10.2 Properties of Light and
Reflection
Reflection

When light (electromagnetic waves) hits a surface its
direction is changed


This change in direction is referred to as reflection.
Reflection can be seen best on surfaces that are mirrors
or have mirror like properties.
Rays of Light

Light travels along a medium.


A medium is a term that refers to a substance through which
light is traveling through (e.g. water, air)
Light will travel in a straight line as long as its moving
through the same medium


Therefore, if light is travel through air, it will travel in a straight
line
However, if light travels through air then through water, it may
no longer travel in a straight line.
Predicting the Path of Light

By understanding the properties of light and mediums we
can predict the path of light and also the formation of
shadows

A ray is used to predict the path of light


A ray is a straight line with an arrowhead that shows the
direction in which light waves are travelling.
Rays are commonly used in a process call ray tracing.
Ray Tracing

Ray tracing is the process of drawing rays from a light
source to one or more objects.

Shadows can be detecting using this strategy
Fermat’s Principle

Fermat’s principle predicts the path light will take after
reflecting from a surface or passing through more than
one medium (e.g. air to water)

Light will follow the shortest path possible

Leads to the laws of reflection
The Laws of Reflection

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A ray of light moving towards a surface is known as the
incident ray.
The angle of incidence is the angle between the
incident ray and a perpendicular (Normal) line at the
point where the ray touches the surface
The Laws of Reflection

The reflected ray begins at the point of contact and is at a right
angle to the incident ray.

The angle of reflection is the angle between the reflected ray
and the perpendicular (Normal) line.

The angle of incidence/ray is equal to the angle of reflection/ray

Laws of reflection
Drawing Ray Diagrams

Follow figure 10.14 and draw a ray diagram for:


An incident ray at 5 cm from the normal at a 30o angle
An incident ray at 10cm from the normal at a 20o angle
Homework Questions

Answer questions 2-3 on page 414
Images in Plane Mirrors

When light is applied to an object in a plane mirror, the
image of that object is formed on the other side.

Using the laws of reflection, one can predict the characteristics
of the image and where the eye sees the image.
Image
Four Characteristics of an Image

In general an image has four characteristics:
1.
Its location (i.e. closer than, farther than,
same distance)
2.
Orientation (upright or inverted)
3.
Size (same, smaller, or larger)
4.
Type (real or virtual)
E.g. Location (farther than)
E.g. Orientation (inverted)
Size (larger)
Type (real image)
Homework Questions

Answer questions on page 418` #1,2,4, 6,7