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

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

Options:

Correct Answer: 5 D

Solution:

Power (P) = 1/f (in meters). f = 20 cm = 0.2 m, so P = 1/0.2 = 5 D.

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

A convex lens has a focal length of 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, where P is the power in diopters (D) and f is the focal length in meters.
Step 2: Convert the focal length from centimeters to meters. Since the focal length is given as 20 cm, we convert it to meters by dividing by 100. So, 20 cm = 20/100 = 0.2 m.
Step 3: Substitute the focal length in meters into the power formula. Now we have P = 1/0.2.
Step 4: Calculate the power. 1 divided by 0.2 equals 5. Therefore, P = 5 D.

Lens Formula – Understanding the relationship between focal length and power of a lens.
Unit Conversion – Converting focal length from centimeters to meters to calculate power.