In problem 99, in the workbook, your screen is only 1.2 m high, but you move it
ID: 1614881 • Letter: I
Question
In problem 99, in the workbook, your screen is only 1.2 m high, but you move it closer to the projector. It is only 2.5 m from the slide. What is the focal length of the lens in cm, if your image is in focus and fills the screen? Enter an integer. Round up or down correctly.
Thin Lenses Problem Description ,i ELT A side 24s0 mm high is to be projected so that its image fills a screen 1.80 m high The screen is 3.0 m from the slidenas. shown How far from the slide should the projectors lens be in order to form the image on the screen? What must be the focal length of the lens if the image is.to be in focus?Explanation / Answer
M = h ' / h
M = - 1.8 / 24 X 10-3
= - 75
M = - q / p = - 75
q = 75 p
p + q = 3
p + 75 p = 3
76 p = 3
p = 3 / 76
p = 3.95 X 10-2 m
p = 39.5 mm ( the distance )
1 / f = 1 / p + 1 / q
1 / f = 1 / p + 1 / 75 p
f = 75 / 76 p
f = 75 X 39.5 / 76
f = 38.98 mm ( focal length )