If the focal length of a lens is 20 cm, what is the power of the lens?

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Question: If the focal length of a lens is 20 cm, what is the power of the lens?

Options:

Correct Answer: +10 D

Solution:

Power (P) = 1/f (in meters). Here, f = 0.2 m, so P = 1/0.2 = +5 D.

If the focal length of a lens is 20 cm, what is the power of the lens?

If the focal length of a lens is 20 cm, what is the power of the lens?

Step 1: Understand that the power of a lens is calculated using the formula P = 1/f.
Step 2: Know that 'f' is the focal length of the lens, which is given as 20 cm.
Step 3: Convert the focal length from centimeters to meters. Since 1 meter = 100 centimeters, 20 cm = 20/100 = 0.2 m.
Step 4: Substitute the value of f into the formula. So, P = 1/0.2.
Step 5: Calculate the power. 1 divided by 0.2 equals 5.
Step 6: Write the final answer with the correct unit. The power of the lens is +5 Diopters (D).

Lens Power Calculation – The power of a lens is calculated using the formula P = 1/f, where f is the focal length in meters.