13 April 2010

Optics



Problem 1.
A person stands 40 m from a flag pole. With a protractor at eye level, he finds the angle at the top of the flag pole with the horizontal is 25.0 degrees. How high is the flag pole? The distance from his feet to his eyes is 1.8 m. 
Solution: 
We draw the picture of the problem, where we show the angle 25 degree, the person's height, and the distance between the person and the pole.
From the right triangle ABC we can find the distance BC (we know the angle and we know the distance AB = 40 m):
The distance OB is equal to the height of the person (which is 1.8 m). Then we can find the whole height of the pole:
Problem 2. 
The frequency of yellow light is . Find the wavelength of yellow light. The speed of light is .
Solution: 
In this problem we need to use the relation between the frequency , wavelength , and the speed of the light (wave):
Then