A 3 cm high object is placed at a distance of 80 cm from a concave lens of focal length 20 cm. Find the position and size of the image.

0.1 cm

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0.4 cm

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0.2 cm

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0.6 cm

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Solution

The correct option is D
0.6 cm

Here, u = - 80 cm, f = - 20 cm

Using the len's formula, $\frac{1}{v}$ - $\frac{1}{u}$ = $\frac{1}{f}$

$\frac{1}{v}$ - $\frac{1}{- 80}$ = $\frac{1}{- 20}$

v = -16 cm

Magnification, m = $\frac{h^{/}}{h}$ = $\frac{v}{u}$ = $\frac{- 16}{- 80}$ = $\frac{1}{5}$

$h^{/}$ = $\frac{h}{5}$ = $\frac{3.0}{5}$ = 0.6 cm

Length of the image is 0.6 cm. Positive sign shows that the image is erect.

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A 3 cm high object is placed at a distance of 80 cm from a concave lens of focal length 20 cm. Find the position and size of the image.

The correct option is D 0.6 cm Here, u = - 80 cm, f = - 20 cm Using the len's formula, 1v - 1u = 1f 1v - 1−80 = 1−20 v = -16 cm Magnification, m = h/h = vu = −16−80 = 15 h/ = h5 = 3.05 = 0.6 cm Length of the image is 0.6 cm. Positive sign shows that the image is erect.