Calculate the focal length of a reading glass of a person if his distance of distinct vision is $75 c m$ :

25.6 c m

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37.5 c m

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75.2 c m

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100.4 c m

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Solution

The correct option is A $37.5 c m$
Distance of distinct vision of person , $v = - 75$ cm
Object distance , $u = - D = - 25$ cm

Using lens formula: $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

$∴$ $\frac{1}{- 75} - \frac{1}{- 25} = \frac{1}{f}$

$⟹$ $f = \frac{75}{2} = 37.5$ cm

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Calculate the focal length of a reading glass of a person if his distance of distinct vision is 75 cm :

The correct option is A 37.5 cmDistance of distinct vision of person , v=−75 cmObject distance , u=−D=−25 cmUsing lens formula: 1v−1u=1f∴ 1−75−1−25=1f ⟹ f=752=37.5 cm

Calculate the focal length of a reading glass of a person if his distance of distinct vision is $75 c m$ :

The correct option is A $37.5 c m$
Distance of distinct vision of person , $v = - 75$ cm
Object distance , $u = - D = - 25$ cm

Using lens formula: $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

$∴$ $\frac{1}{- 75} - \frac{1}{- 25} = \frac{1}{f}$

$⟹$ $f = \frac{75}{2} = 37.5$ cm