A diode conducts current only when the potential of point A is higher than the potential of point B, otherwise it doesn't allow the current to pass. When it conducts, the voltage drop across an ideal diode is zero.
Consider a circuit with an ideal diode as shown below. The input voltage Vin is shown on the left.
[Figure: Shows circuit diagram with diode and voltage waveforms]
What is the output voltage Vout?
a) a
b) b
c) c
d) d