How the Length of the Block That the Light Travels Through Varies the Lateral Displacement.

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Nicholas Robson        Teme House        Physics coursework

Physics coursework Experiment: How the Length of the Block That the Light Travels Through Varies the Lateral Displacement.

Planning

        What is REFRACTION?

Refraction is how, in this case, a beam of light is slowed down or gets faster when it goes from one medium to another. In this case, the light will be slowed down when it goes from air into glass and speeds up as it goes back into air. So it goes from a less dense medium into a denser medium and back again. It will bend towards the normal when the light goes in to the glass block.

        What is LATERAL DISPLACEMENT?

Lateral displacement is the amount of movement that the ray of light has done whilst going through a different medium to when it started. In this case, the lateral displacement is affected by the glass, but even air slightly bents the light. The only medium that doesn't affect the light is a vacuum.

         

         L

The Experiment:

Safety:

As the lights will be off, one must be careful not to trip an anything on the floor.

Hypothesis:

My hypothesis is that as the as the length of the block grows (L), the Lateral displacement grows as well. This is because the glass block drags the ray of light towards the normal. This means that the more that there is that moves it away from the ray that would be there if there were no block, and so the lateral displacement grows as well, so that when the dragging away is doubled, so will the lateral displacement. Because of this, I think my results will be directly proportionate.

Measurements, Fair Test and How to be accurate

The measurements of the block are 2cm x 6 cm x 11 cm, and I will be using two blocks. The blocks will be put together, so that I can get more than three results. The Sizes of the amount of glass that the ray passes through will be 2cm, 4cm, 6cm, 8 cm, 11 cm, 12 cm, 13 cm, 17 cm and 22 cm. I know that it is possible to use 2 cm, and that the Lateral displacement will not be too low, because in an experiment beforehand, the lateral displacement was 34 mm, with size L as six, and the angle of incidence as 60 degrees. So if I used the size L=2, the answer will be about 11 mm, because I think that the answers will be directly proportionate. This will be the only variable, in order that it may be a fair test. The equipment will be taped down so that all of the measurements are equal, and protractors will be used for 90 degrees. The problem with using two blocks together is that there will be air trapped in the block, and so that the light will be changed for a fraction of a length because it moves away from the normal and back again. Fortunately, the distances are so small, that the distance will be almost negligible. The other problems with accuracy are that the pencil will have to be sharp to get a smaller line and point, and that the light ray is quite thick. Because of these things, I have to use the bottom of the ray for measurement. I will use that angle i=60 degrees, because then the measurements of the lateral displacement will be larger than if I used 45 degrees. In order that my results may be reliable, I will take two measurements for the lateral displacement and find the average. If one looks out of place, then I will take a third and find the average of the closest results.

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Equipment

The equipment that I will use is as follows: 2 glass blocks (rough measurements being

2cm x 6cm x 11cm), Ruler calibrated in millimetres, HB pencil, protractor, ray box, paper and a mains supply.

How the table will look

I will plot a graph and fill in a table of the length of the glass block and the length of the displacement.

 

The numbers on the left side of the table depend on the lengths of the sides.

The range of my results will be from 10 mm to about 140mm. ...

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