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 milliwatts. What should be the value of the resistor R, connected in series with the diode, for obtaining maximum current?

5 Ω

Maximum current in the circuit

I = P/V

$∴I=\frac{100×10^{-3}}{0.5}=0.2\,amp.$

Now, $R=\frac{voltage\,drop\, across\, resistance}{0.5}=\frac{1}{0.2}=5Ω$