An object is placed at a distance of - 10 cm- from the concave mirror and the image is formed -160- 20 cm- in front of the mirror- The focal length of the mirror is- - 203 cm- -20 cm- 320 cm- 15 cm-

The correct option is A 203 cm Here, u= 10 cm v= 20 cm Now, 1f=1u+ 1v 1f=1 10+1 20 f= 203 cm ...

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Standard IX

Physics

Mirror Formula

An object is ...

Question

An object is placed at a distance of $10 c m$ from the concave mirror and the image is formed $20 c m$ in front of the mirror. The focal length of the mirror is:

- \frac{20}{3} c m

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\frac{3}{20} c m

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15 c m

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- 20 c m

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Solution

The correct option is A $- \frac{20}{3} c m$
Here, $u = - 10 c m$ $v = - 20 c m$
Now, $\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$

$\frac{1}{f} = \frac{1}{- 10} + \frac{1}{- 20}$

$f = - \frac{20}{3} c m$

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An object is placed at a distance of 10cm from the concave mirror and the image is formed 20cm in front of the mirror. The focal length of the mirror is:

The correct option is A −203cmHere, u=−10cm v=−20cmNow, 1f=1u+1v1f=1−10+1−20f=−203cm

An object is placed at a distance of $10 c m$ from the concave mirror and the image is formed $20 c m$ in front of the mirror. The focal length of the mirror is:

The correct option is A $- \frac{20}{3} c m$
Here, $u = - 10 c m$ $v = - 20 c m$
Now, $\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$

$\frac{1}{f} = \frac{1}{- 10} + \frac{1}{- 20}$

$f = - \frac{20}{3} c m$