Experiment – Properties of EM waves
Using a light kit, three slit card, power pack and reflective surfaces, complete each activity
below. Your teacher will show you how to set up the light kit appropriately.
To finish this task today, you need to complete each activity below. You will be required to
sketch a ray diagram to represent what you see for each activity. A ray diagram is a diagram
that traces the path of light from its source. On the diagram rays (lines with arrows) are
drawn for the incident ray and the reflected ray. Below is an example of a ray diagram,
showing a ray of light reflecting off a surface.
All diagrams must be drawn in pencil.
Activity One:
Define the following terms
 Incident ray:

Reflected ray:

Ray diagram:

Angle of incidence:

Angle of reflection:

Normal:
Activity Two: Reflection
When an incident wave hits an obstacle, it bounces back. This is called a reflection.
When an incident wave hits a straight wall, the wave is reflected back at an angle equal to its
approach. Draw a diagram below of a wave reflecting off a mirror. In your diagram make
sure you indicate the angle of incidence, normal and the angle of reflection.
Activity Three: Refraction.
When an incident wave enters a new medium, such as glass it changes speed. Its wavelength
also changes, but the frequency doesn’t. In the diagram below, the waves slow down in the
new medium. Their wavelengths get shorter, but the number of peaks passing in a second
stays the same.
What is refraction?
Draw a diagram below of a wave refracting through a plastic block (at an angle). In your
diagram include the incident ray, the refracted ray, angle of incidence and the angle of
refraction.
Activity Four: Scattering
Scattering is a phenomenon where a wave
is redirected in many different directions.
For example, when sunlight hits our
atmosphere, the molecules of air cause the
light to be redirected in numerous
directions. Blue is scattered the most,
which is why the sky appears blue.
Draw a diagram to explain wave scattering, as an incident wave hits a rough surface
and is redirected in numerous directions.
HINT: to help model this, crumple up a piece of aluminium foil and shine a beam of light
onto it (use the three slit card).
Activity Five: Lenses
Lenses can be used to change the direction of a wave.
Define the following terms
 Concave lens:
 Convex lens:
 Focus:
 Focal length:
Draw a diagram below of a wave refracting through a concave lens. In your diagram
include the incident rays, the focus and the focal length. It can be difficult to find the focus of
a concave lens as it is not obvious but it can be found by tracking back any reflected waves.
Draw a diagram below of a wave refracting through a convex lens. In your diagram
include the incident rays, the focus and the focal length.
Activity Six: Curved Mirrors
Like lenses, curved mirrors can be used to change the direction of a wave. Like lenses, curved
mirrors will create a focus and a focal length.
Define the following terms
 Concave mirror:
 Convex mirror:
Concave mirrors produce magnified images of an object (like looking into the back of a
spoon). Draw a diagram below of a wave reflecting off a concave mirror. In your diagram
include the incident rays, the focus and the focal length.
Convex mirrors are useful when wide views are needed as they gather rays from a wide area
(they are often used in shops for security purposes). Draw a diagram below of a wave
reflecting off a convex mirror. In your diagram include the incident rays, the focus and the
focal length. In this case, the focus is behind the mirror.