MCQ
The relation between the linear magnification $m,$ the object distance $u$ and the focal length $f$ is
- A$m = \frac{{f - u}}{f}$
- ✓$m = \frac{f}{{f - u}}$
- C$m = \frac{{f + u}}{f}$
- D$m = \frac{f}{{f + u}}$
✓
Answer
Correct option: B.
$m = \frac{f}{{f - u}}$
b
(b) $m = - \frac{v}{u}$ also $\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$
(b) $m = - \frac{v}{u}$ also $\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$
==> $\frac{u}{f} = \frac{u}{v} + 1$
==> $ - \frac{u}{v} = 1 - \frac{u}{f}$
$ \Rightarrow \frac{{ - v}}{u} = \frac{f}{{f - u}}$ so $m = \frac{f}{{f - u}}$.
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