Most household power in North America is 120 V alternating current (VAC). Howeve

Question

Most household power in North America is 120 V alternating current (VAC). However, some high-power appliances such as electric ranges and clothes dryers typically require a special 220 V circuit. In this problem, you will calculate the energy, power, and current required by a dryer. You will also compare different methods of storing the energy required to run this appliance in a typical drying cycle. Consider a dryer that operates on 220 V electricity, and it consumes an average power of 3200 IV. For this homework, the "Alternating Current" part of the story is irrelevant, so please use our ordinary DC equations (Perhaps this dryer has been specially made for physics experiments so it has a second input that allows it to operate on DC voltage as well!) For each problem, show your algebra and your answer with units Most of the power consumed by the dryer goes into producing heat. Dryers have a "heating element" which is a long coil of wire and can be treated as a single resistor. Using the value of power, and the operating voltage, calculate this resistance. What is the average current drawn by the dryer? A USB port can be used as a 5 V, 500 mA DC power supply. How many USB ports would it take to produce 3200 W?

Explanation / Answer

1.

Voltage = V = 220 volts

Power , P = 3200 Watt

Resistance , R

Using the formula

P = V2/R

3200 = 2202/R

R = 151.25 ohm

2.

Using ohm's law

V = i R

i = V/R = 220/151.25 = 1.45 A

3.

Power of a USB port , P = Vi = 5 x 0.5 = 2.5 Watt

Total Power = 3200 Watt

n = number of USB ports = Total power / P = 3200 / 2.5 = 1280

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