Light always travels in straight lines.
Light travels much faster than sound. Light travels at 300 000 km per second , in air sound travels at about 330 m per second. This is why events can be seen before sound from them can be heard. Light is a form of radiation and it can travel through space (a vacuum ).
Shadows are places where the light doesn’t shine. They are formed because light travels in straight lines. If light could travel in curved lines or around corners then it would get behind opaque objects and shadows would not be formed.
Opaque means not see-through, transparent means see- through.
Light is produced by luminous objects, such as Sun, candles, flame, light bulbs or glow worms.
Light reflects off non-luminous objects, in other words everything else, e.g. Moon, planets, people, animals etc.
Light reflects off these objects and goes into our eyes and that is how we see.
Almost all non-luminous objects reflect some of the light that falls on them. Most of these objects scatter light. That is, they reflect light in all directions.
Reflection
Mirrors have a very smooth shiny surface which reflects all the light off at the same angle as the light strikes the surface.
So they reflect light in a regular and predictable way.
This can be described by the law of reflection: the angle of incidence (i) = the angle of reflection (r)
The ray of light striking the mirror is called the incident ray.
The ray of light leaving the mirror is called the reflected ray.
The vertical line is called the normal . This is a line at right angle to the surface of the mirror where the light strikes the mirror.
Rough, uneven surfaces look dull because the light is reflected back in lots of different directions.

Refraction
Refraction happens when light rays move to a more or less dense substance.
As light passes from one transparent material to another, its speed changes slightly.
Light slows down when it passes from air into glass or water. It speeds up when passes out of those materials into air.
When the light passes into and out of these materials at right angles to the surface then the ray passes through with no change of direction.
If the light passes into or out of a material at an angle it will change the direction as it crosses the boundary between the two materials.
When the light is slowed down, its direction moves towards the normal line.
When the light speeds up, its direction moves away from the normal line.
The process is called refraction.
Colours
White light is a mixture of colours . When white light hits a prism or a rain drop it gets dispersed and splits up into a full rainbow of colours. The proper name of this rainbow is a spectrum . The spectrum of white light contains seven colours- red, orange, yellow, green, blue, indigo and violet.
Coloured filters are translucent – they only allow specific colour of light to pass through them. A red filter will allow red light to pass through but i will absorb all of the other colours of the spectrum. The only colour that can be seen leaving a red filter is red.
Coloured objects appear different when illuminated by different colours of light. When a green ball is illuminated with white light it reflects the green light and absorbs all the other colours. When a green ball is illuminated by red light, there is no green light to reflect. So, the green ball will appear black because it only absorbs the red light.
White objects reflect all colours.
Black objects absorb all colours.

Vocabulary absorb – pochłaniać allow pozwolić angle – kąt angle of incedence – kąt padania angle of reflection – kąt odbicia away from – dalej od boundary – granica dense – gęsty direction – kierunek dispersed – rozszczepiony dull – matowy filter – filtr illuminated - oświetlone luminous – świecący mixture – mieszanina opaque – nieprzezroczysty pass – przejść prism – pryzmat ray – promień (np. światła) reflect- odbijać (światło) reflect off – odbijać się reflection - odbicie refraction – załamanie (światła) right angle – kąt prosty rough – nierówna scatter – rozpraszać shadow – cień spectrum – widmo straight – prosty surface – powierzchnia towards – w stronę transparent, translucent – przezroczysty vacuum – próżnia
Tasks
1.
How many times is light faster than sound?
2.
What is a luminous object? Give 3 examples.
3.
Name three things that reflect light.
4.
How could you make a shadow of an object bigger?
5.
What is the name of a line drawn at right angle to the surface of a plane mirror?
6.
What is the law of reflection?
7.
What happens to the speed of light as it passes from air into water?
8.
Complete:
Light .......................................direction as it passes from ................................ material to another.
9.
Which colour of white light is refracted most as it passes through a glass prism?
10.
What is the only colour of light that can be seen leaving a blue filter?
11.
Peter used white light from a spotlight and put a red and a green filter in front of it. a) No light reached the screen. Explain why? b) Peter cut a circular hole in the green filter. Describe what Peter would see on the screen.
12.
What happens to all the colours in white light when they hit a black object?