(a) How are infrared waves produced? Why are these waves referred to as heat waves? Give any two uses of infrared waves.

OR

(b) How are X-rays produced? Give any two uses of these.

In the given figure the radius of curvature of curved face in the plano-convex and the plano-concave lens is $$15 \mathrm{~cm}$$ each. The refractive index of the material of the lenses is 1.5. Find the final position of the image formed.

What happens to the interference pattern when two coherent sources are

(a) infinitely close, and

(b) far apart from each other

(a) What is meant by ionisation energy? Write its value for hydrogen atom.

OR

(b) Define the term, mass defect. How is it related to stability of the nucleus?