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
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What's this question really asking?
Do you know how to use the formulas for parallel circuit problems?
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