KS3+Light

Use light travelling in a straight line to explain the formation of shadows and other phenomena

**Light**
Ray : The paths along which light energy travels. A beam of light is a bundle of light rays. Light rays are represented by straight lines with arrows to show their direction of motion.

3. Types of light : Sun or Moon
=> Does it produce light or reflect light? (Luminous / Non Luminous)

Light travels straight line. Light travels without any medium.
[|Shadow of light]

We are able to see only the colours that bounce back from an object to our eyes.
media type="custom" key="27955799"

Investigate how a pin-hole camera works [|The pinhole camera]

Describe reflection at a plane surface and use the law of reflection

**Reflection:**
[|What happens when light hits a plane mirror?] __R eflection __: Light bounces off on the surface of an object.

**Refraction:**
[|What happens when light travels through a glass block?] __R efraction __: Light changes its direction when it passes from one medium to another.

[|Image from gcsescience.com]

The incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane.

 * Critical angle**: A special angle of __ incidence __ where the angle of refraction in the less dense medium is __ 90 __ degree.





Explain the dispersion of white light. [|What happens when light passes through a prism?] [|What happens when the spectrum passes through a prism?] Prism

**Rainbow**
Pure sunlight is made up of seven colours mixed up together to form 'white light'. You can 'unmix' them by passing a beam of sunlight through a drop of water. The beam of sunlight bends or refracts inside the drop and sort of bounces around or reflects inside too. When the beam leaves the drop, it is off-colour, so to speak. Each colour has been bent a little differently. The result is no longer white light but a rainbow.

A beam of light going through a raindrop is bent going through the first surface. Then it bounces off or is reflected from the back surface. Finally it leaves the first surface again. It has lost some of its intensity and is travelling at an angle to its original incoming direction. Red light leaves at 42 degree to its original direction, violet at 40 degree and every other colour at an angle in between. Therefore all the seven colours are spread over there 2 degree. We can see this when the sun is shining from behind us and only because the droplets of water in the air are perfect spheres. The "teardrop" shape of water is only found when it is about to fall off.

On a bright sunny day, you can make your own small rainbow with a garden hose. Turn on the water for a powerful flow. Place your thumb over the end of the hose to scatter the water into thousands of tiny drops. As the drops fall through the air, they act like rain and make a rainbow. To see the rainbow, you must stand with your back to the sun. The "rainbow" is in fact a 'rain-circle'. You can only see part of it from the ground. People in an airplane can see the whole circle.

Explain colour addition and subtraction, and the absorption and reflection of coloured light. [|What happens when primary color of light combines?] [|What colors will the clothes be in each colored light?]

Resources from http://springfield.uk.net [|Light and colour from Youku] [|Light optics from Youku] Investigate/research the electromagnetic spectrum ( uv light, infra red, gamma, x yas and radio waves) [|What are the properties of the electromagnetic spectrum?] Why is the sky blue? from youtube.com media type="custom" key="27936963" Why is the sky blue not violet? media type="custom" key="27937333" * ELECTROMAGNETIC SPECTRUM * Images from www.epa.gov and [|staff.norman.k12.ok.us]

[|How pinhole camera works] from schoolphysics.co.uk

For fun Is your red the same as my red? Vsauce from youtube.com media type="youtube" key="evQsOFQju08" width="504" height="283"

Try this Colours from notonefoot youtube.com Optical illusion 1 colour from black and white media type="youtube" key="MUbraNFEHkA" width="504" height="377" Brain Games colour illusion from Brain Games youtube.com media type="youtube" key="QnQg2ij5wM8" width="504" height="283"

Describing colours as a blind person from TommyEdisonXP youtube.com media type="youtube" key="59YN8_lg6-U" width="504" height="283"

10 optical illusions that will melt your mind from Matthew Santoro youtube.com media type="youtube" key="izNIN9eu5ck" width="504" height="283"

Brain Games Misconceptions from Kate Hasbourg youtube.com media type="youtube" key="jJiYHLVWNDE" width="504" height="283"