What is meant by coherent sources of light? 

A ray of light is incident on a transparent medium at polarising angle. What is the angle between the reflected ray and the refracted ray? 

Name the physical principle on which the working of optical fibres is based? 

What is meant by short-sightedness?

How does the focal length of a convex lens change with increase in wavelength of the incident light? 

With reference to the photoelectric effect, what is meant by the threshold wavelength? 

Half life of a certain radioactive element is 3.465 days. Find its disintegration constant. 

Binding energy per nucleon for helium nucleus  is 7.0 MeV. Find the value of mass defect for helium nucleus. 

19.

Write one balanced reaction representing nuclear fusion?

Draw the truth table of a NOR gate.