Ohm's law fails in

When the $P$ end of a $P-N$ junction is connected to the negative terminal of the battery and the $N$ end to the positive terminal of the battery,then the $P-N$ junction behaves like:

As per the given circuit, the value of current through the battery will be $\dots \; A$.

In the circuit shown,if the forward voltage drop for the diode is $0.5\, V$,the current in the circuit will be.....$mA$.

To make a $PN$ junction conducting,what condition must be met?

An electron in the $n$-region of a $p-n$ junction moves towards the junction with a speed of $5 \times 10^5 \ m/s$. If the barrier potential of the junction is $0.45 \ V$, then the speed with which the electron enters the $p$-region after penetration through the barrier is (Charge of the electron $e = 1.6 \times 10^{-19} \ C$ and mass of the electron $m = 9 \times 10^{-31} \ kg$).