Topic 12- Magnetism and the Motor effect Flashcards
What are magnets?
Material that produces a magnetic field and is attracted to the opposite pole (North to South) (South to North)
What are permanent magnets?
-Create their own magnetic field
What are permenant magnets used for?
magnets
-Speakers (vibrations)
-Electric Generators
-Compasses
How do microphones work?
1) Sound waves vibrate the diaphram
2) Coil is attached to the diaphram so vibrates aswell
3) Coil vibrates over a permenant magnet, and thus in a magnetic feild
4) This induces a current
How do electric generators work?
-Push and pull out a magnet from a coil of wires
-Always wants to prevent this movement
e.g put in north pole, (wire acts as north pole) take out north pole (wire acts as a south pole)
What is an induced magnet?
magnetic material
-Metal placed inside a magnetic field and gains its own magnetic field
-Temporary
-Made of iron, nickel or cobalt (steel)
domains point to one side instead of cancelling out
Magnetically Soft vs Hard materials?
- Soft= loose magnetic field quickly (nickel + cobalt)
- Hard= loose magnetic field slowly (iron
What is the magnetic field around a bar magnet?
-North to south
-Around in rings
What is the magnetic field of a North and South pole?
-Uniform
How to use a compass to describe magnetic field?
1) Place magnet on paper
2) Draw around it
3) Plot compass and follow the needle
4) Repeat
How do magnetic compasses prove the Earth has a magnetic core?
-Freely suspended compass aligns itself with the earths magnetic field lines
-Earth’s magnetic North pole is the South pole (and vice versa)
What does a long straight conductor create?
- A wire with a current creates a magnetic field
How to prove a current has a magnetic field?
1) Place wire through card
2) Add iron shavings
3)Turn on current
What doees the magnetic field around a wire look like?
-Circles that get further away
-Strongest closest
Weaker= the further away or lower the current
How to make the magnetic field stronger?
-Field lines have a higher concentration
-Stronger magnet
-Increase coils of wire
-Add iron core
Describe the magnetic field of a solenoid?
The centre:
1) Many magnetic fields add up in the centre
2) Form a uniform, bar like magnet field
—-> Strong
The outside:
1) Many magnetic fields cancel out
—->Weak
Why does adding an iron core to a solenoid increase the magnetic field strength?
-Easier for magnetic field lines to pass through than air
If a current goes away from you, which way is the magnetic field?
(symbol=x)
Clockwise
How do currents and magnetic fields interact?
-Two types of magnetic fields interact
-Cuases a force (movement/ kick) where they cancel out
What is Flemings left hand rule
-FBI
- (Magnetic) Force
- Magnetic field line (uniform)
- Current
What is the equation linking FBI?
Perpendicular forces to magnetic field= Magnetic flux density x Current x Length
F=BxCxL
What is magnetic flux density measured in?
-Tesla (T)
-Newton per Amp metre (N/Am)
How do motors work?
Only 180 degrees turns?
1) Circuit of wire between two permenant magnets
2) Current is passed though wire (positive to negative terminal)
3) Force cuases wire to move one way than the other
4) Force stops when wire is perpendicular to the uniform field lines (strongest when horizontal/moves perpendicular to magnetic field)
Potential difference at verticle/ parallel movement = 0 (continues movement due to momentum)
How to make an electrical motor turn 360 degrees?
1) Add alternating current
2) Use a split ing commutator
3) Every half turn it swaps the positive and negative terminals (changees current direction)
Motor vs Generator?
Motor=moves by itself
Generator= We move it
