Question

2 thin lenses of power plus 2 dioptre & -1.5 dioptre are placed in contact .find the

1-power?

2-focal length of the combination?

3- also , state nature of formed by the combination of these lenses?

Answer 1

HELLO DEAR,

we know that:-

f=1/p

where,

p=power

f = focal length

(1) :-

(a) given that;-

p=+2D

using the the formula

we get,

1/f=2

f=1/2

f=0.5m =50cm

the lens is convex lens of focal length= 0.5m = 50cm

(b) given that;-

p= -4D

using the the formula

we get,

1/f= -4

f= 1/-4

f= -0.25m = -25cm

the lens is concave lens of focal length= -0.25m = -25cm

(2) given that;-

u = -100cm = -1 m

and f=( 0.5m) for first lens

we know that:-

lens Formula

now put the values

we get,

and

magnification=

(b) for second lens

given that;-

u = -100cm = -1 m

and f= (-0.25m) for second lens

we know that:-

lens Formula

and

magnification is

I HOPE ITS HELP YOU DEAR