Question

A student conducts an experiment using a convex lens. He places the object at a distance of 60 cm in front of the lens and observes that the image is formed at a distance of 30 cm behind the lens. The power of the lens is
0.005 diopter
0.05 diopter
5 diopter
50 diopter

Answer 1

Given:

A student conducts an experiment using a convex lens. He places the object at a distance of 60 cm in front of the lens and observes that the image is formed at a distance of 30 cm behind the lens.

To find:

Power of lens ?

Calculation:

Applying Len's Formula:

$\rm \: \dfrac{1}{f} = \dfrac{1}{v} - \dfrac{1}{u}$

$\rm \implies \: \dfrac{1}{f} = \dfrac{1}{30} + \dfrac{1}{ 60}$

$\rm \implies \: \dfrac{1}{f} = \dfrac{2+ 1}{60}$

$\rm \implies \: \dfrac{1}{f} = \dfrac{3}{60}$

$\rm \implies \: f = 20 \: cm$

$\rm \implies \:P = \dfrac{100}{ f( \: in \: cm) }$

$\rm \implies \:P = \dfrac{100}{ 20}$

$\rm \implies \:P = 5 \: D$

So, power of lens is 5D.

Answer 2

Given:

A student conducts an experiment using a convex lens. He places the object at a distance of 60 cm in front of the lens and observes that the image is formed at a distance of 30 cm behind the lens.

To find:

Power of lens ?

Calculation:

• Applying Len's Formula:

$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$

$= > \frac{1}{f} = \frac{1}{30} + \frac{1}{60}$

$= > \frac{1}{f} = \frac{2 + 1}{60}$

$= > \frac{1}{f} = \frac{3}{60}$

$= > f = 20 \: cm$

$= > p = \frac{100}{f(in \: cm)}$

$= > p = \frac{100}{20}$

$p = d$