The Speed of Light Through Perspex
Planning
Light travels at different speeds through different mediums. The speed
of light in air is 300,000,000m/s. When light enters an optically
denser medium, it bends towards the normal (refracts). You can work
out the refractive index of by dividing the sine of the incidence
angle by the sine of the angle of refraction and then working out the
ratio of the two.
Sine i
Sine r
From this refractive index you can work out the speed of light through
the chosen medium by dividing the speed of light through air by the
refractive index.
300,000,000
Refractive index
Experiment:
Apparatus list:
Ray box
Power pack
Perspex D-Block
Pencil
Paper with degree markings.
[IMAGE]
Method:
· Set up apparatus as shown in diagram.
· Shine light ray through D-Block.
· Mark out position of incident ray and refracted ray.
· Measure angle I and angle r.
· Repeat a number of times changing the position of the ray box each
time.
To make it a fair test I will use the same apparatus every time and
make sure that the d block doesn't change position when I carry out
the experiment. I will repeat each reading twice to get an average,
making the experiment more accurate.
Prediction:
I think that the refracted ray will be refracted towards the normal
because Perspex is a denser medium than air. I believe that Perspex
will slow down the speed of light entering into it. I am confident
that the ray of light will refract towards the normal because I have
performed a number of experiments which are similar to this one. After
collecting results and working out the refractive index by using sine
i/ sine r, I think the answer will be a number close to 1.5 which is
the refractive index of glass. I think it will be a number close to
How am I going to make it a fair test I will use a clean flask for
as the “r-value” and “r” can be any value between -1 and +1. It can be
To make sure it is a fair test; the procedure is repeated a couple of
As I do this experiment the thing I am going to be changing is the
Put a label on each test tube. With a pencil, number each test tube from one to twelve.
Be sure to clean the syringe and measuring cylinder after every use to prevent cross contamination.
repeat the process 3 times in total to ensure a fair test. At the end
We will do this about 4 times and see the difference and see if there is any change.
What I Will Vary, Not Change To Keep A Fair Test & What I Will
List of the tests to be conducted, material to be tested, the location of sampling, the organization’s name that will perform the test, and the frequency of testing.
test is always your own serenity. If you don't have this when you start and maintain it while
The index of refraction is defined as the speed of light in vacuum divided by the speed of light in the medium. In this experiment, the index of refraction for the perspex is 1.50. Snell's Law relates the indices of refraction of the two media to the directions of propagation in terms of the angles to the normal. It refers to the relationship between the different angles of light as it passes from one transparent medium to another. When light passes from one transparent medium to another, it bends according to Snell's law which states: [IMAGE] where: n1 is the refractive index of the medium the light is leaving, n2 is the refractive index of the medium the light is entering, sin 2 is the is the incident angle between the light ray and the normal to the medium to medium interface, sin 1 is the refractive angle between the light ray and the normal to the medium to medium interface.