The reverse biasing in a $PN$ junction diode

For the diagram shown,the resistances between points $A$ and $B$ when the ideal diode $D$ is forward biased is $R_1$ and when it is reverse biased is $R_2$. The ratio $R_1: R_2$ is

When a silicon $PN$ junction is in forward biased condition with a series resistance,it has a knee voltage of $0.6\, V$. The current flowing through it is $5\, mA$ when the $PN$ junction is connected to a $2.6\, V$ battery. The value of the series resistance is.....$\Omega$.

Currents flowing in each of the following circuits $A$ and $B$ respectively are

In the figure shown, if the diode forward voltage drop is $0.2 \, V$, the voltage difference between $A$ and $B$ is (in $V$)

$A$ potential barrier of $0.4 \,V$ exists across a p-n junction. An electron enters the junction from the $n$-side with a speed of $6.0 \times 10^{5} \,ms^{-1}$. The speed with which the electron enters the $p$-side will be $\frac{x}{3} \times 10^{5} \,ms^{-1}$. The value of $x$ is ..............
(Given: mass of electron $= 9 \times 10^{-31} \,kg$,charge on electron $= 1.6 \times 10^{-19} \,C$.)