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Modelling Simple Light Properties
8.1 waves, particles, reflection, absorption, transmission
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.
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.
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.
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.
A model - Waves
Reflection
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?
Regular and diffuse reflection
Image Position
Object
Incident ray
Image
Image Position
You think in straight lines!
The image is located behind the mirror.
How far behind the mirror is your reflected image?
Object
0.5 metres
Image
0.5 metres
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.
Summary
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