An early method of measuring the speed of light makes use of a rotating slotted
ID: 1294869 • Letter: A
Question
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 9.4 cm and 230 slots at its edge. Measurements taken when the mirror is L = 600 m from the wheel indicate a speed of light of 3.0 x 10^5 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?
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 9.4 cm and 230 slots at its edge. Measurements taken when the mirror is L = 600 m from the wheel indicate a speed of light of 3.0 x 10^5 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?Explanation / Answer
The time to travel to the mirror and back was
t=450/3E+8
The distance from one slot to another is
2*pi*0.05/550
the time to rotate the distance was
t=2*pi/(w*550)
combine
2*pi/(w*550)=450/3E+8
solve for w
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