Welcome to Waves Day!
Objectives:
To learn about and begin to understand the following:
Observed waves:
- waves on water as undulations which travel through water with transverse motion; these waves can be reflected, and add or cancel – superposition.
Sound waves:
- frequencies of sound waves, measured in hertz (Hz); echoes, reflection and absorption of sound
- sound needs a medium to travel, the speed of sound in air, in water, in solids
- sound produced by vibrations of objects, in loud speakers, detected by their effects on microphone diaphragm and the ear drum; sound waves are longitudinal
- auditory range of humans and animals.
Energy and waves
- pressure waves transferring energy; use for cleaning and physiotherapy by ultra-sound; waves transferring information for conversion to electrical signals by microphone
Light waves
- the similarities and differences between light waves and waves in matter
- light waves travelling through a vacuum; speed of light
- the transmission of light through materials: absorption, diffuse scattering and specular reflection at a surface
- use of ray model to explain imaging in mirrors, the pinhole camera, the refraction of light and action of convex lens in focusing (qualitative); the human eye
- light transferring energy from source to absorber leading to chemical and electrical effects; photo-sensitive material in the retina and in cameras
- colours and the different frequencies of light, white light and prisms (qualitative only); differential colour effects in absorption and diffuse reflection.
Session One
Observed Waves
A Wave is a ridge or swell on the surface of a body of water, normally having a forward motion. The undulations and oscillations may be chaotic and random, or they may be regular, with an identifiable wavelength between adjacent crests and with a definite frequency of oscillation.
Ridge: A long narrow upper section or crest such as the ridge of a wave.
Crest or Peak: The top, as of a hill or wave.
Trough: A long, narrow depression, as between waves or ridges.
Swell: To increase in size or volume as a result of internal pressure; to expand.
Undulation: A regular rising and falling or movement to alternating sides; movement in waves.
Oscillation: A repetitive vibration with a regular frequency.
Wavelength: The distance between one peak of a wave to the next peak.
Frequency: The number of repetitions per unit time of a complete waveform.
Amplitude: The amplitude of an ocean wave is the maximum height of the wave crest about the level of calm water.
Try changing the frequency, amplitude, and wavelength here.
Activity One A
Label the parts of a wave form.
Activity One B
You will need:
Wooden skewers
Duct tape
Chewy candies
A glass of water
Session Two
What are sound waves?
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Sounds are produced by vibrations.
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Sound travels as waves, which are vibrating particles.
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Sound waves are reflected by surfaces.
How is sound produced?
When you bang a drum its skin vibrates. The harder you bang, the bigger the vibrations. The vibrating drum skin causes nearby air particles to vibrate, which in turn causes other nearby air particles to vibrate. These vibrating particles make up a sound wave.
Explore some sound activities here.
How does sound travel?
Sound waves travel at 343 m/s through the air and faster through liquids and solids. The waves transfer energy from the source of the sound, e.g. a drum, to its surroundings. Your ear detects sound waves when vibrating air particles cause your ear drum to vibrate. The bigger the vibrations the louder the sound.
Activity Two A
Sound on the Ear Drum
Carry out the activity here.
Reflection of sound
Surfaces reflect sound waves:
Hard surfaces reflect sound well, making echoes.
Soft surfaces, like curtains and carpets, reflect very little sound. They absorb the sound instead, so there are no echoes.
Activity Two B
Label the sound wave types
Activity Two C
Balloon Amplifier
You Need:
- A Balloon
To Do:
Blow up a balloon, hold it up, and tap on it. It doesn’t make a super loud sound. Next, hold the balloon up to your child’s ear and lightly tap on it. It sounds pretty loud!
Why does this happen? When you blow up a balloon you are packing it with air molecules. They are very close together and transmit sound waves super well compared to the air just around us normally.
When we tapped the balloon while we were just holding it those waves had to move through the less compressed ambient air to get to our ears, and the sound is softer.
When we hold the balloon up to our ears the sound just has to get through the tightly packed molecules in the balloon and we hear a louder sound. It is amplified.
Session Three
Light Waves
What is colour?
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The light that we see is made up of many different colours.
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There are three primary colours: red, green and blue. They can be combined in different ways to make every other colour.
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The colour of an object is determined by the wavelength of light that it reflects.
Activity Three A
Make More Colors.
