Required practical

Investigate refraction in rectangular blocks in terms of the interaction of electromagnetic waves with matter

There are different ways to investigate refraction in rectangular blocks. In this required practical activity, it is important to:

  • make and record the angles of incidence and the angles of refraction accurately
  • measure and observe the angle of refraction
  • use appropriate apparatus and methods to measure refraction and how it may be different for different substances

Aim of the experiment

To investigate refraction in rectangular blocks and find out how it is different for different substances

Method

The light ray as it enters the block, is refracted slightly, and then leaves the block. The smallest angles between the light ray and the block as the ray enters and leaves are the same size.
  1. Set up a ray box, slit and lens so that a narrow ray of light is produced.
  2. Place a 30 centimetre (cm) ruler near the middle of a piece of plain A3 paper. Draw a straight line parallel to its longer sides. Use a protractor to draw a second line at right angles to this line. Label this line with an ‘N’ for ‘normal’.
  3. Place the longest side of a rectangular acrylic polymer block against the first line. With the normal near the middle of the block, carefully draw around the block without moving it.
  4. Use the ray box to shine a ray of light at the point where the normal meets the block. This is the incident ray.
  5. The angle between the normal and the incident ray is called the angle of incidence. Move the ray box or paper to change the angle of incidence. The aim is to see a clear ray leaving the opposite face of the block.
  6. Using a pencil on the paper, mark the path of the incident ray with a cross and the ray that leaves the block with a cross at the point the ray leaves the block.
  7. Remove the block. Draw a line joining each cross to the point where the normal meets the block to show the paths of the light rays.
  8. Repeat steps 2 to 7 for different angles of incidence.
  9. Measure the angle of incidence and angle of refraction for each block.

Polymer blockGlass block
Angle of incidence (°)Angle of refraction (°)Angle of refraction (°)
.........

Analysis

Compare the angle of incidence with the angle of refraction for each block.

Evaluation

How do the differences in the angles of refraction for different materials depend on the materials themselves?

HazardConsequenceControl measures
Ray box gets hotMinor burns Do not touch bulb, allow time to cool
Semi-dark environmentIncreased trip hazardEnsure environment is clear of potential trip hazards before lowering lights
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