Light

Light In this unit: Light is form of energy Properties of light Reflection Colours Refraction

Keywords

Light is form of energy Light can do work eg. Crookes radiometer Light can be converted to other forms of energy e.g. Solar cell, light to electricity. Other forms of energy can be converted to light e.g. Fire.

Part 2 – Properties of Light Light travels in straight lines: Laser The occurance of what is due to light traveling in straight lines?

Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.

Light travels much faster than sound. For example: Thunder and lightning start at the same time, but we will see the lightning first. 2) When a starting pistol is fired we see the smoke first and then hear the bang.

We see things because they reflect light into our eyes: Homework

Luminous and non-luminous objects A luminous object is one that produces light. A non-luminous object is one that reflects light. Luminous objects Reflectors

Shadows Shadows are places where light is “blocked”: Rays of light

shadows A solar eclipse is a spectacular shadow caused when the moon passes between the sun and the earth. Part of the earth goes completely dark.

Properties of Light summary Light is a form of energy Light travels in straight lines Light travels much faster than sound We see things because they reflect light into our eyes Shadows are formed when light is blocked by an object

Part 3 - Reflection Reflection from a mirror: Mirror Normal Incident ray Reflected ray Angle of incidence Angle of reflection Mirror

Angle of incidence = Angle of reflection The Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at ____ _____ angle it hits it. The same !!!

Clear vs. Diffuse Reflection Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

Using mirrors Two examples: 2) A car headlight 1) A periscope

Uses of Reflection Periscope Shaving/make-up mirrors Moving mirrors in lighthouses Security mirrors in stores, trains and buses. Reflectors on bicycles, on the road etc. Mirrors to direct the light in microscopes.

Colour White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow. Scientists call this a spectrum We can demonstrate this by splitting white light with a prism: This is called dispersion This is how rainbows are formed: sunlight is “split up” by raindrops.

The colours of the rainbow: Red Orange Yellow Green Blue Indigo Violet

Adding colours White light can be split up to make separate colours. These colours can be added together again. The primary colours of light are red, blue and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding red and green makes yellow Adding all three makes white again

Only red light is reflected Seeing colour The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: Homework White light Only red light is reflected

Refraction Refraction is the bending of light as it passes from one medium to another. Here the pencil looks like it is broken due the refraction.

Refraction through a glass block

Lenses A lens is a piece of glass or other transparent material that has at least one curved surface. Two types 1. Converging (convex) lens, brings the light rays closer together.

2. Diverging (concave) lens, spreads the light rays apart.

2. Diverging (concave) lens, spreads the light rays apart.

Uses of Refraction Lens in cameras, telescopes, microscopes and glasses. Phorensic analysis of crime evidence. Colours seen in diamonds or a rainbow. Extra daylight due refraction of sunlight in our atmosphere.