# Refraction and diffraction

### Refraction

In 3AB, only qualitatively. Quantitatively is out of the syllabus.

• Refraction is the bending of a wave when it enters a medium with a different wave speed
• When light moves from a fast medium to a slow medium, it bends towards the normal
• When light moves from a slow medium to a fast medium, it bends away from the normal

REMEMBER:

From fast to slow, to the normal we go

##### Total internal reflection
• Occurs when
• The wave is going from a slower medium to a faster one
• the angle of incidence exceeds the critical angle
• The wave gets reflected rather than refracted
• If angle of incidence is equal to the critical angle, the wave refracts at 90o to the normal

### Diffraction

• The bending of a wave around small objects
• The spreading out of a wave beyond small openings

• Significant diffraction occurs when the wavelength is the same order of magnitude as the width of the opening or obstacle
• The greater the wavelength, the greater the diffraction
• The smaller the obstacle or opening, the greater the diffraction