High School Dude
13th August 2006 - 01:37 PM
For my science homework, I have to calculate the size of a shadow on a screen.
The object is a vertical pencil 15cm high which is 30cm away from a small spotlight which is almost level with the pencil. The screen is 1m away from the spotlight.
Please, I need help. Is there some sort of formula for calulating the size of a shadow formed by a certain object aginst a screen.
13th August 2006 - 07:14 PM
Think about triangles. Light spreads in straight lines, so the source of the light is in a straight line with all of shadows of the top of the pencil. Also, the source of the light is in a straight light with all of the shadows of the bottom of the pencil. So if the screen and the pencil are parallel, we have a situation of similar triangles. Therefore the problem reduces to one of units and ratios.
+---------+ X / 1 m (at screen)
+----+ 15 cm / 30cm (at pencil)
X = 1 m * 15 cm / 30 cm = 100 cm * 1/2 = 50 cm.
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