Question

How do your results from ray tracing compare to your results from using the thin-lens equation?

What is the focal length of a convex lens that produces an image 10 cm away with a magnification of -0.5? Show all calculations in your answer.

Answer 1

f = 6.66 cm

Step-by-step explanation:

For this exercise we will use the constructor equation

1 / f = 1 / p + 1 / q

where f is the focal length, p is the distance to the object and q is the distance to the image

the expression for magnification is

m = h '/ h = - q / p

with this we have a system of two equations with two unknowns, in the problem they give us the distance to the image q = 10 cm and a magnification of m = -0.5

-0.5 = - q / p

p = - q / 0.5

p = - 10 / 0.5

p = 20 cm

now we can with the other equation look for the focal length

1 / f = 1/20 + 1/10

1 / f = 0.15

f = 6.66 cm