Light Waves Notes

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Light Waves Notes - PowerPoint PPT Presentation

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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Light Waves Notes

Laser

Part 1 – Properties of Light
• Light travels in straight lines:
• 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.

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
• 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 _________ angle it hits it.
• the same
• The same !!!
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
• Two examples:
• 1) A periscope
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
• 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 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
• 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

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

Homework

Some further examples:

blue

black

black

black

green

red

blue

black

Light & Colour Bill Nye

Red Filter

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

Red

• Blue
• Green
• White
• (All colors)

Primary Colours of Light

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

Secondary Colours of Light

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

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

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…
• This sound wave has a _____ frequency:
• high
• High pitch
• This sound wave has a ___ _frequency:
• low
• Low pitch
Drawing sounds…
• This sound wave has a _____ amplitude:
• high
• Loud
• This sound wave has a _____ amplitude:
• low
• Quiet

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