Waves and Radiation

Vibrations in same direction as the wave transfers energy
Rarefractions are when the vibrations are spread out
Compressions are when the vibrations are close together

Most waves are transverse
The vibrations are at 90 degrees (perpendicular) to the direction energy is travelling by the wave

Distance from the equilibrium position to the maximum displacement (height of the wave)

A line joining points on a wave at the same point in their wave cycle at a given time

The number of waves that pass a single per second (measured in Hertz- 1Hz is one wave per second)

The time taken (in seconds) for one complete wave to pass a fixed point

The distance between a point on one wave and the same point on the next wave

They transfer energy and information without transferring matter

frequency x wavelength

f x (lambda)

1/ time period

1/t

If a wave source is moving relative to an observer, the Doppler Effect will occur. The Doppler Effect is the apparent change in frequency of a wave caused by the relative motion of the source of the wave and the observer.
If the motion relative to the source is towards then the frequency of a wave will be higher and the wavelength will be shorter as the wavefronts will be close together
If the motion is away from the source then the frequency of a wave will be lower and the wavelength will be longer as the wavefronts will be spread out

Wavelength is between 1m and (10 to the power of 4)m
No dangers
Used for communication (TV and radio broadcasting) and sonar

Wavelength is (10 to the power of -2)m
Heating of water in tissue can cause burning
Used for satellite communication

Wavelength is (10 to the power of -5)m
Causes burning of tissue
Used for thermal imaging and remote controls as well as to cook food (in a grill)

Wavelength is (10 to the power of -7)m
Activates sensitive cells in retina
Used for seeing and optical fibre communication

Wavelength is (10 to the power of -8)m
Can damage surface cells and cause blindness
Some frequencies can cause cell mutation and cancer
Used for fluorescent lighting

Wavelength is (10 to the power of -10)m
High doses can kill living cells
Lower doses can cause cell mutation and cancer
Used for creating images of inside the body and for studying the atomic structure of materials

Wavelength is (10 to the power of -12)m
High doses can kill living cells
Lower doses can cause cell mutation and cancer
Used to sterilise food and medical equipment as well as for treating tumours

angle of incidence = angle of reflection

Formed when the light rays bouncing off an object onto a mirror are diverging so the light from the object appears to be coming from a completely different place

sin(i) / sin(r)

1/n

When a wave crosses a boundary between two substances (of different densities), it changes speed
EM waves travel slower in denser substances
Sound waves travel faster in denser substances
If the wave hits the boundary 'face on', it will slow down/speed up but will carry on in the same direction
If the wave meets the different medium at an angle, it will slow down/speed up and will change direction

The refractive index of a transparent material tells you how fast light travels in that material
Refractive index of glass is high (around 1.5) so light slows down a lot in glass
Refractive index of water is around 1.33
Refractive index of air is about the same as in a vacuum so around 1.00 (so light travels quickly through air)

When the angle of incidence is greater than the critical angle, so all the light is reflected inside the denser medium
Allows us to use prisms to see objects that are not in our direct line of sight as the ray of light travels into one prism where it is totally internally reflected by 90 degrees, travelling to another prism lower down where it is totally internally reflected by 90 degrees again so the ray is now travelling parallel to its initial path but at a different height
Optical fibres made of plastic or glass consist of a central core surrounded by cladding with a lower refractive index and the core is so narrow that light signals passing through it always hit the core-cladding at angles higher than the critical angle so the light is always totally internally reflected

The angle between the normal and the incident ray
The incident angle when the refracted angle is equal to 90 degrees

20Hz to 20,000Hz

Longitudinal waves caused by vibrating objects
Because sound waves are caused by vibrating particles, the denser the medium, the faster sound travels through it
Sound cannot travel through a vacuum as there are no particles
They travel faster in solids than in liquids and gases
Reflected by hard, flat surfaces
Soft surfaces (like carpets and curtains) will absorb them

Displays sound waves
The greater the amplitude of a sound wave, the more energy it carries so it will be louder
The higher the frequency (the more complete wave cycles on the screen), the higher the pitch

Use two microphones, signal generator, oscilloscope and speaker
Start with both microphones next to speaker then slowly move one away until the two waves are aligned on the display but exactly one wavelength apart
Measure distance between microphones to find the wavelength
Use the formula 'speed= frequency x wavelength' to find the speed

Different wavelengths of light refract by different amounts so white light (which is a mixture of all visible frequencies) disperses into different colours as it enters a prism and the different wavelengths are refracted by different amounts, the same effect happening as light leaves the prism, creating a rainbow effect