p12 - p13 Flashcards
What magnetic poles attract and repel
same magnetic poles repel
opposite magnetic poles attract
Difference between permanent and induced magnets
Permanent magnet produces its own magnetic field
Induced magnet only becomes magnetic in a magnetic field
Permanent magnet always has a magnetic field
When taken out of magnetic field , an induced magnet will loose its magnetism
Describe magnetic field around bar magnet
What do the concentration on lines show ?
Field lines all have arrows
they all go from north to south
Field lines most concentrated at the poles so magnetic field strongest at the poles
closer the lines are the stronger the magnetic field
How can we use a compass to draw magnetic field lines
How does this show the earth has a magnetic field
place plotting compass near the magnet on a piece of paper
Mark the needle directions and move the compass to different areas in the magnetic field
Join the points to show the magnetic field lines
The behaviour of the compass shows us the earth has a magnetic field , this is from the earths core
Describe the magnetic field of a wire carrying a current - how can we detect this magnetic field
Also what makes the magnetic field stronger
Creates a circular magnetic field around the wire
we can detect this field because this field can deflect the needle of a compass
The higher the current , the stronger the magnetic field
We can use Flemings right hand rule
What is a solenoid and what does it do
Describe the magnetic field inside and around a solenoid
A solenoid is a coil of wire that strengthens a magnetic field .
Magnetic field inside a solenoid is strong and uniform
The field outside the solenoid is weak because the forces cancel out each other
What is the motor effect ?
Wire carrying a current has a magnetic field
this can interact with another magnetic field at a right angle to put a force on the wire
What is Flemings left hand rule ?
The direction of a motor effect can be calculate from Flemings left hand rule
F - Force
B - Magnetic field
I - Current
How to calculate motor effect force
4 components
Force = magnetic flux density(T) × current(a)× length(m) F= B x I x L
How is a wire used to make an electric motor
A coil of wire carrying a current in a magnetic field experiences a force that makes it rotate - this can be used to make an electric motor
Explain how to induce a potential difference using a magnet and a conductor
A potential difference can be induced when there is movement between a conductor and a magnetic field
A coil of wire moves in and out of a magnetic field
A magnetic field is moved in and out of a coil of wire
Factors affecting an induced potential difference from electromagnets
Speed of movement
Magnetic field strength
Number of turns in a coil
How is electromagnetic induction used in alternators to make an alternating current ?
A Coil is rotated in a magnetic field
As the coil moves up through the magnetic field , a current is induced in 1 direction
As this side of the coil goes down the other side of the coil will move up in the magnetic field and the current will be induced in the opposite direction
Slip rings connected to the coil
Current is constantly changing direction (a.c)
How is electromagnetic induction used in dynamos to make a direct current ?
A coil is rotated in a magnetic field
However the split ring commutator changes the coil connections every half turn
this means the current flows in the same direction
This makes it a direct current (d.c)
How does a microphone convert sound waves to an electrical impulse
They use the generator effect
Sound waves cause the diaphragm to vibrate
This then causes a coil of wire to move in a magnet
A potential difference is induced in the coil
The frequency of the change in potential difference is the same as the frequency of the sound waves
