Class 12 NEET Physics Semiconductor Electronics Part 2

Concept:A diode behaves as a closed switch when forward biased and as an open switch when reverse biased.Circuit:The source $v_i$, the diode $D$ and the resistor $R$ form a single series loop, so the same current flows through all of them.The diode is connected with its anode towards the source, so it conducts when $v_i > 0$ and blocks when $v_i < 0$.Step 1 (positive half-cycle, $v_i > 0$):The diode is forward biased and conducts, so for an ideal diode the voltage across it is $v_D \approx 0$.The full input then appears across $R$.Step 2 (negative half-cycle, $v_i < 0$):The diode is reverse biased and blocks the current.With no current, the drop across $R$ is zero, so the entire source voltage appears across the diode, $v_D = v_i$, which is negative.Step 3 (resulting waveform):The voltage across $D$ is zero throughout the positive half-cycle and follows the full sinusoidal swing of $v_i$ (a negative hump) throughout the negative half-cycle.Key point:The voltage across $R$ is the positive half-wave, while the voltage across $D$ is the complementary part, i.e. flat zero in the positive half and the negative half-wave in the negative half.Answer:The correct option is the waveform that shows $v_D = 0$ for the positive half-cycle and the full negative sinusoidal swing for the negative half-cycle.