In a photodiode,the value of the $emf$ produced by a monochromatic light beam is directly proportional to

In optical fiber communication, an $APD$ semiconductor is used for:

The figure shows $2$ $LEDs$ that can be used as a polarity detector. Applying a positive source voltage results in a green light,while negative supplies result in a red light. Packages of such combinations are commercially available. Find the resistor $R$ to ensure a current of $20 \ mA$ through the $ON$ diode for the configuration. Both diodes have a reverse breakdown voltage of $3 \ V$ and an average turn-on voltage of $2 \ V$. The source voltage is $8 \ V$. Find $R$ in $\Omega$.

In a $PN$ junction photocell,the value of the photo-electromotive force produced by monochromatic light is proportional to

The $I-V$ characteristics for a junction diode are shown. The device is

The $I-V$ characteristic of an $LED$ is represented by which of the following graphs?