Light Properties of light Reflection Colours

Part 1 – Properties of Light Light travels in straight lines: Laser

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 -The Sun - Lamps - Lights - Lasers - Campfires The Moon Mirrors People Objects

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

Out of the Darkness If the light source is small compared to the size of the object, then the shadow will be SHARP If the light source is of comparable size to the object, then the shadow will be “fuzzy”. The dark inner region is called the UMBRA; the grey region is called the PENUMBRA.

Properties of Light summary 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 2 - 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 THE SAME 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

Flat Mirrors Image is VIRTUAL, UPRIGHT, UNMAGNIFIED

Spherical Mirrors - Concave F Image is REAL, INVERTED, and DEMAGNIFIED !!!

Spherical Mirrors – Concave Object Inside the Focal Point Image is VIRTUAL, UPRIGHT, and MAGNIFIED

Spherical Mirrors - Convex F Image is VIRTUAL, UPRIGHT, and DEMAGNIFIED

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

The colours of the rainbow: Red Orange Yellow Green Blue Indigo Violet Remember: Roy G. Biv !!!

Light from the Sun The light from the sun contains a grand mixture of electromagnetic waves of varying frequency (i.e. wavelength) The spectrum of light is characteristic of the TEMPERATURE of the sun!

Wavelengths of Light Red Light – l = 680 nm Green Light - l = 500 nm Blue Light - l = 470 nm

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

(or red and blue, as purple is made up of red and blue): A pair of purple pants, in addition to being ugly, would reflect purple light (or red and blue, as purple is made up of red and blue): Purple light A white hat would reflect all seven colours: White light

Using coloured light If we look at a coloured object in coloured light we see something different. For example, consider the outfit below – I mean, from a physics standpoint, not as a fashion choice: Shirt looks red White light Shorts look blue

In different colours of light this kit would look different: Red light Shirt looks red Shorts look black Shirt looks black Blue light Shorts look blue

Using filters Red Filter Filters can be used to “block” out different colours of light: Red Filter Magenta Filter