ULTRASOUND : sound with a higher frequency than we can hear -used for cleaning, quality control, pre-natal scanning and bats
cleaning: the high frequency vibrations of ultrasound make the components of a piece of equipment vibrate at a high frequency. The dirt on the equipment vibrates also. Dirt simply then falls off.
quality control: waves can pass through something like a metal casting and when they reach a boundary between two different media, some of the wave is reflected back and detected. If there are cracks, they'll be detected.
Pre-natal scans: Same principle as quality control. Wave reflected back when hits boundaries between different media. There is the boundary between amniotic fluid and tissue of the baby/fetus. Reflected waves are processed by computer and come up as a video image of the fetus. Checks baby is developing correctly and see the sex.
Bats: Similar technique to pre-natal scans. They send out ultrasound squeaks and their big ears pick up the reflections. Their brains process the reflected signals and turn them into an image to see.
MAGNETIC FIELD: a region when magnetic materials (e.g. iron or steel) and also wires carrying currents, experience a force acting on them.
The magnetic field around a solenoid (COIL OF WIRE):
-strong and uniform
-outside the coil, the magnetic field is just like the one round a bar magnet
-the ends of the coil of wire (solenoid) act like the north and south poles of a bar magnet
-if the direction of the current changes, obviously the the North and South poles swap ends.
You can increase the strength of the magnetic field by adding a soft iron core through the middle of the coil. This then becomes an ELECTROMAGNET.
The iron does not stay magnetised when current is turned off and magnetic field disappears. IRON, STEEL AND NICKEL ARE MAGNETIC.
The Motor Effect
Passing a current through a wire produces a magnetic field around the wire. If you put that wire into a magnetic field, you have TWO magnetic fields combining. This puts a force on the wire.
Basically A CURRENT IN A MAGNETIC FIELD EXPERIENCES A FORCE.
Fleming's left hand rule (motor effect)
thuMb=Motion, First finger=Field, seCond finger=Current
The simple electric motor
THE SIMPLE ELECTRIC MOTOR
4 factors which speed it up:
1) more CURRENT
2) more TURNS on the coil
3) STRONGER MAGNETIC FIELD
4) a SOFT IRON CORE in the coil
Electric motors are used in CD players, food mixers, fan heaters, fans, printers, drills, hairdryers, cement mixers etc....
ELECTROMAGNETIC INDUCTION: the creation of voltage (and maybe current) in a wire which is experiencing a change in magnetic field.
'induction' is just another word for 'creation'
Moving a magnet in a coil of wire induces (creates) a voltage
You can create a voltage (&maybe a current) in a conductor by moving a magnet in a coil of wire or moving a conductor in a magnetic field. Shifting the magnet from side to side creates a little 'blip' of current.
GENERATORS generate electricity and it's all down to electromagnetic induction.
AC GENERATORS-just turn the coil and there's a current
-generators rotate a coil in a magnetic field
-their construction is like a motor
-as the coil spins, a current is induced (created) in the coil. This current changs direction every half turn.