What is $p$-$n$ junction diode? Draw a diagram of forward and reverse biasing and explain how thickness of depletion region changes.

What is meant by rectifier and rectification? Draw circuit diagram of a $p$-$n$ junction diode as full and half-wave rectifier.

What do you understand by light-emitting diode (LED)? Explain photodiode and distinguish LED and photodiode. Draw their biasing also.

A $p$-$n$ junction diode can withstand currents up to a maximum of $10 \mathrm{mA}$. A resistor $R=200 \mathrm{\Omega }$ is connected in series with it. The diode, when forward-biased, has a potential drop of $0.5 \mathrm{V}$ across it which is assumed to be independent of current. Find the maximum voltage of the battery used to forward bias the diode.

When the voltage drop across a $p$-$n$ junction diode is increased from $0.65 \mathrm{V}$ to $0.70 \mathrm{V}$, the change in the diode current is $5 \mathrm{mA}$. What is the dynamic resistance of the diode?

A $p$-$n$ junction diode is connected to a series resistor of $100 \mathrm{\Omega }$ and a $4.5 \mathrm{V}$ DC battery The barrier potential at the junction is $0.5 \mathrm{V}$. Find the current in the circuit.