Resistors in series and parallel; power

Explanation of question 10

In Fig. 3.3, the p.d. between A and B will be

  1. 16.36V, A positive with respect to B
  2. 16.36V, B positive with respect to A
  3. 6V, A positive with respect to B
  4. 6V, B positive with respect to A

The answer is :- 4

24 V is applied across the two series 12 resistors, therefore, current through these resistors =

24
12+12

= 1 A

P.D. between A and negative terminal of battery = 1 x 12 = 12 V.

24 V is applied across the 3 and 9 resistors iin series,

so current through these resistors =

24
3+9

= 2 A.

P.D. between B and negative terminal of battery = 2 x 9 = 18 V.

A at a potential of 12 V and B at a potential of 18 V with respect to negative battery terminal gives a p.d. between A and B = 18 - 12 = 6 V, with B of greater potential than A.

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