• All waves, whether transverse or longitudinal, can be?reflected?and?refracted
• Reflection occurs when:

A wave hits a boundary between two media and does not pass through, but instead stays in the original medium

An identical image of the tree is seen in the water due to reflection

• Refraction occurs when:

A wave passes a boundary between two different transparent media and undergoes a change in direction

Waves can change direction when moving between materials with different densities

• Angles are measured between the wave direction (ray) and a line at 90 degrees to the boundary
  • The angle of the wave approaching the boundary is called the?angle of incidence (i)
  • The angle of the wave leaving the boundary is called the?angle of reflection (r)

   

• The angles are the?same, so the law of reflection can be written:

Angle of incidence (i) = Angle of reflection (r)

Angle of incidence and angle of reflection

Reflection Ray Diagrams

• Angles are measured between the wave direction (ray) and a line at 90 degrees to the boundary
  • The angle of the wave approaching the boundary is called the?angle of incidence (i)
  • The angle of the wave leaving the boundary is called the?angle of reflection (r)

   

• The?law of reflection?states that these angles are the same

Ray diagram of reflection of a wave at a mirror

• When drawing a ray diagram an arrow is used to show the direction the wave is travelling
  • An?incident?ray has an arrow pointing?towards?the boundary
  • A?reflected?ray has an arrow pointing?away?from the boundary

   

• The?angles?of?incidence?and?reflection?are usually labelled?i?and?r?respectively and measured from the?normal

Refraction Ray Diagrams

• Refraction occurs when light passes a boundary between two different transparent media
• At the boundary, the rays of light undergo a?change in direction
• The direction is taken as the angle from a hypothetical line called the normal
  • This line is perpendicular to the surface of the boundaries and is usually represented by a straight dashed or dotted line

   

• The change in direction depends on the difference in density between the two media:
  • From less dense to more dense (e.g air to glass), light bends?towards?the normal
  • From more dense to less dense (e.g. glass to air), light bends?away?from the normal
  • When passing along the normal (perpendicular) the light?does not bend?at all

   

How to construct a ray diagram showing the refraction of light as it passes through a rectangular block

• The change in direction occurs due to the change in speed when travelling in different substances
  • When light passes into a?denser?substance the rays will?slow down, hence they bend towards the normal

   

• The only properties that change during refraction are speed and wavelength – the?frequency?of waves?does not change
  • Different frequencies account for different?colours?of light (red has a low frequency, whilst blue has a high frequency)
  • When light refracts,?it does not change colour?(think of a pencil in a glass of water), therefore, the frequency does not change

   

Step 1: Draw a parallel ray on the left

Step 2: Draw the refracted ray at the first surface

• • As the ray?enters?the block it bends?towards?the normal since it is going into a denser material
  • In this case, the angle of refraction is?smaller?than the angle of incidence

   

Step 3: Draw the refracted ray at the second surface

• • As the ray?leaves?the block it bends?away?from the normal
  • In this case, the angle of refraction is?larger?than the angle of incidence