A concave mirror for face viewing has focal length of 0.4 m. The distance at which you hold the mirror from your face in order to see your image upright with a magnification of 5 is :

  • Option 1)

     0.24\: m

  • Option 2)

    1.60\: m

  • Option 3)

    0.32\: m

  • Option 4)

     0.16\: m

Answers (1)

\frac{1}{v}-\frac{1}{u}=\frac{1}{f} \: \: \:\; \Rightarrow \frac{1}{v}=\frac{1}{f}+\frac{1}{u}

m=\frac{v}{u}

\frac{1}{m}=\frac{u}{v}

\frac{1}{m}=u\left [ \frac{1}{f}+\frac{1}{u} \right ]

\frac{1}{m}=\frac{u}{f}+1

u=f\left ( 1-\frac{1}{m} \right )

u=f\left ( 1-\frac{1}{m} \right )

u=\left ( 0.4 \right )\left ( 1-\frac{1}{5} \right )

u=\left ( 0.4 \right )\left ( .8 \right )

u=.32\; m

 

 


Option 1)

 0.24\: m

Option 2)

1.60\: m

Option 3)

0.32\: m

Option 4)

 0.16\: m

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