Physics Review Question

Unit: Electricity and Magnetism
Year: 1994 Question#: 31
Question: A clothes dryer connected to a 240-volt line draws 30. amperes of current for 20. minutes (1200 seconds). Approximately how much electrical energy is consumed by the dryer.

(1 ) 4.8 * 103 J
(2 ) 7.2 * 103 J
(3 ) 1.4 * 105 J
(4 ) 8.6 * 106 J

What is this question really asking?




Explanation by: Ajemo H

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Answer 1
4.8 * 103 J

INCORRECT

The equation for energy is W=VIt. Where W=energy, V=voltage, I=current, and t=time.

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Answer 2
7.2 * 103 J

INCORRECT

The equation for energy is W=VIt. Where W=energy, V=voltage, I=current, and t=time. return to top



























Answer 3
1.4 * 105 J

INCORRECT

The equation for current is W=VIt. Where W=energy, V=voltage, I=current, and t=time. return to top


























Answer 4
8.6 * 106 J

CORRECT

The equation for energy is W=VIt. Where W=energy, V=voltage, I=current, and t=time. If you plug 240-volt in for voltage, 30. A in for current, and 1200 seconds in for time. you can solve for W (electricle energy). the number you get is 8640000 J. since all of the answers have at least two significant figures, this number is rounded to 8600000 J. Then to put it in scientific notation, you take the last two digits and turn them into a number less then ten. so instead of 86, it would be 8.6. Then you count the number of places. You had to move the decimal notation to make the number less than ten. This numbe is the power to which you will put ten to in the notation. In this problem that number is 6. the whole thing ends up being 8.6 * 106 J. return to top


























What's this question really asking?

This question is asking if you know how to use the formulas you are given for the test in the appropriate places. It also asks if you know your sientific notation. return to top

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