Question 10
The diagram shows a d.c.
circuit.
What is the resistance
between the points P and Q due to the resistance network?
A 0.47 Ω B 2.1 Ω C 3.0 Ω D 21 Ω
Reference: Past Exam Paper – June 2011 Paper 12 Q38
Solution:
Answer: C.
We need to simplify the
resistances.
Consider the two 6 Ω resistors in parallel. Let their
combined resistance be R1.
1 / R1 = 1/6 +
1/6
R1 = [1/6 +
1/6]-1 = 3 Ω
This 3 Ω combined
resistance is in series with the 3 Ω resistor in the lower branch.
Combined resistance in the
lower branch = 3 + 3 = 6 Ω
Equivalent resistance
between the points P and Q,
RT = [1/6 + 1/(3+3)]-1 = 3 Ω
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