In the following circuit,the equivalent resistance between $A$ and $B$ is ..... $\Omega$.

$A$ $P-N$ junction diode is in forward bias with a current of $10 \ mA$. The potential drop across the diode is $0.5 \ V$. Assuming the current is independent of the potential,what is the maximum voltage of the battery in series with a $200 \ \Omega$ resistor to maintain this forward bias condition? (in $V$)

Two identical $p-n$ junctions are connected in series with a battery in three ways,as shown below. The potential drops across the two $p-n$ junctions are equal in:

Different voltages are applied across a $P-N$ junction and the currents are measured for each value. Which of the following graphs is obtained between voltage and current?

If no external voltage is applied across a $P-N$ junction,there would be:

If the forward voltage in a diode is increased,the width of the depletion region $\qquad$ .