$A$ $p-n$ photodiode is fabricated from a semiconductor with a band gap of $2.5 \, eV$. It can detect a signal of wavelength:

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 $\Omega$.

Assertion: $A$ $P-N$ junction diode is used in reverse bias to detect the intensity of light.
Reason: In reverse bias condition,current is small but it is more sensitive to changes in intensity of incident light.

Photodiodes are mostly operated in reverse biased condition because

The schematic symbol of a light emitting diode $(LED)$ is:

Which wavelength of the Sun is primarily used to generate electric energy in solar cells?