short radio waves
Short-wave radio waves have wavelengths between 10 and 100m. These waves do not diffract around large objects however they reflect off the ionosphere (an electrically charged layer of gas in the upper atmosphere). This also allows communication with transmitters or receivers that are not in the line of sight. Bluetooth communication devices also use short-wave signals to transfer radio waves over short distances.
long radio waves
Long radio waves have wavelengths between
1 and 10km
These radio waves diffract around large objects such as hills
Radio waves
-The ac supply causes electrons in the transmitter to oscillate.
-These electrons produce radio waves which are transmitted over as distance.
-At the receiver, the radio waves cause electrons to oscillate.
-The electrons produce an ac current in the receiver.
very short waves
Radio waves used to transmit signals for TV and radio use very short wavelengths. These waves do not diffract around large objects or reflect off the ionosphere and so the transmitter and receiver need to be in the line of sight of one another.
how do transverse waves work?
When a wave travels through a medium, the particles in that medium vibrate. The particles transfer energy from one another as they vibrate.
In transverse waves, the vibrations of the particles are perpendicular to the direction of energy transfer.
Examples of transverse waves :
water waves,
waves on a string,
electromagnetic waves.
how do longitudinal waves work?
In longitudinal waves, vibrations of the particles are parallel to the direction of energy transfer.
Longitudinal waves have compressions where particles are squashed together, and rarefactions where particles spread apart due to the vibrations.
examples of longitudinal waves
sound waves
seismic P-waves.
Amplitude
the maximum displacement of a point on the wave from its undisturbed position.
Wavelength
the distance from a point on one wave to the equivalent point on the next wave (e.g. crest-to-crest or trough-to-trough).
Frequency
the number of waves passing a point per second.
measuring sound waves
Set up the oscilloscope so that each of the microphones are connected separately.
Turn on the signal generator and make a note of the frequency, f that you have chosen.
Begin with both microphones next to the speaker. The waves on the oscilloscope should line up, as shown in the diagram.
Move one microphone away from the other slowly. As it moves away, the waves on the oscilloscope will change.
When the waves on the oscilloscope line-up again, stop moving the microphone. The distance between the microphones is the wavelength,
λ of the sound.
Measure the distance between the two microphones using a meter rule.
Calculate the speed of sound using
v=fλ.
Required Practical
Measuring the Speed of Water Waves
In a darkened room, set up the experiment as shown in the diagram.
Switch on the signal generator so that the dipper produces waves.
Using the meter ruler, measure the distance between the shadows of the waves on the screen.
Choose two points on the screen and measure the distance between them.
Using a stopwatch, measure the time taken for a wave to travel between the two points.
Calculate the speed of the wave using
speed = distance / time
Required Practical
Investigation into Reflection Off Different Materials
Use a ruler to draw a straight line on a piece of paper.
Place an object on top of the piece of paper so one of its edges lines up with the straight line you have drawn.
Shine a ray of light at the object and trace the outline of the incoming and reflected beam on the piece of paper.
Draw the normal to the straight line at the point that the light hit the object.
Measure the angle of incidence and angle of reflection of the object using a protractor.
Measure the width of the incident and reflected beams.
Repeat for a range of objects, made from different materials.
The angle of incidence
is the angle between the incoming wave and the normal to the material boundary.
How do we Hear Sound?
Sound waves travel into your ear and cause the ear drum to vibrate. The ear drum passes on the vibrations to the ossicles (very small bones), through the semicircular canals and finally to the cochlea.
The cochlea coverts the vibrations to electrical signals which are transported to your brain along the auditory nerve.
Medical Imaging
Ultrasound waves can pass through the body. However, when they reach a tissue boundary, some of the wave is reflected back. When ultrasound waves are projected into the body, the time taken for the same waves to be reflected back out of the body allows us to work out how far into the body the tissue boundary is. This can be processed by a computer to create an image of inside the body.
A common application of ultrasound imaging is pre-natal imaging of a foetus. This is much safer than imaging the foetus with X-rays because sound waves are non-ionising.
Industrial Imaging
Similar to in medical imaging, ultrasound can be emitted into pipes or materials to find out about the inner structure of the material. Usually, the ultrasound wave will be reflected from the far side of the material. However, if there is a fault in the material it will be reflected sooner. The time taken for the echo to return to the detector is used to determine the position of the fault.
Echolocation
Ultrasound can be used by boats and submarines to measure the depth of water or locate objects under the water. The time taken for ultrasound waves to reflect off the sea bed and return to the boat or submarine tells us how much distance there is between the sea bed and the bottom of the boat or submarine.
when are seismic waves produced?
If an earthquake or volcanic eruption occurs
how are seismic waves detected?
using seismometers
what are the two types of seismic waves?
P waves – these are longitudinal waves that travel at different speeds through solids and liquids.
S waves – these are transverse waves that cannot travel through liquids.
