Exercise

When light rays pass through a lens, they bend and change their direction. This is called _____ of light.

The degree of convergence or divergence of light rays achieved by a lens is expressed in terms of its power. The power, $\mathrm{P}$ of a lens is given by the relation,
$\mathrm{P}=\frac{1}{\mathrm{f}}$
where, $f$ is the focal length of the lens in metres.
Many optical instruments use a number of lenses. These lenses are combined to increase the magnification and sharpness of the images produced. The resultant or net power of the combination of lenses placed in contact with each other is given by the algebraic sum of the individual powers of each of the lenses. If the individual powers of two lenses are ${\mathrm{P}}_1$ and ${\mathrm{P}}_2$, the resultant power, $\mathrm{P}$ is given by
$\mathrm{P}={\mathrm{P}}_1+{\mathrm{P}}_2$
The focal length, $f$ of the combination of two lenses of focal lengths $f_1$ and $f_2$ is given by
$f=\frac{f_1{f}_2}{f_1+f_2}$
Suppose you are given three lenses $- \mathrm{A}, \mathrm{B}$ and $\mathrm{C}$ with focal lengths $10 \mathrm{cm}, 20 \mathrm{cm}$ and $30 \mathrm{cm}$. $\mathrm{A}$ and $\mathrm{B}$ are convex lenses whereas $\mathrm{C}$ is a concave lens. The three lenses are kept in contact with each other.
On the basis of the above information and what you have studied in the course, answer the following question:

The power of the combination of lenses is

Describe an experiment to show the apparent depth of a coin at the bottom of a vessel due to refraction through water filled in the vessel. Provide necessary diagrams.

A ray of light travelling from glass to air will bend towards the normal after refraction.

Angle of incidence is always equal to the angle of _____.

When light travels from a rarer to a denser medium, it _____

Normal incidence means angle of incidence is zero.

_____ (concave/convex/plane) mirrors are used as rear-view mirrors in automobiles.