NCERT Solution for Class 10 Science Chapter 12

Electricity

NCERT Books for Session 2020-2021

CBSE Board and UP Board

Exercises Questions

Page No-221

Questions No-11

# Show how you would connect three resistors, each of resistance 6 W, so that the combination has a resistance of (i) 9 ohm, (ii) 4 ohm.

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If we connect the resistors in series, then the equivalent resistance will be the sum of the resistors, i.e., 6 Ω + 6 Ω + 6 Ω = 18 Ω, which is not desired. If we connect the resistors in parallel, then the equivalent resistance will be

6/2= 3ohm

which is also not desired. Hence, we should either connect the two resistors in series or parallel.

(i) Two resistors in parallel

Two 6 Ω resistors are connected in parallel. Their equivalent resistance will be

1/(1/6 + 1/6) = 3ohm

The third 6 Ω resistor is in series with 3 Ω. Hence, the equivalent resistance of the circuit is 6 Ω + 3 Ω = 9 Ω.

(ii) Two resistors in series

Two 6 Ω resistors are in series. Their equivalent resistance will be the sum 6 + 6 = 12 Ω

The third 6 Ω resistor is in parallel with 12 Ω. Hence, equivalent resistance will be

1/(1/12 + 1/6) = 4ohm

Therefore, the total resistance is 4 Ω.