End-of-Year Revision


Light is a form of energy.
Light is created by stars but on Earth is produced in some chemical reactions (such as burning).
Light (usually) travels in straight lines. 
We can only see light when it enters our eye.
Al Hazen (about AD1000) showed that we see when light enters our eye - not because anything leaves our eyes.
When light strikes a surface it can either -
reflect (“bounce off” eg. a mirror or surface of water);
refract (enters a new substance and bends as it does so);
be absorbed (and turned into a heat energy).
Materials differ in the way they affect light.  They may be -
transparent (we can see clearly through them eg. most window glass) 
translucent light passes through them but we can’t see objects on the other side eg. most bathroom windows);
opaque (so that light cannot pass through them eg. metals, wood)
When light reflects, it obeys the law of reflection:

When a beam of white light shines on a prism, it is split into to a spectrum (“rainbow”).
The colours of the spectrum are - red, orange, yellow, green, blue, (indigo) violet (ROYGBV).
The primary colours for additive mixing are red, green and blue (as can be seen by looking at a computer screen with a magnifying glass). 
The structure of a mammal’s eye:

sclera - the tough white outer covering;
cornea - transparent front “window” of the eye which focusses the light on the retina;
lens - adjusts the for near or distant objects;
retina - where the image forms and where the sensory rods and cones detect light;
iris - adjust the size of the pupil, controlling how much light enters the eye.

Communication - means “sharing ideas”.
Communication may be between 2 people (personal communication) or large numbers of people (mass communication).
Communication involves the sender encoding the information and the receiver decoding the message.
Some codes include - 
English, German, Japanese and other spoken languages;
writing (in any language);
binary code (used in computers);
electrical signals in a wire or radio signal.
Communication technologies have revolutionised communication, including -
electric telegraph;