$A$ photodiode is a device

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

Explain the design,working,uses,and benefits of a light-emitting diode $(LED)$.

$A$ family uses $8 \; kW$ of power.
$(a)$ Direct solar energy is incident on the horizontal surface at an average rate of $200 \; W$ per square meter. If $20 \%$ of this energy can be converted to useful electrical energy, how large an area is needed to supply $8 \; kW$?
$(b)$ Compare this area to that of the roof of a typical house.

Consider the following statements $A$ and $B$ and identify the correct answer:
$A$. For a solar-cell,the $I-V$ characteristics lies in the $IV$ quadrant of the given graph.
$B$. In a reverse biased $pn$ junction diode,the current measured in $(\mu A)$ is due to majority charge carriers.

For the emission of light,a light emitting diode $(LED)$ is: