There are two different types of waves, longitudinal and transverse. You need to know the differences between them (and how to spell them).
Transverse are the most common type of waves. For example: Light and other Electromagnetic (EM) waves and ripples on water.
In a transverse wave, the vibrations move at 90° from the direction of the wave.
Longitudinal waves are rarer. You can only find these as:
Where the wave is spread out is called rarefaction and where it's pushed together is called compression. See how these areas move in the animation.
A closer look...
When we draw out a wave, even if it's longitudinal, we always graph it as below:
You'll need to know what the following are: amplitude and wavelength.
It's very easy to make silly mistakes if asked to draw these, so study the following diagram:
Remember, take your time!
Reflection and Refraction
Both longitudinal and transverse waves can be reflected and refracted, but it's easier to see this in transverse.
Reflection of light is all around us. It's what allows us to see anything (fortunately the section of the eye has been cut from the exam). Basically, objects absorb certain lights, while they reflect others. It's these reflected lights that give objects their colour.
Black is in reality, not a colour at all. It absorbs all coloured light, and so we just see a void.
If light hits a rough surface, the reflected light bouces all over the place. This is called diffused reflection. (And here's a pretty picture for you):
Notice that the incoming light it straight, and all in the same direction. The Normal as you know, is the imaginary line that is at 90° from the surface. Because the surface is uneven, the light hits it at different angles, so bounces back at different angles.
When the light hits a smooth, shiny surface, like a mirror, you get a better reflection:
All the reflected rays are in the same direction, meaning a better reflection.
A closer look at reflection
Like, you know how we're all massively interested in watching waves in water? Did you know if a wave passes from deep water, to shallow water, the waves are actually bent?
For some reason the syllabus has an obsession with water waves... Anyway, this bending of waves is called refraction. It happens in both longitudinal and transverse waves. The beautiful Ripple Tank picture shows you it...
When we convert this to real physicals, the rule is: when a wave travels from dense to less dense water, the wave is slowed down. Only part of the wave's speed is changed at first, and this causes it to bend.
When a wave enters a denser medium, it is slowed down and bends towards the normal.
When a wave enters a less dense medium, it speeds up and is bent away from the normal.
And, to show this, here's the old refraction with light and a glass block:
Remember though: If the wave moves from one density to another along the normal (at 90°) there's no refraction. This is because all the wave is being slowed at the same time. There's still a change in wavelength.
Depending on the object, there can also be reflection.
When you did the old refraction with glass test, you might have noticed that some of the light was reflected back, out of it. This is called internal reflection and happens when light is exiting something dense like glass, water or perspex.
When you change the angle of the light on the block, the reflected light varies. At a certain angle, called the critical angle all the light is reflected, and none is refracted. When this happens we have total internal reflection.
How's total internal reflection used?
In glass, the critical angle is around 42° so we can make binoculars, periscopes, etc. Prisms give us a better image for binoculars than mirrors would:
Another use for optic fibres is in endoscopes. These have a lense system at each end. The optic fibres carry light down the endoscope, with is reflected from what you want to see, to the lense, and then back up. Endoscopes are used by doctors for looking inside people without chopping them up.
Ever wondered why you can hear someone talking around a corner? This is because waves spread out as they travel through something like a gap in a barrier. The wave has to "bend" to fit through the narrow gap, and this allows it to spread out. This spreading out is called diffusion. The next diagrams show how this works:
Naturally, diffraction depends on the wavelength. Small wavelengths are less likely to be affected by narrow gaps, because they'll fit through easily.
Large wavelengths, though, will be diffracted a lot, because they have to squeeze through everything.
If you live in the hills and you want to listen to the radio, you'll probably only be able to hear the long wavelength as it's easier for them to diffract over the hills, and to your house.
Sound and Ultrasound
Sound, as you know is one of the few longitudinal wave. We hear sound because of the vibration of particles. This is the main difference between light and sound - sound waves cannot travel through a vaccuum.
As with all waves, sound waves can be:
The bigger the amplitude of a wave, the louder the sound. The greater the frequency, the higher the pitch.
There is only a certain range of frequencies that the human ear can detect. Anything with a higher frequency than this range is called ultra sound. It can be produced by electronic systems and is useful in many different ways:
Light and Electromagnetic Waves