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Light. Properties of light Reflection Colours. Laser. Part 1 – Properties of Light. Light travels 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.
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Light • Properties of light • Reflection • Colours
Laser Part 1 – Properties of Light • Light travels 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.
Thunder and lightning start at the same time, but we will see the lightning first. • Light travels much faster than sound. For example: • 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
A luminous object is one that produces light. A non-luminous object is one that reflects light. • Luminous and non-luminous objects Luminous objects Reflectors • The Moon • Mirrors • People • Objects -The Sun - Lamps - Lights - Lasers - Campfires
Rays of light Shadows are places where light is “blocked”: • Shadows
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 Normal • Reflection from a mirror: Reflected ray Incident ray Angle of reflection Angle of incidence Mirror
Angle of incidence = Angle of reflection • The Law 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 • Image is REAL, INVERTED, and DEMAGNIFIED !!! C F
Spherical Mirrors – ConcaveObject Inside the Focal Point • Image is VIRTUAL, UPRIGHT, and MAGNIFIED F C
Spherical Mirrors - Convex • Image is VIRTUAL, UPRIGHT, and DEMAGNIFIED C F
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
Homework Seeing colour • The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected
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
Red light Shirt looks red • In different colours of light this kit would look different: Shorts look black Shirt looks black Blue light Shorts look blue
Red Filter Magenta Filter Using filters • Filters can be used to “block” out different colours of light: