctly measure the voltage across a circuit element, a voltmeter should be connected (a) in series with it, (b) in parallel with it, (c) between the high potential side of the element and
19. To accurately measure the current in a 1.0-kΩ resistor, an ammeter should have a resistance that is (a) much larger than 1.0 kΩ, (b) much smaller than 1.0 kΩ,(c) about the same as 1.0 kΩ, (d)
18. To accurately measure the voltage across a 1-kΩresistor, a voltmeter should have a resistance that is(a) much larger than 1 kΩ, (b) much smaller than 1 kΩ,(c) about the same as 1 kΩ, (d) as
17. An uncharged capacitor is charged by a battery through a resistor (situation #1). The capacitor is then recharged (using a different battery but the same resistor) to twice the final charge in
16. A charged capacitor discharges through a resistor(situation #1). The resistance is doubled and the identically charged capacitor allowed to discharge again(situation #2). How do the time
15. When a capacitor discharges through a resistor, the current in the circuit is a minimum (a) at the beginning of the process, (b) near the middle of the process,(c) at the end of the process, (d)
14. As a capacitor discharges through a resistor, the voltage across the resistor is a maximum (a) at the beginning of the process, (b) near the middle of the process,(c) at the end of the process,
13. A fully charged capacitor stores 2.5 mJ of electric energy. Then it has a resistor connected across its oppositely charged plates. What can you say about the total heat generated in the resistor
12. A multiloop circuit has just one battery with a terminal voltage of 12 V. After leaving the positive terminal of the battery, a wire takes you to a junction where the current(and circuit) splits
11. By our sign conventions, if a battery is traversed in the actual direction of the current in it, what can you say about the sign of the change in electric potential (the battery’s terminal
10. By our sign conventions, if a resistor is traversed in the direction opposite of the current in it, what can you say about the sign of the change in electric potential (the voltage) (a) it is
48. •• A 5.5-kW water heater operates at 240 V. (a) Should the heater circuit have a 20-A or a 30-A circuit breaker?(A circuit breaker is a safety device that “opens” the circuit – shutting
25. •• A copper wire has a 25-mΩ resistance at 20 °C.When the wire is carrying a current, heat produced by the current causes the temperature of the wire to increase by 27 °C. (a) What is the
24. •• (a) What is the percentage variation of the resistivity of copper over the temperature range from 20 °C to 100 °C? (b) Assume a copper wire’s resistance changes due to only resistivity
23. •• The wire in a heating element of an electric stove burner has a 0.75-m length and a 2.0 × 10−6 m2 crosssectional area. (a) If the wire is made of iron and operates at 380 °C, what is
17. • What terminal voltage must an ideal battery (no significant internal resistance) have to produce a 0.50-A current through a 2.0-Ω resistor?
16. • How much current is drawn from an ideal 12-V battery when a 15-Ω resistor is connected across its terminals?
15. • A battery labeled 12.0 V supplies 1.90 A to a 6.00-Ωresistor (Figure 17.16). (a) What is the terminal voltage of the battery? (b) What is its internal resistance?
26. •• When a resistor is connected to a 12-V source, it draws a 185-mA current. The same resistor connected to a 90-V source draws a 1.25-A current. (a) Is the resistor ohmic? Justify your
43. •• A 120-V air conditioner unit draws 15 A of current.If it operates for 20 min, (a) how much energy in kilowatt-hours does it require in that time? (b) If the cost of electricity is
42. •• A 200-W computer power supply is on 10 h per day.(a) If the cost of electricity is $0.15/kWh, what is the energy cost if this computer is used like this every day for a year (365 days)?
40. •• On average, an electric water heater operates for 2.0 h each day. (a) If the cost of electricity is $0.15/kWh, what is the cost of operating the heater during a 30-day month? (b) What is
38. •• An electric toy with a resistance of 2.50 Ω is operated by a 3.00-V battery. (a) What current does the toy draw? (b) Assuming that the battery delivers a steady current for its lifetime
37. IE •• An ohmic resistor in a circuit is designed to operate at 120 V. (a) If you connect the resistor to a 60-V power source, will the resistor dissipate heat at(1) 2, (2) 4, (3) 1/2, or (4)
28. •• (a) If the resistance of the wire in Exercise 27 cannot vary by more than ±5.0% from its value at 20°C, to what operating temperature range should it be restricted? (b) What would be the
12. ••• Car batteries are often rated in “ampere-hours” or A·h. (a) Show that the A·h has SI units of charge and specifically that 1 A·h = 3600 C. (b) A fully charged, heavy-duty battery
19. ••• For the circuit in ▼ Figure 18.29, find (a) the current in each resistor, (b) the voltage across each resistor, (c) the power delivered to each resistor, and(d) the total power
17. ••• Lightbulbs with the power ratings (in watts) given in ▼ Figure 18.28 are connected in a circuit as shown.(a) What current does the voltage source deliver to the circuit? (b) Find the

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