Department of Pre-University Education, KarnatakaPUC Karnataka Science Class 12
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A Man Uses a Concave Mirror for Shaving. He Keeps His Face at a Distance of 25 Cm from the Mirror and Gets an Image - Physics

Sum

A man uses a concave mirror for shaving. He keeps his face at a distance of 25 cm from the mirror and gets an image which is 1.4 times enlarged. Find the focal length of the mirror.

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Solution

Given,
Distance of the man's face (here, taken as object), u = −25 cm
According to the question, magnification, m = 1.4

\[m = \frac{A'B'}{AB} =  - \frac{v}{u}\] 

\[ \Rightarrow   1 . 4 =  - \frac{(v)}{- 25}\] 

\[\Rightarrow\frac{14}{10}=\frac{v}{25}\] 

\[\Rightarrow v=\frac{25 \times 14}{10}=35 \text{ cm }\]
Using equation of mirror, we get: 
\[\frac{1}{f} = \frac{1}{v} + \frac{1}{u}\]
`⇒ 1/f  = 1/35 - 1/25`
\[= \frac{5 - 7}{175} =  - \frac{2}{175}\] 
⇒ f = −87.5

Hence, the required focal length of the concave mirror is 87.5 cm.

  Is there an error in this question or solution?
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APPEARS IN

HC Verma Class 11, 12 Concepts of Physics 1
Chapter 18 Geometrical Optics
Q 8 | Page 412
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