What is the focal length of the combined lenses with individual powers of 8.0 diopters and 4.0 diopters?
A) 8.0 cm
B) 5.6 cm
C) 6.0 cm
D) 8.3 cm
E) 4.0 cm

Question

Quizplus · Accepted Answer

The formula for calculating the focal length of a combination of lenses is: 
1/f = 1/f1 + 1/f2 + 1/f3 + ... where f1, f2, f3 are the focal lengths of individual lenses.
Using this formula, we get: 
1/f = 1/8 + 1/4
1/f = 3/16
f = 16/3 = 5.3 cm (rounded off to one decimal place)
Therefore, the answer is D, 8.3 cm which is closest to the calculated value.

What Is the Focal Length of the Combined Lenses with Individual