Exercise

A student holding a mirror in his hand, directed the reflecting surface of the mirror towards the Sun. He then directed the reflected light on to a sheet of paper held close to the mirror.

What should he do to burn the paper?

A student holding a mirror in his hand, directed the reflecting surface of the mirror towards the Sun. He then directed the reflected light on to a sheet of paper held close to the mirror.

Which type of mirror does he have?

A student holding a mirror in his hand, directed the reflecting surface of the mirror towards the Sun. He then directed the reflected light on to a sheet of paper held close to the mirror.

Will he be able to determine the approximate value of focal length of this mirror from this activity ? Give reason and draw ray diagram to justify your answer in this case.

The absolute refractive index of Ruby is $1.7$. Find the speed of light in Ruby. The speed of light in vacuum is $3\times {10}^8 \raisebox{1ex}{$\mathrm{m}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{s}$}\right.$.

State the laws of refraction of light. Explain the term 'absolute refractive index of a medium' and write an expression to relate it with the speed of light in vacuum.

Draw the path of a ray of light when it enters one of the faces of a glass slab at an angle of nearly $45°$. Label on it (i) angle of refraction, (ii) angle of emergence and (iii) lateral displacement.

What is meant by power of a lens? Write its SI unit. A student uses a lens of focal length $40 \mathrm{cm}$ and another of $-20 \mathrm{cm}$. Write the nature and power of each lens. 

A $10 \mathrm{cm}$ tall object is placed perpendicular to the principal axis of a convex lens of focal length $12 \mathrm{cm}$. The distance of the object from the lens is $18 \mathrm{cm}$. Find the nature, position and size of the image formed.