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Question
Find the current through the resistance R in figure if (a) R = 12Ω (b) R = 48Ω.
(Assume that the resistance of each diode is zero in forward bias and is infinity in reverse bias.)
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Solution
(a) When R = 12 Ω:
The 4 V battery is forward biassing the diode and the 6 V battery is reverse biassing the diode, so the diode is effectively reverse biassed. It acts like an open circuit so that no current flows through this branch. Hence, to simplify the circuit, this branch can be removed.
The current through R on applying the KVL in the circuit is given by
\[i = \frac{10}{24} = 0 . 4166 = 0 . 42 \]A
(b) Similarly, for R = 48 Ω,
\[i = \frac{10}{48 + 12} = \frac{10}{60} = 0 . 16 \] A
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