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?

How does the height of the potential barrier change in forward bias and reverse bias?

$A$ diode having a potential difference of $0.5\, V$ across its junction,which does not depend on the current,is connected in series with a resistance of $20\, \Omega$ across a source. If $0.1\, A$ passes through the resistance,then what is the voltage of the source (in $, V$)?

The circuit shown in the figure contains two diodes,each with a forward resistance of $30 \, \Omega$ and infinite backward resistance. If the battery is $3 \, V$,the current through the $50 \, \Omega$ resistance (in ampere) is

In the given options,the diode that is forward biased is

Find the current $i$ in the circuit shown.