Question

What is the meant by power of lens? write its si unit.a student uses a lens of focal length 40 cm and another -20 cm.write the nature of lens and power of each lens.

Answer 1

Explanation:

the capacity of a lense to converge or diverge incident rays is called its power

its unit is dioptre (D)

For first student ;

f = 40 cm................(40/100=0.4m)

we know that

P = 1/f(m)

= 1/ 0.4

= 2.5 D

dor another student

f = - 20cm...............(0.2m)

similarly

P= 1/f(m)

= 1/0.2

= 5D