Question

(a) Two lenses have powers of (i) + 2D and (ii) -4D. What are the nature and focal length of each lens? (b) An object is kept at a distance of 100 cm from each of the above lenses. Calculate the (i) image distance and (ii) magnification in each of the two cases.
Pls, help me......

Answer 1

Answer:

given = 2 Lenses have power +2D and -4D

to find = distance and magnification in both cases.

solution :-

focal length = 100/2 cm = 50

the lenses is convex lens of focal length =50cm

the focal length = 100/p = 100/-4= -25

now,

for power of lenses +2D

u= -100 , f =+50

v=?

use the lense formula ,

1/f = 1/v-1/u

1/v = 1/40 -1/100

1/v = 60/4000

1/v= 400/6 =66.6 cm

magnification = m = -v/u

= -66.6/100

m= 0.66

now, for power of lenses -4D

1/f =1/v-1/u

1/v = 1/f +1/u

1/v = 1/--25 - 1/100

1/v= -125/2500

v= -2500/125

v2= -20cm

mqgnification = -v/u

m = -(-20/-100)

m= -1/5

m= 0.2