The truth table of OR gate is

$$\matrix{ A & B & Y \cr 0 & 0 & 0 \cr 0 & 1 & 1 \cr 1 & 0 & 1 \cr 1 & 1 & 1 \cr } $$

It is seen that output of OR gate is Y = A + B.
If both or any one has 1 input then output will be 1.

A diode is said to be reverse biased if p-type semiconductor of p-n junction is at low potential with respect to n-type semiconductor of p-n junction. It is so for circuit (c).

In semiconductors at room temperature the electrons get enough energy so that they are able to over come the forbidden gap. Thus at room temperature the valence band is partially empty and conduction band is partially filled. Conduction band in semiconductor is completely empty only at 0 K.

V = $${{{V_0}} \over \pi }$$

$$ \Rightarrow $$ V = $$\left( {{{10} \over \pi }} \right)V$$