Question

Two lenses of power + 2.50 D and -3.75 D are combined to form a compound lens. The focal length of  the new lens is​

Answer 1

Answer:

0.8m

Explanation:

power of the new lens = 2.5+(-3.75)= -1.25

1/f= -125/100

f= -100/125= 0.8m

Answer 2

Given:

Two lenses of power +2.50 D and -3.75 D.

To find:

The focal length of the new combined lens.

Formula to be used:

Power formula needs to be used to find the focal length that is

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

Solution:

Let's find out the combined power of the lenses, which will be:

= +2.50 + (-3.75)

= -1.25 D

The focal length of the new lens will be:

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

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

f = $\frac{1}{10}$

f = 0.1 m or 10 cm

Final answer:

Focal length of the combined lenses is 0.1 metres.