Physics Review Question

Unit: Electricity and Magnetism Year: 1995 Question#: 28
Question: In the circuit diagram below, ammeter A measures the current supplied by the 10-volt battery. The current measured by ammeter A is

(1 ) 0.13 A
(2 ) 2.0 A
(3 ) 0.50 A
(4 ) 4.0 A


What is this question really asking?

Explanation by: Rachel M
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Answer 1
0.13 A

INCORRECT

In this problem, you must use a parallel circuit equation.
.13 would be the correct answer if it were a series circuit.
In a series,
R total= R1+R2 so... R total= 40+40= 80 V=IR 10A= I * 80 I= .13 A
but you must use this instead: 1/R total = 1/R1 + 1/R2
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Answer 2
2.0 A

INCORRECT

This can not be found using any of the circuit formulas correctly. If you got 2 A as your answer, you might have used R= VI, instead of V=IR, causing you to divide 20 by 10V, instead of 10V by 20. Remember to first use the parallel circuit formula :
1/R total= 1/R1 + 1/R2 and then plug the R into the equation above, V=IR return to top



























Answer 3
0.50 A

CORRECT

You should have done the following calculations: formulas: 1/R total= 1/R1 + 1/R2
V=IR
1/R total= 1/40 + 1/40 = 2/40 R = 40/2 = 20 10 volts= I * 20 I= 0.5 A
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Answer 4
4.0 A

INCORRECT

If you divided 40 by 10v, then you might have gotten 4A. But that is incorrect because you didn't take into account both resistors and the formulas were not used. Check out the correct answer (#3) to understand how to do this problem. You might also want to review the circuit equations. return to top


























What's this question really asking?

Do you know how to use the formulas for parallel circuit problems?

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