Finding minimum angular speed in Fizeau wheel experiment

[clairez93]

Homework Statement

In an experiment to measure the speed of light using the apparatus of Fizeau, the distance between light source and mirror was 11.45 km and the wheel had 720 notches. The experimentally determined value of c was 2.889 x 10^8 m/s. Calculate the minimum angular speed of the wheel for this experiment.

Homework Equations

c = 2d/t
t = theta/w

The Attempt at a Solution

2.998 x 10^8 m/s = 2(11450m) / t
t = 7.638 x 10^-5 s

7.368 x 10^-5 = (1/440 rev) / w
w = 9.091 rev/s
9.091 * 2pi = 57.12 rad/s

Book answer: 114 rad/s

 

[clairez93]

Sorry about the earlier empty message; I hit enter too early. I am not sure what mistake I have mdae in my calculations, and if someone could look it over and help me, it would be greatly appreciated.

 

[quantumdude]

7.368 x 10^-5 = (1/440 rev) / w

Why is $\theta$ equal to 1/1440 rev (I think that's what you meant). If there are 720 notches, then $\theta=1/720$ rev. That will give you the right answer.