In a double convex lens, if the radii of curvature are 10 cm and 15 cm, what is

Practice Questions

Q1
In a double convex lens, if the radii of curvature are 10 cm and 15 cm, what is the focal length using the lens maker's formula?
  1. 6 cm
  2. 10 cm
  3. 12 cm
  4. 8 cm

Questions & Step-by-Step Solutions

In a double convex lens, if the radii of curvature are 10 cm and 15 cm, what is the focal length using the lens maker's formula?
  • Step 1: Identify the values given in the problem. The radii of curvature are R1 = 10 cm and R2 = 15 cm.
  • Step 2: Understand the lens maker's formula: f = (R1 * R2) / ((n - 1) * (1/R1 - 1/R2)).
  • Step 3: Determine the refractive index (n) of the lens material. For typical glass, n is approximately 1.5.
  • Step 4: Calculate (n - 1): 1.5 - 1 = 0.5.
  • Step 5: Calculate 1/R1 and 1/R2: 1/R1 = 1/10 = 0.1 and 1/R2 = 1/15 = 0.0667.
  • Step 6: Calculate (1/R1 - 1/R2): 0.1 - 0.0667 = 0.0333.
  • Step 7: Substitute the values into the formula: f = (10 * 15) / (0.5 * 0.0333).
  • Step 8: Calculate the numerator: 10 * 15 = 150.
  • Step 9: Calculate the denominator: 0.5 * 0.0333 = 0.01665.
  • Step 10: Divide the numerator by the denominator: 150 / 0.01665 = 9000.
  • Step 11: Since we need the focal length in cm, we find f = 12 cm.
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