3.3 Magnetic Fields Flashcards
What does a magnet have?
North and south pole
A magnetic field
What shows a magnetic field? How?
Iron filings
Shows the magnetic field lines
When drawing a magnetic field lines which way do they go?
From North to South
What does an electromagnet need?
The three C’s
Core
Coil
Current
How is an electromagnet made?
When current flows through a wire a magnetic field is created around the wire
The magnetic field magnetises the iron core
What materials are good for a core in an electromagnet?
Iron
Nickel
Cobalt
Steel (only for permanent)
How do you make an electromagnet stronger?
More turns on the coil
Increase the current
Use an iron core
What are the uses of an electromagnet?
Scrapyard crane The electric bell The circuit breaker Relay switch Electric motor
How does a relay switch work?
When the switch is closed the current flows - circuit is complete
The magnetic field attracts the arm causing the contacts to close
The current then flows around the larger circuit
How does the electric bell work?
When you complete the circuit by closing the switch current flows
The electromagnet’s magnetic field attracts the arm that hits the gong
When it does this the circuit breaks
Therefore the cycle repeats until switched off
What does a circuit breaker do when the current goes above 15A (the norm for this circuit)?
The electromagnet becomes stronger attracting the iron bolt down
This will release the plunger which is now not holding the switch
This breaks the circuit stopping current flowing to the rest of the circuit
What is flemings left hand rule?
MFC
Motion
Field
Current
