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Transcript of Electromagnetism
A piece of iron with coil wound around it which will only have magnetic properties when current flows through the coil.
EG. Fire Alarms
consists of an electromagnet, armature and contacts
When the switch is pressed the electromagnet is energised, this attracts the armature towards it, and towards the bell, with enough force to overcome the spring and strike the bell.
At the same time the contacts (one side connected to the armature) are broken.
This opens the circuit, the electromagnet loses its magnetism and the armature is released back to its resting place closing the circuit and starting the process again.
Electric Door Locks
Used for security and safety purposes
One type uses an electromagnet inside the door to pull the latch open when energised, letting the door be opened
The other type has an external electromagnet bolted to the door frame and a piece of iron bolted to the door.
This type, when energised, can either hold the door closed for security,
or hold doors open and automatically release them, eg. smoke-stop doors.
Moving Coil Instruments
Used in analogue meters
Consists of: Current carrying coil, Pivoting armature, Permanent magnet, Spiral hair springs
The coil is wound around the pivoting armature , which when energised, creates a magnetic flux
This flux apposes the magnetic field of the permanent magnet which creates a torque and rotates the armature
The hair springs return the needle to the rest position
Big versions of the electromagnet nails.
Consists of: Heavy gauge current carrying wire, Iron core.
The wire is coiled around the iron core and is energised.
This creates a magnetic flux strong enough to lift varying weights depending on the size of electromagnet. Like the next video.