This document discusses different models for light, including rays and waves. It explores light traveling in straight lines and being reflected regularly. Light can be modeled as either particles or waves, and both views were debated among early physicists. Reflection, absorption, and transmission of light are also covered, noting no material is perfectly transparent and allowing some light to pass through while reflecting or absorbing the rest.

1. Modelling Simple Light
Properties
8.1 waves, particles, reflection, absorption, transmission

2. Is Light made of particles or is it a wave?
The giants of physics became embroiled in a famous ongoing scientific
debate that posed the question: Is light made up of particles or waves?
Over the coming weeks we will be investigating this question and will
see the very simplest behaviours of light can be readily modelled as
either particles or waves.

3. Light Travels in Straight Lines
The mechanism by which our eyes
and brain interpret a three-
dimensional world is complex, but it
relies on the assumption that light in
a uniform medium travels in straight
lines.

4. A Model - Rays
• A beam of light can be thought of as a bundle of rays. A strong light
source, such as the Sun, could therefore be thought of as producing a
very large number of light rays.
• rays are an indication of the direction of travel of the light; essentially
light is being modelled as a stream of particles.

5. Rays
An idealised point source of light
emits rays of light in all directions.
Intensity reduces with distance.
Very distant sources of light are considered to be sources of parallel rays. The
same goes for lasers.

6. A model - Waves

7. Reflection

8. Do you think the path would be
better modelled by rays or waves?
What do you notice about the symmetry of the
images? What law can you conclude?

9. Regular and diffuse reflection

10. Image Position
Object
Incident ray
Image

11. Image Position
You think in straight
lines!
The image is located
behind the mirror.

12. How far behind the mirror is your reflected
image?
Object
0.5 metres
Image
0.5 metres

13. Reflection, absorption and transmission
However, it is important to note that no
material is able to allow 100% of the incident
light to pass through. There are no perfectly
transparent materials; some reflection and
absorption of the incident light will always
occur.
A transparent material will allow a significant
amount of light to pass through it.
Most materials are opaque to visible light; that
is, they do not allow any light to pass through
them.

14. Summary