A person is unable to see objects nearer than 50 cm. He wants to read a book placed at a distance of 25 cm. Find the nature, focal length and power of the lens, he requires for his spectacles.

Explain with the help of diagram why the sun is visible to us two minutes before the actual sunrise and two minutes after the sunset.

What is “dispersion of white light” ? Draw a labelled diagram to illustrate the recombination of the spectrum of white light. Why it is essential that the two prisms used for the purpose should be identical and placed in an inverted position with respect to each other?

A student is unable to see clearly the words written on the blackboard placed at a distance of approximately 4 m from him. Name the defect of vision the boy is suffering from. Explain the method of correcting this defect Draw ray diagram for the:

i. defect of vision and also

ii. for its correction.

The near point of a hypermetropic eye is 1m. What is the nature and  power of the lens required to correct this defect ? Assume that the near point of the normal eye is 25 cm.