Refraction of waves

• What happens when waves move from one medium to another?

  Change speed and change direction
• What happens when light is passed from air into glass?

  The velocity of light decreases (light wave slows down), this causes the direction of the wave to change and bends toward the normal. Once through the glass, the velocity of light increases and bends away from the normal. This causes the image of an object to appear to have shifted position.
• When can refraction happen?

  When any wave changes speed as it passes from one medium to another. However, if the waves enter or leave the medium at right angles to the surface (along the normal) then they do NOT change direction.
• What is a wavefront?

  An imaginary line that connects all the same points in a set of waves. For example, wavefronts connecting the peaks of each wave.
• Why do light waves change direction (using wavefronts)when passing from one medium to another using air and glass?

  When light waves move from air into glass, the corner of the wavefronts closer to the glass slow down first. This causes those parts of the wavefronts to get closer together meaning their wavelength decreases. This causes the waves to change direction towards the normal. As wave passes back to the less dense material the corner of the wavefront closest to the glass speeds up, this causes the wavelength to increase and causes it to refract away from the normal.
• What happens when wavefronts approach along the normal?

  The waves slow down as they pass into a more dense material, however the whole wavefront slows down at the same time meaning no refraction occurs.