Question

A diverging lens has a focal length of 20 cm. Its power in diopters is:

A) 0.20
B) -0.20
C) 0.05
D) 20
E) -5
F) -20
G) 5
H) -0.05

Answer 1

The power of a diverging lens with a focal length of 20 cm is calculated by taking the reciprocal of the focal length in meters. Since the focal length of a diverging lens is negative, the power is also negative and equals -5 diopters.

Step-by-step explanation:

A diverging lens, which bends light rays away from its axis, has a negative focal length. The power of a diverging lens with a focal length of 20 cm is calculated by taking the reciprocal of the focal length in meters. Since the focal length of a diverging lens is negative, the power is also negative and equals -5 diopters.

When calculating the power of the lens in diopters (D), we need to convert the focal length in centimeters to meters by dividing 20 cm by 100 to get 0.2 m. The power in diopters is the reciprocal of the focal length in meters. Since the focal length is negative for a diverging lens, we take the reciprocal of -0.2 m to find the power.

Therefore, the power P = -1/0.2 m = -5 diopters (D). So, the correct answer is E) -5.