A thin lens has a focal length of 20 cm. What is the power of the lens?

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Question: A thin lens has a focal length of 20 cm. What is the power of the lens?

Options:

Correct Answer: +5 D

Solution:

Power (P) is given by P = 1/f (in meters). Thus, P = 1/0.2 = +5 D.

A thin lens has a focal length of 20 cm. What is the power of the lens?

A thin lens has a focal length of 20 cm. What is the power of the lens?

Step 1: Understand that the focal length (f) of the lens is given as 20 cm.
Step 2: Convert the focal length from centimeters to meters because the formula for power uses meters. 20 cm = 20/100 = 0.2 meters.
Step 3: Use the formula for power (P) of a lens, which is P = 1/f, where f is the focal length in meters.
Step 4: Substitute the value of f into the formula: P = 1/0.2.
Step 5: Calculate the power: P = 1/0.2 = 5.
Step 6: Since the lens is a thin lens, the power is positive, so we write it as +5 D (diopters).

Lens Power – The power of a lens is the reciprocal of its focal length measured in meters, expressed in diopters (D).