Post on 07-Aug-2015
transcript
202/3 – Know the principles of electro-magnetism
Outcome 3.1 – Flux patterns of electromagnets
Unit 202 Principles of electrical science
3.1 Describe the magnetic flux patterns of electromagnets
Current carrying conductor, solenoid, magnetic poles, relays.
This session
When current flows in a conductor, a magnetic field is created around it.
Magnetic field around a current carrying conductor
Magnetic field around a solenoid
There is only a magnetic field when current is flowing.
This is called an electro-magnet.
When it is used operate something it is called a solenoid.
SolenoidsA solenoid occurs when a number of strands of wire are formed into a series of turns with nothing in them but air.
If the turns of wire are wound around a core it is termed as a coil.
If each turn of the coil is a conductor, then increasing the number of turns increases strength of the magnetic field.
If an iron-core were added then the strength of the magnetic field would increase dramatically.
The Strength Of The Magnetic Field
The strength of the magnetic field is determined by the number of times the conductor is wound around the coil.
If the number of turns is increased then so effectively has the number of conductors. This has increased the magnetic field.
It is also dependent on the size of the current.
If an iron core was added instead of air then the magnetic field would increase dramatically.
Solenoid uses
Door entry systemsNo current when locked, energised to open.
Gas safety valveEnergised while open, closes when emergency stop is pressed or power fails.
Door bellEnergised when pressed, ding. Dong when released.
Coils
If we want the extra magnetism that comes from having the current passing in the same direction we use a coil.
This is an air filled coil with very few lines of magnetic flux
The former here is made out of iron and there are many more lines of magnetic flux.
Coils
Material obviously plays an important part, remember all materials have their own individual magnetic properties.
Increasing The Current
There is a direct link between the current that a conductor carries and the strength of the magnetic field surrounding it.
When we combine the number of turn in the coil and increase the current we are dealing with magnetomotive force (m.m.f)
The magnetomotive force is the force that causes a magnetic field to be built up or
established
m.m.f (F) = current (I) x number of turns (N)
F = IN
Draw a 24v relay circuit that will turn a 230v light on and operate another
24v relay.
(it will need 2 x 2way switches)
Individual task
consolidation
3.1 Describe the magnetic flux patterns of electromagnets
Current carrying conductorsolenoid, magnetic poles, relays.