During open-heart surgery, a defibrillator can be used to bring a patient out of cardiac arrest. The resistance of the path is 500 Ω and a 10.0-mA current is needed.
(a) What voltage should be applied?
(b) If this voltage is applied for 0.010 s, how much charge moves through the torso of the patient?
(c) How many electrons pass through the wires connected to the patient?
Answer: (a) 5 V (b) 100 µC (c) 6.25 x 1014 electrons (Click and drag over the answer to highlight it)
3.2
Electron guns are used in X-ray tubes. The electrons are accelerated through a relatively large voltage and directed onto a metal target, producing X-rays.
(a) How many electrons per second strike the target if the current is 0.500 mA?
(b) What charge strikes the target in 0.750 s?
Answer: (a) 3.125 x 1015 electrons (b) 3.75 x 10-4 C
3.3
(a) Find the voltage drop in an extension cord having a 0.0600-Ω resistance and through which 5.00 A is flowing.
(b) A cheaper cord utilizes thinner wire and has a resistance of 0.300 Ω. What is the voltage drop in it when 5.00 A flows?
(c) Why is the voltage to whatever appliance is being used changed by this amount? What is the effect on the appliance?
Answer: (a) 0.3 V (b) 1.5 V
3.4
(a) What current flows through the bulb of a 3.00-V flashlight when its hot resistance is 3.60 Ω?
(b) Calculate the effective resistance of a pocket calculator that has a 1.35-V battery and through which 0.200 mA flows.
(c) What is the effective resistance of a car’s starter motor when 150 A flows through it as the car battery applies 11.0 V to the motor?
Answer: (a) 0.83 A (b) 6750 Ω (c) 0.073 Ω
3.5
(a) What is the resistance of a 20.0-m-long piece of 12-gauge copper wire having a 2.053-mm diameter?
(b) The diameter of 0-gauge copper wire is 8.252 mm. Find the resistance of a 1.00-km length of such wire used for power transmission.
Answer: (a) 104 mΩ (b) 320 mΩ
3.6
(a) To what temperature must you raise a copper wire, originally at 20.0ºC, to double its resistance, neglecting any changes in dimensions?
(b) Does this happen in household wiring under ordinary circumstances?
Answer: (a) 276°C
3.7
(a) Of what material is a wire made, if it is 25.0 m long with a 0.100 mm diameter and has a resistance of 77.7 Ω at 20.0ºC?
(b) What is its resistance at 150ºC?
Answer: (a) gold (b) 112 Ω
3.8
A charge of 4.00 C of charge passes through a pocket calculator’s solar cells in 4.00 h. What is the power output, given the calculator’s voltage output is 3.00 V?
Answer: 0.83 mW
3.9
A North American tourist takes his 25.0-W, 120-V (rms) AC razor to Europe, finds a special adapter, and plugs it into 240 V (rms) AC.
(a) What is the resistance of the razor?
(b) What current does the razor draw when plugged into a standard US outlet?
(c) Assuming constant resistance, what power does the razor consume as it is ruined? How much current does it draw?
Answer: (a) 576 Ω (b) 0.2 A (c) 100 W, 0.4 A
3.10
Two different electrical devices have the same power consumption, but one is meant to be operated on 120-V AC and the other on 240-V AC.
(a) What is the ratio of their resistances?
(b) What is the ratio of their currents?
(c) Assuming its resistance is unaffected, by what factor will the power increase if a 120-V AC device is connected to 240-V AC?
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