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# Germanium and silicon junction diodes are connected in parallel. These are connected in series with a resistance $\mathrm{R}$, a milliammeter $(\mathrm{mA})$ and a key $(\mathrm{K})$ as shown in Fig. When key $(\mathbf{K})$ is closed a current begins to flow in the milliammeter. The potential drop across the germanium diode is then(A) 0.3 V(B) 0.7 V(C) 1.1 V(D) 12 V

Last updated date: 12th Aug 2024
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Hint: We know that diode (PN junction) in an electrical circuit allows current to flow more easily in one direction than another. Forward biasing means putting a voltage across a diode that allows current to flow easily, while reverse biasing means putting a voltage across a diode in the opposite direction. The Forward bias decreases the resistance of the diode whereas the reversed bias increases the resistance of the diode. In forward biasing the current is easily flowing through the circuit whereas reverse bias does not allow the current to flow through it.

The germanium diode is reverse biased and the silicon diode is forward biased. Therefore, there will be no current in the branch of germanium diode. The potential barrier of silicon diode is $0.7 \mathrm{V}$. Therefore, for conduction minimum potential difference across silicon is $0.7 \mathrm{V}$.
Maximum potential difference across resistance, $\mathrm{R}=12-0.7=$$11.3 \mathrm{V}$