The radius of curvature of the convex surface of a Plano-convex lens is 10cm. What is the focal length of the Plano-convex lens? (Here μ = 1.5)

• A. 10cm
• B. 20cm
• C. 15cm
• D. 5cm

To find the focal length of a Plano-convex lens, we can use the lens maker's formula. For a Plano-convex lens, the formula is given by:

Lens Maker's Formula

The formula is:

f = R / (μ - 1)

Where:

• f = focal length
• R = radius of curvature
• μ = refractive index of the lens material

Given Values

In this case:

• R = 10 cm
• μ = 1.5

Calculating the Focal Length

Now, substituting the values into the formula:

f = 10 cm / (1.5 - 1)

f = 10 cm / 0.5

f = 20 cm

Final Answer

The focal length of the Plano-convex lens is 20 cm. Therefore, the correct option is B. 20cm.