466 Chapter 21 Electric Current Two bulbs have ratings of 60 watts and 120 watts

Question

466 Chapter 21 Electric Current Two bulbs have ratings of 60 watts and 120 watts. Which 62. Two bullbs have ratings of bulb carries the higher current? Explain. 62. Two bualbs have ratings of 60 watts and 1230 watts. Which 61. bulb has the higher resistance? Explain. Exercises 63. What is the resistance of a lightbulb that draws 0.5 A 64. You plug a vacuum cleaner into a 120-V outlet with A 3 resistor is connected in parallel with a 12n resistor, and the combination is connected to a 12-V battery. How much current does the battery sup 74. when it is plugged into a 120-V outlet? nothing else on the circuit. If the 15-A circuit breaker is 75. A heating element is rated at 1400 tripped, what is the maximum possible resistance of the vacuum's motor? A heating element is rated at 1400 W. How much current does it draw when it is connected to a 120-V li is 75. What is the power used by a toaster that draws a current of 8 A when connected to a 120-V line? 76. 65. The coils of a heater have a resistance of 10 when hot What current does the heater draw when plugged into a 77. A DVD player has a masimum power rating of 24 W when 120-V outlet? plugged into a 120-V outlet. What is the maximum cur rent that it requires? If a clock draws a maximum current of 5 mA from a l V line, what is its maximum power consumptios A + resistor is connected to a 12-V battery, what is the current through the battery? What is the power dissipated 66. You plug your new 9-02 hair dryer into a 120-V outlet and trip the 10-A circuit breaker. If you plug the hair dryer 7s. Ifa clock draws a maximum current of 5 mA 78. into a line with a 15-A breaker, will i trip the breaker? Assume that nothing else is plugged into either circuit. 79, If a lightbulb has a resistance of 8 and a current of 0.5 A, at what voltage is it operating? 67. by the resistor? A 3- resistor draws a current of 2 A when hooked up to a battery of unknown voltage. What is the battery's vo age? What is the power dissipated by the resistor? What is the power rating of a heating coil with a resis- tance of 12 that draws a current of 20 A? A coffeemaker has a resistance of 12 and draws a cur- rent of 10 A. What power does it use? 68. 80. 69. Two 1V batteries are connected in series to a 302 resis- 70. Two IA, batteries are connected in parallel to a 341 resis- 71. Tw3- resistors are connected in series to a 12-V bat- required for the bulb to draw a current of 0.5 A tor. How much current flows through each battery? tor. How much current flows through each battery? tery. What single resistor, if connected to the battery 81. 82, alone (called the equivaleut esistance), would draw this same current? What is the current through the battery? circuit? 84. What is the resistance of the coil in a 1500-W heater? 72. A 2-12 and a 4-02 resistor are connected in series to a 12V battery. What is the current through each resistor? Use Ohm's law to show that the voltage drops across the indi- vidual resistors add up to 12 V 85. If a hair dryer is rated at 1200 W, how much energy is 86. If a 60-W bulb is left on continuously in a secluded hall- 87. used to operate the hair dryer for 8 min? way, how much energy is used each month? 73. Two 442 resistors are connected in parallel to a 12V bat- tery. Use the fact that the voltage across each of the resis- tors is 12 V to find the total current through the battery What single resistor, if connected to the battery alone (called the equivalernt wesistance), would draw this same current If electricity costs 15c/kWh, how much does it cost to burn a 100-W bulb for one day? A 1500-W heater for a sauna requires 40 min to heat the sauna to 190"'F. What does this cost if electricity sells fos 12c/kWh? 88. 8. A 1:0W heater for

Explanation / Answer

64. as the circuit breaker is tripped, that means the maximum current was flowing through the circuit
i = 15 A
V = 120 V
V = iR
R = 120/15 = 8 ohms
68. given R = 250 ohm
i = 0.5 A
Using ohms law
V = iR
V = 250*0.5 = 125 V
71. two series resistors can be replaced by a single equivalent resistor which is equal to algebraic sum of tyhe original two resistors
so, Reff = R1 + R2 = 6 ohm
76. i = 8A
V = 120 V
power = Vi
P = Vi = 120*8 = 960 W
82. R = 12 ohm
i = 10 A
power, P = Vi
but V = iR
so, P = i^2*R = 100*12 = 1200 W

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