Magnetism Flashcards
(28 cards)
Magnetism and magnetic materials
Magnets attract to objects containing iron, steel, nickel
Magnetically hard
Hard to demagnetise, will retain magnetism once other magnet is removed
Steel
Magnetically soft
Easy to magnetise and demagnetise but will lose magnetic ability when other magnet removed
Magnetic fields
Symmetrical
Field lines close together at poles
No crossover
Hairy hamburger
How to find magnetic field lines
Use plotting compass
Place compass on the end of one pole and put a dot where the tail of the needle is
Place compass tail on dot and put another dot on where the other side of the tail is
Repeat
Join lines together in a curve
N=>S
Laws of magnetism
Similar poles repel
Opposite poles attract
Uniform magnetic field between poles
How to make a magnet
Atom, tiny magnet called dipole
Many dipoles, domain
If unaligned, domains cancel out
If domains line up, magnetic
Electromagnetism
Magnetic field will be established around current carrying wire
Circular magnetic field
Right hand grip rule
Thumb, current
Fingers, field direction
Dart needle, towards
Tail away
Magnetic field around a solenoid
Solenoid has north and South Pole
Like a bar magnet
Solenoid can be strengthened by
More coils
Iron core
More current
Uses of electromagnetism
Relays, small voltage used to switch a larger cola tape appliance on
Circuit breakers, circuit broken if excess current flows caused by malfunction
Electric bell
Loudspeaker, uses AC and permanent magnet to cause movement
The motor effects
When 2 field lines cross, wire experiences a force when in a magnetic field
FLHR
Force on charged particle when it moves in a magnetic field as long as the motion is not parallel to the field
FLHR
Thumb, motion
First finger, field
Second finger, current
How to change the direction of induced force
Flip the battery
Flip the magnet
How to increase the force induced
Add more current
Increase magnetic field strength
Increase no of wires
Generators
Convert mechanical energy into elec energy
DC motor
Converts electrical energy and magnetism into movement N=>S Coil rotates, cuts through field lines Induces current in coil 1 terminal, always + 1 terminal, always - Direction of current does not change Split rings rotate with coil
Increase motor strength
More coils on rotating part
Increase current flow
Increase magnetic strength
Increase area of coil
Electromagnetic induction
Is a wire is moved through a magnetic field, a current is produced
Induction also occurs if a magnet is moved in a coil of wire or if a coil of wire rotates in a magnetic field
KE=>electrical
Faster movement, higher pd generated
FRHR
Thumb, motion
First finger, magnetic field
Second finger, current
How would movement of magnet affect galvanometer
More KE=>more elec energy, galvanometer will show more current
Change direction, change direction of current
More coils, more induction of current
Stronger magnet, greater induced current
No movement, no change on galvanometer
AC generator
Magnetic field from N=>S
Cutting through magnetic field lines as coil rotates which induces a current in coil
FRHR shows that current is in diagram
One slip ring, +
Other slip ring,-
Half a cycle later, coil in field has rotated 180, reverses current in circuit
How to increase voltage in generators
Spin it faster
Stronger magnet
Larger number of coils
Larger area of coils
