Current Electricity · Question 36

Find the equivalent resistance between two ends of the following circuit [figure]

1. r
2. r6
3. r3
4. r9

Answer

(4) r9

Solution

Mark the junctions P, N, Q and S:

[figure]

The upper wire joins P and Q ⇒ P and Q are the same point (left end).

The lower wire joins N and S ⇒ N and S are the same point (right end).

So the first resistor (P–N), the second (N–Q) and the third (Q–S) are all connected between the two ends ⇒ the three are in parallel.

1Req = 3r + 3r + 3r = 9r

Req = r9

Answer: (4)