The voltage across a diode in a full wave rectifier having input voltage of peak value Vm during its non conducting period is0−Vm−2 Vm−4 Vm

The voltage across a diode in a full wave rectifier during its non-conducting period is -Vm.

Here's why:

In a full wave rectifier, two diodes are used. During the positive half cycle of the input, one diode is forward biased (conducting) and the other is reverse biased (non-conducting). During the negative half cycle, the roles are reversed.

When a diode is non-conducting (reverse biased), it's as if it's an open switch - no current flows through it. The voltage across an open switch is equal to the supply voltage. In this case, the supply voltage is the input voltage to the rectifier.

During the non-conducting period, the input voltage is negative (since we're in the negative half cycle). So, the voltage across the non-conducting diode is -Vm.