Question

A biconvex lens is formed by using a piece of plastic (n = 1.70). the radius of the front surface is 20 cm and the radius of the back surface is 30 cm. what is the focal length of the lens?

Answers

  1. The focal length of the lens is mathematically given as
    f = 17.15cm

    What is the focal length of the lens?

    Generally, the equation for focal length is mathematically given as
    1/f = (n-1)(1/R1 -1/R2)
    f: focal length of the lens
    n: refractive index of the lens
    R1 radius of the front surface
    R2 radius of the back surface
    R1(front surface) = 20cm
    R2(back surface) = 30cm
    n = 1.70
    therefore,
    1/f = (1.70-1)(1/20 -1/-30)
    1/f = 0.70 * 0.083
    1/f = 0.0581
    f = 17.15cm
    In conclusion, the focal length of the lens
    f = 17.15cm
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