Investigation to find the change in the speed of light through perspex.

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Investigation to find the change in the speed of light through perspex

Aim

   I intend to investigate the change in the speed of light in perspex. I intend to do this by passing a narrow ray of light through a D-block of Perspex, by using the same concepts and ideas as Snell’s Law.

Background Information

   Light is an electromagnetic wave. The speed of light depends on the medium through which it propagates: it goes fastest in vacuum, almost as fast in air but considerably slower in glass. The speed of light in a vacuum has been given its own symbol: c. The speed of light in any other material is denoted with v. The ratio of the two is known as the refractive index with the symbol n.

   When light goes from one medium to another, it doesn’t only change its speed. Part of the incident light is reflected, and the remainder is transmitted. The transmitted light is generally also deviated or refracted. It was found experimentally by Descartes and by Snell, some 400 years ago that:

• The incident, reflected and refracted ray all lie in the same plane

• The angles of incidence θ a and refraction θ b and the refractive indices na and nb of the media are related through what has become known as Snell’s Law:

   Snell’s Law =

the refractive index of the medium light is passing into

the refractive index of the medium light is passing out of

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= Sin(i)/Sin(r).

Apparatus

Perspex block (semi-circular)

Protractor sheet (A4)

Lens

Collimator

Optical pins

Power pack

Method

  • First we gathered all the required equipment.
  • Then we set it up by placing the perspex d-block on the A4 protractor paper and plugged in the ray box into the mains.
  • We then shone the ray of light at numerous different angles through the curved surface of the block.
  • At every angle from 5-40 in 5° intervals we recorded the angle of refraction and then repeated the measurement once more to ensure accuracy. This is reflected in ...

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This is a well structured and well written result. 1. The sources of information need to be referenced. 2. The word 'proved' is used many times and needs to be removed. 3. The conclusion needs to explain the results using researched information. ****