Question

The graphs given apply to a convex lens of focal length f, producing a real image at a distance v from the optical centre when self luminous object is at distance u from the optical centre. The magnitude of magnification is m. Identify the following graphs with the first named quantity being plotted along y-axis. Assume object distance greater than focal length

Answer 1

Given:- A convex lens of focal length f & image is real magnification m.

$\left|u\right|>$ f.

(a) v against u.

for a convex lens when an object moves from infinity towards lens then image will moves from focus towards infinity hence.

$u=f\nu =\infty \&u=\infty \nu =f$

which is in curve 2.

(B) From A

when $\frac{1}{u}=\frac{1}{f}\frac{1}{\nu }=0$

& when $\frac{1}{u}=\frac{1}{\infty }=0\frac{1}{\nu }=\frac{1}{f}$

Hence when $\frac{1}{u}$ increases

$\frac{1}{\nu }$ decreases.which is shown in curve/graph 3 & it will be a straight line as

$\frac{1}{\nu }-\frac{1}{u}=\frac{1}{f}$.

(c) m against v .

In this case $m=\frac{v}{u}$

Hence $m\alpha v$ which means it will be straight line with positive slope.