Reflection (Oxford AQA IGCSE Physics): Revision Note

Law of Reflection

• All waves, whether transverse or longitudinal, can be reflected

• Reflection occurs when:

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

• Angles are measured between the wave direction (ray) and the normal

  • The normal is a construction line perpendicular to the surface of the boundaries and is usually represented by a straight dotted line

  • 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)

Light reflects from a surface

Reflection in a Plane Mirror

• When an object is placed in front of a plane mirror, an image of that object can be seen in the mirror

• The image will be:

  • the same size as the object

  • the same distance behind the mirror as the object is in front of it

  • virtual

  • upright

  • laterally inverted

• The formation of this image can be understood by drawing a ray diagram

Ray diagram of an object reflected in a plane mirror

• Light from the object hits the mirror and is reflected according to the law of reflection

angle of incidence = angle of reflection

• The reflected ray can be traced back forming a virtual ray

• This can be repeated for another ray travelling in a slightly different direction

• An image of the object will appear where these two virtual rays cross

• The type of image formed in the mirror is called a virtual image