EXERCISE 16

The magnifying power of a simple microscope is given by$1+\raisebox{1ex}{$D$}\!\left/ \!\raisebox{-1ex}{$f$}\right.$ where $D$ is the least distance of distinct vision. For a long-sighted person $D$ is greater than the usual. Does it mean that the magnifying power of a simple microscope is greater for a long-sighted person as compared to a normal person?

Street lamp-posts appear to be shorter the farther they are away, although all are of same height. Why does it happen so?

When the lights of a brightly lit room are suddenly put out, the people of the room are blinded for a moment. Why?

A person wears bifocal converging spectacles, one surface of each lens being spherical and the other cylindrical. State the defects in his vision and explain how the spectacles correct them.

A compound microscope consists of an objective lens of focal length $2 \mathrm{cm}$ and an eye-piece lens of a focal length $6.25 \mathrm{cm}$ separated by a distance of $15 \mathrm{cm}$. How far from the objective should an object be placed in order to obtain the final image at the least distance of distinct vision $(25 \mathrm{cm})$.

A compound microscope consists of an objective lens of focal length $2.0 \mathrm{c}\mathrm{m}$ and an eyepiece of focal length $6.25 \mathrm{c}\mathrm{m}$ separated by a distance of $15 \mathrm{c}\mathrm{m}$. How far from the objective should an object be placed in order to obtain the final image at infinity.

On the 50th birthday, a person can see distinctly object at a distance $25 \mathrm{cm}$ with $+2.5D$ glasses. Ten years later, he reads a letter with the same glasses, but he has to keep the letter $50 \mathrm{cm}$ away. What power of lens should he now use?

A short-sighted person cannot see objects more than 25 $\mathrm{cm}$ away. If the distance between his spectacle and the eye-lens be $1 \mathrm{~cm}$, what power does he need to see far away objects?