You will need:
- laminator and pockets
- colored cellophane
- scissors
- key rings or string
- hole punch
You need to make something like these (but only with the three primary colors of science – red, green and blue):
Additive Colours
Additive colours are colours that are associated with emitted light directly from a source before an object reflects the light. These colours are red, green and blue. These are the colours we are probably most familiar with in association with television, and computer displays. The additive colour theory, was first described by James Clark Maxwell in the mid 1800s. When equal amounts of Red Green and Blue light are combined, they produce white light. By adding the colours together to produce white, we call these additive colours.
Red, green and blue are the “primary” colours of white light. The combination of all three of these colours will result in white. This is called Colour by addition and is direct way to prove that all of these three colours do indeed come from white light.
Activity Three B
Understanding additive colours
The three colour torches above show how when red green and blue are mixed, other colours are produced… including white! This is called colour by addition.
A simple way to understand a little more about additive colours is to create some of your own using torches or ‘flashlights’ with coloured filters attached.
The three colour torches show how when red green and blue are mixed, other colours are produced… including white! This is called colour by addition.
You will need:
Three similar torches (preferably identical ) Light filters or similar to cover the torch heads elastic bands (to hold the colour filters in place) A white surface to shine your torches
Step 1.
Cover the front of each torch with a colour filter – one torch with a Blue light filter one with a Green light filter, and the other with a Red light filter. Use the elastic bands to hold them in place.
Step 2.
Arrange the torches so that the beams of light just overlap each other on the white surface. You may need to enroll a friend to help you do this! You could also use three photographic tripods if you access to them… and tape the torches to them.
For the best results, use a white wall or surface to shine the torches on. The effect is also best achieved in a dark room.
Step 3.
If you have the torches arranged correctly, the result is that in the middle of the three light beams, the area is white. It may take a while to arranged the torches correctly, but once they are, you should see that in the middle where all three colours meet the are is white.
You will also see other colours that have been produced. These should be Magenta, Yellow, and Cyan (another bluish colour) These are called secondary colours.
What are light and colour?
White light from the Sun is a mixture of colours, each with a different frequency. You can use a prism to split (or disperse) white light into a spectrum of colours: red, orange, yellow, green, blue, indigo and violet. Dispersed means that the colours are separated out.
We see higher frequencies of light as blue or violet, lower frequencies of light are seen as red and orange. Green light is in the middle.
A prism is any object that separates white light into the colors of the rainbow — red, orange, yellow, green, blue, indigo, and violet. It works by refracting light, and breaking it according to its wavelength. You can purchase a triangular prism of glass or plastic from hobby stores, and you can also make a prism from a simple glass of water.
Activity Three C
Split light
You will need:
- A glass
- Water
- A light source (flashlight, phone)
- White paper
Fill the glass with water so that it’s slightly more than half full. Place the glass on the edge of a coffee table or other flat surface, so that almost half of the glass’s bottom hangs over the edge. Be careful that the glass does not fall over the edge.
Place the two sheets of paper side by side on the floor next to the coffee table. Turn the flashlight on and point it toward the glass so that the light goes through the glass and onto the sheets of paper on the floor.
Adjust the position of the flashlight and the paper until you can see the characteristic rainbow on the sheets of paper. This may require a trial and error to get the angles just right. You may also get more than one rainbow.
Who needs to know about light and colour?
Light and colour are fundamental for photography. An object can have different coloured lights shone on it to bring out certain features.
Activity Three B
Additive Primary Colours
What are light waves?
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Light travels in waves.
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Light waves travel in straight lines.
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Light waves travel faster than sound waves.
How does light move?
Light travels as waves. Light waves don’t always need particles to travel through. They can also travel through outer space or a vacuum.
Light waves travel in straight lines. You can detect them with your eyes, and also with instruments such as cameras. They are reflected by mirrors and change direction when they travel from the air into glass or water.
Light travels very fast. It has a speed of 300 million metres per second in a vacuum. It only takes 8 minutes and 20 seconds for light to travel from the Sun to the Earth. Light travels through the air about a million times faster than through sound, which explains why you see lightning before you hear thunder.
Watch this – An oldie but a goodie!
Session Four
Wrap Up!
Waves Quiz.
Waves
A brief introduction to observable, light, and sound waves, discussing wave velocity, frequency, and wavelength
