question_answer

The diode used in the circuit shown in the figure has a constant voltage drop of 0.5 V at all currents and a maximum power rating of 100 mill watt. What should be the value of the resistor R, connected in series with the diode, for obtaining maximum current?

A)  200\[\Omega \]                              

B)  6.67 \[\Omega \]

C)  5\[\Omega \]                                   

D)  1.5\[\Omega \]

Correct Answer: C

Solution :

                Key Idea: The  value of resistance can be calculated by the Ohms law \[\left( R=\frac{V}{I} \right)\]. Current in circuit \[I=\frac{P}{V}=\frac{100\times {{10}^{-3}}}{0.5}\]                                 \[=200\times {{10}^{-3}}A\] Voltage across resistance R,                 \[V=1.5-0.5=1.0V\] Thus, Resistance \[R=\frac{V}{I}=\frac{1}{200\times {{10}^{-3}}}=5\Omega \]                 NOTE : In the circuit given,   the   positive     terminal of the cell is connected to p-side and negative terminal  is connected to n-side of unction diode. So, it is forward biased.