Question

An equiconvex lens has r=40cm and 10cm thick in the middle if refractive index of lens is 1.2 then determine postion of image from the lens

Answer 1

Answer:

Answer:

Correct answer is 22 rad/s

Explanation:

n=3.5 r. p. s.

ω =2πn =2×π×3.5 =7 ×22/7 which is approximately equal to 22 rad/s.

Answer 2

Given:

• Refractive index of lens $\mu_r = 1.2$

• Radius of lens $r = 20cm$

• Thickness of lens $d = 10cm$

To Find:

• Find the position of the image far away from the lens.

Solution:

We know that,

The focal length of a thick lens is given by

The Lens' Maker Formula-

         $\frac{1}{f} = ( \mu - 1) (\frac{1}{R_1} - \frac{1}{R_2} + \frac{(\mu - 1)d}{ \mu R_1 R_2} )$

        $\frac{1}{f} = ( 1.2 - 1) (\frac{1}{20} - \frac{1}{-20} + \frac{(1.2 - 1)10}{ 1.2 \times 20 \times 20} )$

         $\frac{1}{f} = ( .2) (\frac{1}{20} + \frac{1}{20} + \frac{1}{ 240} )$

         $\frac{1}{f} = ( .2) (\frac{1}{20} + \frac{1}{20} + \frac{1}{ 240} )$

         $\frac{1}{f} = 0.2 (0.05 + 0.05 + 0.0041) \\\frac{1}{f} = 0.020$

         $f = 50 cm$

Hence the image of object far from lens is formed at its focus, that is, at a distance $50cm$