P7 Magnetism And Electromagnetism Flashcards
Permanent magnets always produce a
Magnetic field
Induced magnets become magnetised when
In another magnetic field
We draw magnetic field lines from
North to South
We can use mini compasses or iron filings to
Visualise a magnetic field
Three magnetic metals
Iron, Cobalt, Nickel
Aluminium and Copper are not
Magnetic
Opposite poles
Attract
Like poles
Repel
What is a solenoid
A long coil of wire that produces a magnetic field in and around the coil when there is a current in the coil
What is the motor effect
When a current is passed along a wire in a magnetic field, and the wire is not parallel to the lines of the magnetic field, a force is exerted on the wire by a magnetic field
What does the thumb, the first finger and the second finger tell you in Flemings left hand rule
thuMb = Motion
First finger = magnetic Field (N to S)
seCond finger = Current
How to do Magnetic flux density practical
-Place a magnet in a balance
-Measure the mass when known current is flowing
- Convert to Newtons (100g =1N)
-Measure length of wire in the field
-Rearrange F=BIL to find B
How does a motor work (motor effect)
6 steps
1) Ancurrent passes through the coil
2) This current creates a magnetic field
3) This magnetic field interacts with the magnetic field formed by the permanent magnet
4) This causes a force on the coil
5The force causes the coil to rotate
6) The split ring commutator reverses the current every half turn to keep the coil spinning in the same direction
How does a loud speaker work (motor effect) (6 steps)
1) A current passes through the coil
2)This current creates a magnetic field
3) This magnetic field interacts with the magnetic field formed by the permanent magnet
4) This causes a force on the coil
5)The current is alternating and changes direction, which changes the direction of the magnetic field and therefore the force
6) The changing force vibrates the cone. This causes air particles to vibrate and creates a sound
What is the generator effect
The production of a potential difference using a magnetic field
How does a generator work (6 steps)
1) A coil is moved in a magnetic field
2) The coil experiences a change in magnetic field
3) The coil “cuts” through magnetic field lines
4) This induces a potential difference
5) If there is a complete
6) then a current is also induced
How does a microphone work (6 steps)
1) Sound waves vibrate the diaphragm
2) The diaphragm moves the coil
3) The coil experiences a change in magnetic field
4) The coil “cuts” through magnetic field lines
5) This induces a potential difference
6) If there is a complete circuit, a current is also induced
What is the role of step up and step down transformers
To change the transmission voltage/p.d through the national grid, to reduce energy lost as heat due to resistance of cables
What is the order of the national grid
Power station➡️Step up transformer➡️national grid cables➡️step down transformer➡️homes
How does a transformer work (8 steps)
1) An alternating current flows in the primary coil
2)This creates a magnetic field that is changing in strength and direction
3)This field interacts with the secondary coil
4)The secondary coil experiences a change in magnetic field
5The coil “cuts” through magnetic field lines
6)This induces an alternating potential difference
7)If there is a complete circuit, the current is also induced
8)If there are more turns on the second arch coil compared to the primary coil, the voltage is “stepped up”
