Magnetism Flashcards
Laws of magnetism
Like poles repel
Unlike poles attract
What are the names of the 2 magnetic poles?
North
South
What are the only 3 elements that can be magnetised?
iron
cobalt
nickel
What magnetic element is steel an alloy of?
iron
What is a magnetic field line?
Shows the force in a magnetic field on another magnet
Field lines run north to south
Field lines never cross
Expt to show the pattern of a magnetic field around a permanent bar magnet?
Lay paper over the magnet/s
Spinkle iron filings
Tap the paper
Expt to show the direction of the magnetic field lines around a permanent bar magnet?
Place plotting compasses around the magnet/s
Draw on the paper below the direction of the needle
Join up the small arrows to get the magnetic field lines
Describe the pattern of the magnetic field around two magnets with N and S poles facing each other
Uniform field between N and S poles
Beetle shape around both magnets
Describe the pattern of the magnetic field around two magnets with N and N poles facing each other
Beetle shape around each magnet
Neutral point between N and N pole as the repel
Describe the magnetic field around a bar magnet
Beetle shape
Field lines run N to S
Field lines never cross
What is a magnetically hard material?
One that keeps retains its magnetism
eg steel
What is a magnetically soft material?
One that gains and looses magnetism easily
eg soft iron
How do you create a uniform magnetic field using 2 bar magnets?
Place magnets N facing S close to each other. Field in between in uniform
Shape of a mag field around a wire carrying a current and how to we determine its direction?
Circular
Use right hand grip rule
Construction of an electromagnet?
coil of wire
around a soft iron core
dc current supply
Shape of filed around a solenoid
same as a bar magnet
Shape of field around a flat coil
use right hand grip rule to work it out
Why is a force exerted on a current carrying wire sitting at right angles in a magnetic field?
Mag field of wire with current interacts with mag field of magnets to produce motion
Magnetism + current = motion
Does a charged particle moving at right angles in a magnetic field experience a force on it ?
Yes - as a charged particle is a tiny bit of current!
What is the motor effect and what hand rule do we use to determine direction of the movement?
Magnetism + current = motion
Fleming’s Left hand rule
How do you increase the size of the force in the motor effect?
Larger current
Stronger magnets
Coil more wire - more coils
What is electromagnetic induction and how do we determine the direction of induced voltage?
Magnetism + motion = current (induced voltage)
all at right angles
Fleming’s right and rule
Factors affecting the size of the induced voltage?
Stronger magnets
Faster movement
More coils
Motor effect or electromagnetic induction:
The loudspeaker?
motor effect
Motor effect or electromagnetic induction:
The motor?
motor effect
Motor effect or electromagnetic induction:
The generator?
electromagnetic induction
Motor effect or electromagnetic induction:
The microphone?
electromagnetic induction
Motor effect or electromagnetic induction:
The transformer?
electromagnetic induction
What does a step up transformer do?
steps up voltage
What does a step down transformer do?
steps down voltage
Why do we transmit electricity on the national grid at very high voltage?
High voltage means less energy lost as heat in wire as:
Power loss = I 2 R
For a 100% efficient transformer…..
Power in = power out
IV primary = IV secondary
Transformer turns equations:
primary V = primary turns
secondary V secondary turns
Describe stages of how a transformer works:
AC current passed through primary coil
Primary magnetic field grows
Soft iron core channels this changing mag field into secondary coil
Secondary coil cuts changing magnetic field
produces an induced voltage in secondary coil
What has to be happening for an induced voltage is produced?
The wire or coil must be cutting a magnetic field
