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Light Waves Notes. 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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part 1 properties of light

Laser

Part 1 – Properties of Light
  • Light travels in straight lines:
slide3
Light travels VERY FAST – around 300,000 kilometres per second.
  • At this speed it can go around the world 8 times in one second.
slide4

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.
slide6

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

Sun

Stars

Light Bulb (when on)

Firefly

Mirror

Moon

Person

Desk

Paper

part 2 reflection
Part 2 - Reflection
  • Normal
  • Reflection from a mirror:
  • Reflected ray
  • Incident ray
  • Angle of reflection
  • Angle of incidence
  • Mirror
slide8

Angle of incidence = Angle of reflection

  • The Law of Reflection
  • In other words, light gets reflected from a surface at _________ angle it hits it.
  • the same
  • The same !!!
clear vs diffuse reflection
Clear vs. Diffuse Reflection
  • Smooth, shiny surfaces have a _____ reflection:

Clear

  • Rough, dull surfaces have a ______ reflection.
  • Diffuse reflection is when light is scattered in different directions

Diffuse

using mirrors
Using mirrors
  • Two examples:
  • 2) A car headlight
  • 1) A periscope
colour
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
The colours of the rainbow:
  • Red
  • Orange
  • Yellow
  • Green
  • Blue
  • Indigo
  • Violet
adding colours
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
seeing colour

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
slide15

A pair of purple trousers would reflect purple light (and 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
Using coloured light
  • If we look at a coloured object in coloured light we see something different. For example, consider a football kit:
  • Shirt looks red
  • White
  • light
  • Shorts look blue
slide17

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
some further examples

Homework

Some further examples:

blue

black

black

black

green

red

blue

black

light colour bill nye
Light & Colour Bill Nye
  • http://www.youtube.com/watch?v=gtgBHsSzCPE
using filters

Red Filter

  • Magenta Filter
Using filters
  • Filters can be used to “block” out different colours of light:
investigating filters
Investigating filters
  • red
  • green
  • blue
  • Blue, green, cyan
  • Red, blue, magenta
  • Red, green, yellow
slide22

Red

  • Blue
  • Green
  • White
  • (All colors)

Primary Colours of Light

  • Black
  • Yellow
  • Cyan
  • Magenta
  • (No Color)

Secondary Colours of Light

refraction
Refraction
  • Speed up
  • Refraction is when waves _______ or slow down due to travelling in a different _________. A medium is the area or space that waves will travel through.
  • For example, if you put a pen in a cup of water, the light rays are slowed down by the water and are _____, causing the pen to look odd.
  • ~Two examples on next slide~
  • medium
  • bent
slide24

Due to change in medium, the phase velocity of the wave is changed but its frequency remains constant (the same).

sound the basics
Sound – The basics
  • vibrate
  • We hear things when they ________.
  • If something vibrates with a ____________
  • (vibrates very ______) we say it has a _____ pitch.
  • If something vibrates with a ___________ (vibrates ______) we say it has a ____ pitch.
  • High frequency
  • fast
  • high
  • Low frequency
  • low
  • slow
drawing sounds
Drawing sounds…
  • This sound wave has a _____ frequency:
  • high
  • High pitch
  • This sound wave has a ___ _frequency:
  • low
  • Low pitch
drawing sounds1
Drawing sounds…
  • This sound wave has a _____ amplitude:
  • high
  • Loud
  • This sound wave has a _____ amplitude:
  • low
  • Quiet
slide28

Conclusion:

  • The pitchor note of a sound that we hear is determined by its wavelength or its frequency.
  • The shorter the wavelength, the higher the frequency becomes, and the higher the pitch that we hear.
  • The amplitude of a sound wave is the same thing as loudness.
    • The wavelength of a wave is independent of its amplitude [loudness] and inversely proportional to its frequency.

Independent— wavelength does not affect loudness.

Inversely proportional—high frequency = short wavelength,

low frequency = long wavelength