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