Unit: Electricity and Magnetism
Year: 1994 Question#: 30
Question: Which two of the resistor arrangements shown in the diagram have equivalent resistance?
A) |
C) |
B) |
D) |
(1
) A and B
(2
) B and C
(3
) C and D
(4
) D and A
What is this question really asking?
Explanation by: Kristina A
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Answer 1
A and B
INCORRECT
I don't know how you got this. Maybe you did: 1/1 =1 and 8/8 = 1 but in that case
you would get all the answers correct. If you chose this answer you obviously have
a lack of knowledge in this subject. Remember, series resistance adds, parallel
resistance doesn't
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Answer 2
B and C
CORRECT
You must have used the series and parallel circuit formulas:
B) 1/Rt = 1/R1 + 1/R C) Rt = R1 + R2
1/Rt= 1/8
+1/8 = 2
+ 2
1/Rt= 1/4
= 4
Rt = 4 
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Answer 3
C and D
INCORRECT
Both resistors are 2 Ohms on both circuits but one is parallel and other is series.
You need to use different formulas.
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Answer 4
D and A
INCORRECT
Maybe you thought the current goes through one resistors in the parallel and both
in the series. But you cna't thing of it this way. Check out the formulas.
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What's this question really asking?
You need to know what series and parallell circuits look like then affectively use
the formulas to determine the resistance.
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