SOUND WITH FREQUENCIES HIGHER THAN 20,000 HZ.
- Electrical devices can produce electric oscillations (,basically sound) of any frequency. These can be converted into MECHANICAL VIBRATIONS to produce sound waves beyond human hearing, this is ultrasound.
Ultrasound waves get reflected at a boundary between media.
- When a wave passes through mediums, some if REFLECTED and some is transmitted, this is partial reflection.
- This means you can point an ultrasound pulse at an object and wherever the boundaries are; some wave will be reflected back.
Ultrasound is useful.
SCANNING OF A FOETUS.
- when ultrasound waves reach a boundary, some wave is reflected. So when the ultrasound wave passes through the fluid in the womb to the skin of the foetus; some wave is reflected back and detected.
- Timing and distribution of these echoes are processed by a computer to create an image of the foetus.
- Boats and submarines use sonar to detect things around them.
- By emitting waves of ultrasound that reflect of thing around them (ie other boats or animals) waves are reflected back to the boat.
- computers time the delay between emitting and detecting to calculate how far away other objects are.
- Animals, like bats, sense things around them in a similar way.
FREQUENCIES LESS THAN 20 HZ
- long wave lengths = travel long distances and diffract around objects easily.
- ie elephants and tigers use infrasound to communicate.
- meteor strikes and volcanic eruptions produce infrasound which means we can detect them from far away.
Tectonic plates and the earth.
The crust and the upper part of the mantle are split into large pieces called 'tectonic plates.'
Convection currents cause these plates to drift.
At plate boundaries, the plates may slide past eachother, this causes earthquakes.
The Earth's structure
1) We live on the crust, it's very thin.
2) Below the crust is the mantle, it's basically a solid, but it can flow very slowly. This is where radioactive decay takes place, which produces heat, which causes the mantle to flow in convection currents.
3) The Earth's core is at the centre. The inner core is solid, but the outer core is liquid.
Earthquakes and explosions cause seismic waves.
We detect these waves using seismometers.
P-waves are longitudinal. They are fast and can travel through solids and liquids.
S-waves are transversssssssse. They can only travel through solids.
Like usual, when a wave reaches a boundary some of it is reflected.By observing how waves have been reflected and refracted, scientists have been able to observe the earth.
Most of the time, wave speed changes gradually, which results in a curved path. But the path can have a kink when the properties suddenly change.
P-waves and s-waves travel at different speeds, so on a seismogram, you'll see two different tremors. Measuring the time difference can calculate how far away the earthquake was.
Then, you draw a circle on your map centred on your location of your seismometer with the distance you calculated as it's radius. The distance arc of 3 or more seismometers will overlap at one point, giving the location of the earth quake. This is called triangulation.
Current is the flow of charge round a circuit.
Voltage (or potential difference) is an electrical pressure giving a measure of the energy transferred.
If you increase the voltage, you also increase the current.
Electrons in a current flow opposite to the flow of 'convential current.'
Alternating current, for example the mains in your home, is a current that keeps reversing back and forth. It has a wave on an oscilloscope.
Whereas direct current always flows in the same direction and just comes up as a line. This is found in batteries and solar cells.
Electrical power is the energy transferred per second.
Electrical appliances are useful because they take in electric energy and convert it into other forms of energy.
You measure power in 'watts.'
The higher the power, the more energy transferred per second.
power equals current times voltage.