Waves Flashcards
what are the two types of waves
mechanical and electromagnetic
what is an example of a transverse wave?
the ripples on a water surface
longitudinal waves show areas of what?
compression and rarefraction
what type of waves are sound waves travelling through the air.
longitudinal
what is the difference between transverse and longitudinal waves?
In longitudinal waves , the vibrations are parallel to the direction of wave travel.
In transverse waves , the vibrations are at right angles to the direction of wave travel.
Waves transfer energy without transferring ……………..
Waves transfer energy without transferring matter.
Some waves need to travel through a substance, for example……….or…………
for example air or water.
what happens when waves travel through a substance
As the wave passes the particles of the substance are disturbed and oscillate (move back and forth).
Once the wave has passed, the particles return to their original positions.
Mechanical waves:
sound, water, seismic, waves on springs or ropes
travel through a medium (or substance) that oscillates
An example of energy transfer by mechanical working
Electromagnetic waves:
Radio, microwave, IR, light, UV, X Ray, Gamma Ray
These are oscillations in magnetic and electric fields
They do not need a substance.
They can travel through a vacuum, like space.
Responsible for heating by radiation
Mechanical waves can travel in two ways:
Longitudinal waves
Transverse waves
Wavelength:
This is the distance from a point on one wave to the same point on the next wave. It is measured in metres and has the symbol λ (Greek letter lambda)
Amplitude:
the height of the wave from the rest position to a peak or trough. Measured in metres. The more energy a wave has the bigger the amplitude is.
Frequency
this is the number of waves passing a point every second and is measured in hertz (Hz).
Calculating wave speed:
Wave speed = frequency x wavelength
what is wave speed?
The speed of a wave is how far a peak or trough moves every second.
period:
period T (seconds) = 1 / frequency (Hz)
frequency:
frequency (Hz) = 1 / period (s)
what is an echo?
When sound waves hit a smooth, hard surface they are reflected back towards their source. This means you hear an echo a few seconds after you make the original sound.
If the distance to the wall and the time delay are measured you can calculate the speed of sound in air using this equation:
speed = distance to object and back (2d) / time delay (t)
What will happen to the pitch if the frequency is increased?
It will increase. The higher the frequency, the higher the pitch.
Waves Required Practical - ripple tank
- Set up the ripple tank and switch on both the overhead lamp and the electric motor.
- Adjust the speed of the motor so that low frequency water waves are produced.
- Adjust the height of the lamp so that the pattern can be clearly seen on the card on the floor.
- Place a 30cm ruler at right angles to the waves shown in the pattern on the card. Measure across as many waves as possible then divide that length by the number of waves. This gives the wavelength of the waves.
- Count the number of waves passing a point in the pattern over 10 seconds. Then divide the number of waves counted by 10. This gives the frequency of the waves.
- Calculate the speed of the waves using the equation:
wave speed = frequency x wavelength
Waves Required Practical - string
- Switch on the vibration generator. A clear wave pattern should be seen and the nodes should look like they are stationary.
- Use a metre ruler to measure across as many half wavelengths as possible (a half wavelength is one loop) record the total length:
- Divide the total length by the number of half waves - This will give you the length of each half wave
- Double the length of the half wave to work out the wavelength.
- Calculate the speed of the wave using the equation:
wave speed = frequency x wavelength.
Bell in a vacuum demo
Sound waves are mechanical so they need a medium (particles) to travel. This means they cannot travel through a vacuum.
When the air is removed from the jar the sound can’t travel from the buzzer to your ear, so you can’t hear it.
