SPEED OF LIGHT
1. A wheel with 120 teeth is rotated at a uniform
speed and light passing through one slot is reflected back along its own path
from a mirror 20 km away. If the light is to return through the next slot,
determine the speed of rotation of the wheel. (Velocity of light = 3.0 x108
ms-1)
2. In Fizeau’s rotating wheel experiment the first
eclipse occurs when the angular velocity of the wheel is . Calculate the speed
at which
(a) the light will be visible again
(b) the second eclipse will occur, and
(c) the third eclipse will occur.
3. A rotating mirror method was used to measure the
velocity of light in a liquid.
Calculate the refractive index of the liquid using the
following data:
Velocity of light in air 3.0x108 ms-1
Number of
revolutions per second 600
Deflection of image 2.0 mm
Deflection of image 2.0 mm
Source to lens 1.50
m
Lens concave mirror 20
m
Lens to plane mirror 10
cm
4. In a
simple version of Foucault's apparatus for measuring the velocity of light the
distance between the rotating mirror and the concave reflector was 1 km, the
distance from the eyepiece to the rotating mirror was 5 m, the measured value
of the velocity of light was 2.98x108 ms-1.
What was the
speed of rotation of the mirror when the image was displaced through a distance of 20 mm?
5. In an experiment to measure the velocity of light
using Michelson’s rotating eight-sided prism the distance between the prism and
the distant reflector was 35 km.
If the speed of light is 3.0x108 ms-1,
calculate the least possible speed of rotation of the prism to give a steady
reflected signal at the eyepiece.
What is the next speed of rotation would give the same
effect.
6. If the velocity of light in a vacuum is 3.0x108
ms-1 m calculate its velocity in:
(a) water (refractive index 1.33),
(b) glass (refractive index 1.45), and
(c) diamond (refractive index 2.42).
