A convex lens of focal length 15 cm is placed at the origin with its optical axis along the x-axis. A ray of light given by y = 1 - x/3 is incident on the lens. The equation of the refracted ray is y = -0.1mx + c (x and y in cm). Find m.

Question

G1 Physics · Accepted Answer

At the lens plane x=0, the incident ray is at height y=1 cm and has slope -1/3. For a thin lens, the paraxial ray slope changes by -y/f = -1/15. Hence the refracted slope is -1/3 - 1/15 = -2/5 = -0.4. Given refracted slope = -0.1m, we get m=4.