Question

Two lenses have powers of +2 D and -4 D. What is the nature and focal length of each lens. An object is kept at a distance of 100 cm from each of the above lenses, calculate the image distance and magnification in each of the two cases. (class 10)

Answer 1

Explanation:

1D = 1/f(m)

2 = 1/f(m)

f = 1/2

f = 0.5 m = 50 cm

-4 = 1/f(m)

f = 1/-4

f = 0.25 m = 25 cm

u = 100 cm for lense 1 & 2

for lens 1 ,

1/v = 1/f - 1/u

= 1/50 - 1/100

= 2/100 - 1/100

= 2-1/100

= 1/100

v = 100 cm = 1 m

for lens 2 ,

1/v = 1/f - 1/u

= 1/25 - 1/100

= 4/100 - 1/100

= 4-1/100

= 3/100

v = 100/3 = 33.3 ~ 33 cm =

hope it helps