An $LED$ is constructed from a $pn$ junction based on a certain semiconducting material whose energy gap is $1.9 \ eV$. The wavelength of the emitted light is:

Why is the $I-V$ characteristic of a solar cell drawn in the fourth quadrant of the coordinate system?

Which semiconductor device converts electrical energy into light?

The material used in the fabrication of infrared $LED$'s is

Assertion $(A)$: $Si$ and $GaAs$ are the preferred materials for solar cells.
Reason $(R)$: Both these materials have energy band gaps much below the energy level corresponding to the maximum solar irradiance in the solar spectrum.

Consider the following statements $:$
$A.$ The junction area of a solar cell is made very large compared to a photodiode.
$B.$ Solar cells are not connected with any external bias.
$C.$ $\text{LED}$ is made of heavily doped $p-n$ junction.
$D.$ Increase of forward current results in continuous increase of $\text{LED}$ light intensity up to a saturation point.
$E.$ $\text{LED}$ must be connected in forward bias for the emission of light.
Which of the following statements are correct?