In: Physics
An early method of measuring the speed of light makes use of a rotating slotted wheel. A beam of light passes through a slot at the outside edge of the wheel, as in the figure, travels to a distant mirror, and returns to the wheel just in time to pass through the next slot in the wheel. One such slotted wheel has a radius of 8.8 cm and 100 slots at its edge. Measurements taken when the mirror is L = 1100 m from the wheel indicate a speed of light of 3.0 x 105 km/s. (a) What is the (constant) angular speed of the wheel? (b) What is the linear speed of a point on the edge of the wheel?
a) Here, t = 2L/c
= 2 * 1100/(3 * 108)
= 7.33 * 10-6 s
theta = (2pi)/100
= 0.0628 rad
Thus, the (constant) angular speed of the wheel = theta/t
= 0.0628/(7.33 * 10-6)
= 8567.53 rad/s
b) the linear speed of a point = r * w
= 0.088 * 8567.53
= 753.94 m/s