Magnetism and Electromagnetism Flashcards
What do magnets produce
Magnetic fields
Magnetic field
Region around magnet where other magnets or magnetic material experience a non-contact force of magnetism
Direction of magnetic force
North to South
Magnetic materials
- iron
- steel
- nickel
- cobalt
What do magnetic field lines show
Which way a force would act on a north pole if it was put at that point in the field
What do closer magnetic field lines show
Stronger magnetic field
What determines strength of magnetic field
Distance from magnet
Where is magnetic field strongest
At poles of magnet
What is force between magnet and magnetic material always
Attractive
How do compasses work
- contain tiny bar magnet inside
- north pole of magnet attracted to south pole of any nearby magnet
- compass needle points in direction of magnetic field
How to use compass to trace magnetic field
- move compass around magnet
- trace position of arrow on paper
Where do compasses point when not near a magnet
(geographic) North
What gives Earth its magnetic field
Magnetic core
What provides evidence for Earth’s magnetic core
Behaviour of magnetic compass
Types of magnet
- permanent
- induced
Permanent magnet
- produce own magnetic field, can’t be turned on/off
- can attract or repel
Induced magnets
- only produce force of attraction when in magnetic field of another magnet
- when magnetic field removed, loses most/all magnetism quickly
- can only produce force of attraction
What creates magnetic field around wire
Current flowing through wire
What makes up magnetic field around wire
Concentric circles perpendicular to wire, with wire in centre
Effect of changing direction of current
Changes direction of magnetic field
Right-hand thumb rule
- thumb points direction of current
- fingers curl direction of magnetic field
What affects magnetic field strength around wire
- current size
- distance from wire
- solenoid
How does current size affect magnetic field strength
Larger current = stronger
How does distance from wire affect magnetic field strength
Closer to wire = stronger
Solenoid
Coil of wire
How does solenoid affect magnetic field strength
Wrapping wire to form solenoid = stronger
Why does solenoid increase magnetic field strength
- field lines around each loop line up with each other
- results in lots of field lines pointing in same direction, close together
How to increase field strength of solenoid
- turn it into an electromagnet
- put block of iron into centre of coil, iron core becomes and induced magnet
Electromagnet
Solenoid with an iron core, has magnetic field that can be turned on/off with electric current
Motor effect
- current-carrying wire placed between magnetic poles
- magnetic field around wire interacts with magnetic field it is placed in
- causes magnet and conductor to exert force on each other
- causes wire to move
How do angles affect force experienced in motor effect
- wire at 90° to magnetic field - experiences full force
- wire parallel - experiences no force
- wire at angle between - experiences some force
What angle does force act at in motor effect
- right angle to magnetic field of magnets
- right angle to direction of current in wire
How does magnetic field strength affect magnitude of force
As field strength increases, magnitude of force increases
How does amount of current passing through conductor affect force
As amount of current increases, force increases
What affects force acting on conductor in magnetic field
- magnetic flux density
- size of current of conductor
- length of conductor in magnetic field
Magnetic flux density
How many field (flux) lines there are in a region, showing strength of magnetic field
When can FBIL equation be used to find force
When current is at 90° to magnetic field it’s in
Unit of magnetic flux density
Tesla (T)
Fleming’s left hand rule
- thumb and 2 fingers perpendicular to each other
- thumb shows direction of force
- index finger shows direction of magnetic field
- middle finger shows direction of current
How does electric motor work
- current flows in opposite directions on each side
- magnetic field always acts in same direction (N-S)
- causes forces acting up and down
- causes coil to spin
Split-ring commutator
- swaps contacts every half turn
- causes current to reverse every half turn
- so motor keeps spinning in same direction
How to reverse direction of motor
- swapping polarity of dc supply - reverses current
- swapping magnetic poles - reverses field
How to increase speed of electric motor
- increase current
- add more turns to coil
- increase magnetic flux density
