2 Part 1 – Properties of Light Light travels in straight lines:Laser
3 Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.
4 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.
5 We see things because they reflect light into our eyes: Homework
6 Luminous and non-luminous objects A luminous object is one that produces light.A non-luminous object is one that reflects light.Luminous objectsReflectors-The Sun- Lamps- Lights- Lasers- CampfiresThe MoonMirrorsPeopleObjects
7 ShadowsShadows are places where light is “blocked”:Rays of light
8 Out of the DarknessIf the light source is small compared to the size of the object, then the shadow will be SHARPIf 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.
9 Properties of Light summary Light travels in straight linesLight travels much faster than soundWe see things because they reflect light into our eyesShadows are formed when light is blocked by an object
10 Part 2 - Reflection Reflection from a mirror: Mirror Normal Incident rayReflected rayAngle of incidenceAngle of reflectionMirror
11 Angle of incidence = Angle of reflection The Law of ReflectionAngle of incidence = Angle of reflectionIn other words, light gets reflected from a surface at THE SAME ANGLE it hits it.The same !!!
12 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
13 Using mirrorsTwo examples:2) A car headlight1) A periscope
14 Flat MirrorsImage is VIRTUAL, UPRIGHT, UNMAGNIFIED
15 Spherical Mirrors - Concave FImage is REAL, INVERTED, and DEMAGNIFIED !!!
16 Spherical Mirrors – Concave Object Inside the Focal Point Image is VIRTUAL, UPRIGHT, and MAGNIFIED
17 Spherical Mirrors - Convex FImage is VIRTUAL, UPRIGHT, and DEMAGNIFIED
18 ColourWhite 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.
19 The colours of the rainbow: RedOrangeYellowGreenBlueIndigoVioletRemember: Roy G. Biv !!!
20 Light from the SunThe 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!
21 Wavelengths of Light Red Light – l = 680 nm Green Light - l = 500 nm Blue Light - l = 470 nm
22 Adding coloursWhite 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 yellowAdding all three makes white again
23 Only red light is reflected Seeing colourThe colour an object appears depends on the colours of light it reflects.For example, a red book only reflects red light:HomeworkWhitelightOnly red light is reflected
24 (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 lightA white hat would reflect all seven colours:Whitelight
25 Using coloured lightIf 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 redWhitelightShorts look blue
26 In different colours of light this kit would look different: RedlightShirt looks redShorts look blackShirt looks blackBluelightShorts look blue
27 Using filters Red Filter Filters can be used to “block” out different colours of light:Red FilterMagenta Filter