Unit 3 – Light and Optic Systems
Topic 1 – What Is Light?
Light: is a form of energy that you can see
The sun is a natural light source.
Light bulbs are an example of an artificial light source
Radiate: to send out energy in the form of waves or rays.
Light can be produced by converting different kinds of energy- electric, chemical, fusion, heat etc. Light energy can also be transformed to different types of energy.
Incandescent Sources
An object can be heated to such a high temperature that it emits visible light, Incandescent source.
Incandescent lights give off about 95% of the energy as heat and the other 5% as light.
Fluorescent Sources
Materials absorb high-energy ultraviolet light and later emit some of this energy known as fluorescence.
This is the same process that takes place in a fluorescent bulb. See Figure 3.6 on pg 181
The advantage over incandescent lights is less energy is wasted as heated. However they are more expensive to produce.
Phosphorescent Sources: stores up energy and emits light even after the energy source has been taken away. eg. glow in the dark stars in your bedroom.
Chemiluminescent Sources: light can also be released by chemical reactions e.g. Glow sticks.
Bioluminescent Sources: Living creatures that produce their own light through chemical energy within your bodies.
Luminous: objects that emit light.
Non-luminous: do not emit light.
The Ray Model of Light
Ray: a straight line that represents the path of a beam of light.
Transparent: Allowing light to pass through e.g. Water, air, and glass.
Translucent: materials that allow some light to pass through, the light is scattered from its straight path. E.g. Some types of glass and plastic.
Opaque: a material that totally blocks light
Topic 2 – Reflection
Reflection: a process by which light strikes a surface and bounces back off that surface.
Incidents Ray: The ray that comes from the light source and strikes the surface.
Reflected Ray: The ray that bounces off the surface.
Normal Line: When a ray strikes the surface perpendicular (at a 90 degree angle)
Angle of Incidence: the angle between the incidence ray and the normal line
Angle of Reflection: the angle between the normal line and the reflected ray.
Law of Reflection: the angle of incidence equals the angle of reflection.
Convex: mirror bulges outward – like a party balloon
Concave: curved inward - like a bowl
Topic 3 – Refraction
Refraction: the bending of light when it travels from one medium to another.
Angle of refraction: the angle between the normal and the refracted ray.
*Know Table 3.1 on Page 205
Topic 4 – Lenses and Vision
Concave Lens: causes the refracting rays to spread apart.
Convex Lens: causes the refracting rays to come together.
The lens of the human eye is a convex lens.
Focus: bringing light rays to a point.
Retina: A light sensitive area at the back of the eye.
Near sighted: means that you have trouble seeing distant objects.
FarSighted: the opposite of near sighted
*See figures 3.32 on page 210
* Know the parts of the eye diagram on pg 211
The shortest distance at which an object is in focus is called the near point (Humans: Adults; 25cm, Babies; 7 cm)
The longest distance is the far point, which is said to be infinity.
Diaphragm: controls the amount of light that gets in by controlling the size of the aperture (opening)
Shutter: controls how much light enters by staying open a long or short amount of time.
Iris: in the human eye is the colored ring that functions like a diaphragm.
Pupil: size of the opening that is controlled by the iris. (Dark part of the eye)
Iris Reflex: the iris adjusts the size of your pupil to meet the extreme dark or light, very rapid (try this in the bathroom mirror)
Optic nerve: sends information about what is seen by the eye to the brain.
Blind Spot: at the point where the optic nerve attaches to the retina does not have any light sensing cells therefore you can’t see that area.
*Know diagram on page 218 figure 3.38