A 2 cm high object is placed at a distance of 20 cm from a concave mirror. A real image is formed 40 cm from the mirror. Calculate the focal length of the mirror and the size of the image. [3 MARKS]

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Solution

Problem: 3 Marks

Given:
$u = - 20 c m$

$v = - 40 c m$

We know Mirror formula
$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$

$\frac{1}{f} = \frac{1}{- 20} + \frac{1}{- 40}$

$f = - 13.3 c m$

Focal length of the mirror is 13.3 cm

We know
$\frac{h_{i}}{h_{o}} = \frac{- v}{u}$

$\frac{h_{i}}{2} = \frac{- 40}{20}$

$h_{i} = - 4 c m$

Inverted image of 4 cm is formed.

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A 2 cm high object is placed at a distance of 20 cm from a concave mirror. A real image is formed 40 cm from the mirror. Calculate the focal length of the mirror and the size of the image. [3 MARKS]

Problem: 3 Marks Given: u=−20cm v=−40cm We know Mirror formula 1f=1v+1u 1f=1−20+1−40 f=−13.3cm Focal length of the mirror is 13.3 cm We know hiho=−vu hi2=−4020 hi=−4cm Inverted image of 4 cm is formed.