Q. Figure represents a load consisting of three identical resistances connected to an electric energy source of emf 12 V and internal resistance 0.6 Ω . The ammeter reads 2A. The magnitude of each resistance is

(a) 3.6Ω

(b) 7.2Ω

(c) 16.2Ω

(d) 10.8Ω

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Ans: (c)

Sol: let R be the magnitude of each external resistance .

As all the external resistances are in parallel , therefore net external resistance

$\displaystyle R_P = \frac{R}{3} $

Current , $\displaystyle I = \frac{E}{\frac{R}{3} + r} $

$\displaystyle 2 = \frac{12}{\frac{R}{3} + 0.6} $

$\displaystyle 2 = \frac{12 \times 3}{R + 1.8} $

2R + 3.6 = 36

2R = 32.4

R = 16.2 Ω