Total Internal Reflection is a free interactive simulation of total internal reflection and critical angle behaviour in glass for GCSE Physics (Edexcel IGCSE 4PH1). Students vary the angle of incidence on a semi-circular glass block and triangular prism to find the critical angle and observe total internal reflection and dispersion. This is a required practical for Edexcel IGCSE 4PH1. No login required — includes a worksheet and self-marking quiz.
Aim: To investigate total internal reflection and find the critical angle for a glass block.
Results Table
θi (°)
Observation
Action
With the material set to Glass, set the angle of incidence to a small value (around 10°) and observe the ray at the flat face.
Slowly increase the angle of incidence, recording your observation (refracted, partially reflected, or totally internally reflected) at each step in the results table.
Keep increasing the angle until the refracted ray disappears and all the light is reflected back into the block. Note the angle at which this first happens.
Enter your best estimate of this critical angle in the box provided and press Check to see how close you were.
Repeat for a different material (e.g. Diamond or Perspex). How does the critical angle change, and how does this relate to the refractive index of the material?
Use the normal and protractor tools to measure the angle of incidence at which total internal reflection begins, and compare it with the value given by the simulation.
Aim: To investigate dispersion and total internal reflection in a triangular prism.
Observation Table
Angle (°)
Light type
Appearance
Action
With the light type set to White, set the angle of incidence to about 45° and observe the ray emerging from the prism. Record what you see.
Vary the angle of incidence and note when the beam begins to spread into a spectrum of colours.
Switch the light type to Single λ and set the wavelength slider to a short wavelength (blue/violet), then a long wavelength (red). Record the appearance at each wavelength.
Compare how much a blue ray bends compared with a red ray at the same angle of incidence. Which colour refracts more?
Use your observations to explain why white light spreads into a spectrum when it passes through a prism, but a single wavelength does not.