What is a wavefront? Describe different types of wavefront

. A compound microscope has a magnifying power of `$100$` when the image is formed at infinity. The objective has focal length $0.5 \mathrm{cm}$ and the tube length is $6.5 cm$  What is  the focal length of the eye-piece

Draw circuit diagram for a $\mathrm{P}-\mathrm{N}$ junction to obtain reverse bias characteristic curves. Explain the phenomenon of reverse breakdown for a $\mathrm{P}-\mathrm{N}$ junction in reverse bias state by following process-

$\left(\mathrm{ii}\right)$ Zener breakdown

LED is a p-n junction diode which is ?