A biconvex lens has a radius of curvature of 30 cm on both sides. What is the fo

Practice Questions

Q1
A biconvex lens has a radius of curvature of 30 cm on both sides. What is the focal length of the lens if the refractive index is 1.5?
  1. 10 cm
  2. 15 cm
  3. 20 cm
  4. 25 cm

Questions & Step-by-Step Solutions

A biconvex lens has a radius of curvature of 30 cm on both sides. What is the focal length of the lens if the refractive index is 1.5?
  • Step 1: Identify the radius of curvature (R) of the lens. In this case, R = 30 cm.
  • Step 2: Identify the refractive index (n) of the lens material. Here, n = 1.5.
  • Step 3: Use the lens maker's formula for a biconvex lens: f = R / (n - 1).
  • Step 4: Substitute the values into the formula: f = 30 / (1.5 - 1).
  • Step 5: Calculate the denominator: 1.5 - 1 = 0.5.
  • Step 6: Now substitute this value back into the formula: f = 30 / 0.5.
  • Step 7: Perform the division: 30 divided by 0.5 equals 60.
  • Step 8: Therefore, the focal length (f) of the lens is 60 cm.
  • Lens Maker's Formula – The formula used to calculate the focal length of a lens based on its radius of curvature and refractive index.
  • Refractive Index – A measure of how much light bends when entering a material, affecting the lens's focal length.
  • Radius of Curvature – The distance from the lens's surface to its center of curvature, influencing the lens's optical properties.
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