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Waves moving across a boundary
Here's an example of light waves refracting into a glass block.
The speed of light in glass is slower than in air, so using the idea of 'Speed Away', the ray must 'Slow Towards' the normal line.
This means that the angle of refraction is less than the angle of incidence and the wavelength of light decreases.
Note that the frequency of the light (the number of waves going past each second) remains the same - i.e. the same colour of light (as it is frequency which determines the colour of light).
GCSE Keywords: wave speed, refraction, direction, frequency, wavelength