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  • Tell me? A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is:

A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is:

  • Option 1)

    15 cm

  • Option 2)

    2.5 cm

  • Option 3)

    5 cm

  • Option 4)

    10 cm

 

Answers (1)

best_answer

As we discussed in

Consider point A:

\mu = -20 cm, \:\:f=\:-10cm

From mirror formula \frac{1}{V_{A}}=\frac{1}{f}-\frac{1}{\mu_{A}}

\frac{1}{V_{A}}=\frac{-1}{10}+\frac{1}{20}=\frac{-1}{20}

V_{A}=-20cm

Hence image will form at A itself.

For B

\mu_{B}=-30cm\:\:\:\:f=-10cm

\frac{1}{V_{B}}=\frac{1}{f}-\frac{1}{\mu _{B}}= \frac{-1}{10}+\frac{1}{30}=\frac{-2}{30}

V_{B}=-15cm

\therefore size of image = \left | V_{A}-V_{B} \right |

= 5 cm.

 


Option 1)

15 cm

This option is incorrect.

Option 2)

2.5 cm

This option is incorrect.

Option 3)

5 cm

This option is correct.

Option 4)

10 cm

This option is incorrect.

Posted by

divya.saini

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