Question

A concave cosmetic mirror has a focal length of 40 cm . A 4.0-cm-long mascara brush is held upright 20 cm from the mirror.
a) Use ray tracing to determine the location of its image
b) What is the height of the image? Use ray tracing to determine.

Answer 1

The location of  image and the height of the image is mathematically given as

di = -40 cm

h=8 cm

The location of  image and the height of the image

upright and enlarged

Question Parameters:

Generally the equation for the   is mathematically given as

using mirror equation

1/f = (1/do) + (1/di)

Therefore

1/40 = (1/20) + (1/di)

di = -40 cm

Therefore, Magnification

m = -di/do = hi/h\

m = 40/20 = hi/4

m = 2 = hi/4

image height is

hi = 4*2

h=8 cm

upright and enlarged

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