Light
Reflection
► Which of these materials can reflect light?
L.O: Describe reflection at a plane surface and
use the law of reflection.
► Light travels in straight lines (rays of light)
► When light rays fall on a plane surface (Example: mirror), these light rays will be
reflected.
L.O: Describe reflection at a plane surface and
use the law of reflection.
► The light ray falling on the plane surface is called the incident ray.
► The incident ray falls on the reflecting surface at an angle, this angle is called the
incident angle.
► However, the ray reflected from the surface is called the reflected ray.
► The reflected ray is reflected at an angle called the reflected angle.
► The incident angle is always equal to the reflected angle, this is called the law of
reflection.
L.O: Describe reflection at a plane surface and
use the law of reflection.
L.O: Describe reflection at a plane surface and
use the law of reflection.
► In order to be able to measure either the angle of incidence or reflection, we must
draw an imaginary line perpendicular (at 90 degrees) to the plane surface.
► This line is called the normal.
► We draw ray diagrams to help us understand reflection. (Previous Page)
Keywords
► Plane surface
► Incident ray
► Reflected Ray
► Angle of incidence
► Angle of reflection
► Normal
► Law of reflection
► Ray Diagram
Exercise
► Label the following diagram and mention its name:
L.O: Describe refraction of light at the boundary between air
and glass or air and water in terms of change of speed.
► If you look through a glass of water, the background that you see appears
distorted. Distorted means less clear.
► This distortion happens because of light refraction.
L.O: Describe refraction of light at the boundary between air
and glass or air and water in terms of change of speed.
► The material that light passes through is called a medium.
► Light travels at different speeds when it is passing through different media.
► This change in speed causes the light rays to change direction and become bent,
and so refraction takes place.
L.O: Describe refraction of light at the boundary between air
and glass or air and water in terms of change of speed.
► The speed of light in air is 300,000 kilometers per second.
► However, when light passes from air into water or glass, the light travels more
slowly. The table shows the different speeds of light in different media.
Medium Speed of light (kilometers per second)
Air 300,000
Water 225,000
Glass 200,000
L.O: Describe refraction of light at the boundary between air
and glass or air and water in terms of change of speed.
► The light ray entering from one medium to another is called the incident ray, it
enters with an angle called the angle of incidence.
► The light ray passing through the second medium is called the refracted ray, it
leaves the first medium with an angle called the angle of refraction.
L.O: Describe refraction of light at the boundary between air
and glass or air and water in terms of change of speed.
► As light passes from air into water or
glass, it slows down.
► This causes the incident ray to change
direction and bend towards the normal.
► This means that the angle of incidence
will be greater than the angle of refraction
as the angle of refraction will be closer to
the normal.
L.O: Describe refraction of light at the boundary between air
and glass or air and water in terms of change of speed.
► However, as light passes from water or
glass to the air, it speeds up.
► This causes the incident ray to change
direction and bend away from the normal.
► This means that the angle of incidence
will be smaller than the angle of
refraction, as the angle of refraction will
be further away from the normal.
Activity!
► https://phet.colorado.edu/sims/html/bending-light/latest/bending-light_all.html
Exercise
► Complete the following diagram:
Thank you!
