The built-in potential of a $p-n$ junction diode is $0.7 \,V$. If the diode is forward biased and the applied voltage is $0.3 \,V$, the effective barrier height is (in $\,V$)

$D_1$ and $D_2$ are two ideal diodes. Find the values of $i_1$ and $i_2$.

If the $p-n$ junction diode is unbiased,

Refer to the circuit diagram given in the figure. Which of the following observations are correct?
$A.$ Total resistance of the circuit is $6 \ \Omega$.
$B.$ Current in the ammeter is $1 \ A$.
$C.$ Potential across $AB$ is $4 \ V$.
$D.$ Potential across $CD$ is $4 \ V$.
$E.$ Total resistance of the circuit is $8 \ \Omega$.
Choose the correct answer from the options given below:

When a semiconducting device is connected in series with a battery and a resistance,a current is found to flow in the circuit. If,however,the polarity of the battery is reversed,practically no current flows in the circuit. The device may be

The diode voltage is $0.5 \ V$ and the maximum power rating is $100 \ mW$. To obtain the maximum current in the circuit,the value of $R$ should be .......... $\Omega$.