Properties Of Waves
There are two types of Wave:
- A Transverse Wave is where the oscillations are Perpendicular to the direction of energy transfer, e.g electromagnetic waves are water waves.
- A Longitudinal Wave is where the oscillations are Parallel to the direction of energy transfer, e.g sound waves. These waves show areas of compression and rarefraction.
All waves transfer energy. Mechanical waves (e.g. water waves, waves on springs and shock waves) may be transverse or longitudinal.
The electronmagnetic spectrum extends from high frequency or high energy (short wavelength 10-15m) waves, e.g gamma rays, to low frequency or low energy (long wavelength 10+4m) waves e.g radio waves.
Visable light is only one type of electromagnetic raditation and is the only part of the electromagnetic spectrum that can be seen with the eye. It consists of severn coulors from red to violet.
- Radio Waves Long Wavelength , Low Frequency
- Microwaves |
- Infrared rays |
- Visable Light |
- Ultraviolet Rays |
- X-rays V
- Gamma Rays Short Wavelength , High Frequency
The Amplitude of an electromagnetic waves is the peak movement of the wave from it's rest point.
The frequency of an electomagntic wave is the number of waves passing in one second .Frequency is measured in Hertz (Hz)
The connection between frequency and wavelength is given by the wave equation.
v= f x (wavelength)
When a wave strikes a relective surface it changes direction this is called, reflection.
The normal line is the construction line drawn perpendicular to the reflecting surface at the point of incidence. The normal line is used to calculate the angles of incidence and reflection.
When an object is viewed in a plane mirror the image formed is ...
- Virtual (i.e on the opposite side of the mirror)
- Upright (i.e in the same orientation)
- The Same Size as the object
- Laterally Inverted (i.e left become right)
Sound travels as a wave. These are called longitudinal waves beacuse they cause vibrations (backwards and forwards) within a material (medium). Sound waves can't travel through a vacuum.
The frequency of a sound wave is the number of vibrations produced every second, i.e hertz (Hz). Humans can hear sounds in the range of between 20Hz and 20,000Hz.
The pitch of a sound is determined by it's frequency. As the frequency increases the pitch becomes higher.
Echos are examples of sound being reflected at a surface.
If a wave source is moving away from, or towards, an observer there will be a change in the :
- observed wavelength
- observed frequency
The model that's used to describe this phenomenon is known as the Doppler effect. An ambulance racing past you is a good example of the Doppler effect with sound waves.
- When a light source moves away from you the observed wavelength increases and the frequency decreases.. This is known as red-shift.
- When a light source moves towards you the observed wavelength decreases and the frequency increases. This is known as blue-shift.
The light observed from distant galaxies in the universe is red-shifted. In fact the further away a galaxy is, the faster it is moving and the bigger the observed increase in wavelength.
The Big Bang and CMBR
The Big Bang
The observed red-shift of galaxies supports the idea that the....
- the whole Universe is expanding
- the expansion began from a very small initial point in a huge explosion known as the Big Bang.
Cosmic Mircowave Background Raditation (CMBR)
CMBR is a form of electromagnetic radition that fills the entire Universe. It comes from radition that was arounf shortly after the beginning of the Universe but which has now been Stretched.
The Big Bang thory is currently the only theory that can explain the exsistence of CMBR.