Question

Two thin lenses of power +5.5D and -3.5D are placed in contact. Find the

power and focal length of the lens combination. ​

Answer 1

Answer:

Total power=p1+p2

=5.5+(-3.5)

=5.5-3.5

=2D

Focal length=1/total power

f=1/2

f=0.5m=50cm

Answer 2

Answer:

Given:

Power of one lens(p1)=+5.5D

Power of another lens(p2)= - 3.5D

To find the power and focal length of the lens combination

Solution:

Power of lens in combination is calculated as,

$power(p) = p 1+ p2$

$power(p) = 5.5 - 3.5$

P = 2 D

Again,

Focal length(f)=?

We have,

$power(p) = \frac{1}{f}$

$2 = \frac{1}{f}$

$f = \frac{1}{2}$

$f = 0.5m$

Therefore, the pwer and focal length of the lens in combination are 2D and 0.5m.