What is meant by Fraunhofer lines?

What is Fraunhofer lines?

(a) (i) What is meant by diffraction of light? (ii) In Fraunhofer diffraction, what kind of source of light is used and where is it situated ? (b) Obtain the relation, d sin theta= lambda for the first minima of the diffraction pattern of a single slit of width d using light of wavelength lambda .

What is meant by electric lines of force represent ? Explain repulsion between two like charges on their basis.

Explain what is meant by an electric line of force? Give its two important properties ?

Fraunhofer lines are due to