Magnetism and Electromagnetism

Poles of a Magnet

where magnetic forces are strongest

Like Poles

Repel each other when brought close.

Unlike Poles

Attract each other when brought close.

Non-contact Force

Force exerted without physical contact.

Permanent Magnet

Produces its own magnetic field continuously.

Induced Magnet

material that becomes magnetised when placed in a magnetic field.

what does Induced Magnetism cause

Causes force of attraction

removing induced magnet from magnetic field

loses magnetism when removed

Magnetic Field

Region around a magnet where forces act on another magnet or on a magnetic material

magnetic materials

iron

steel

cobalt

nickel

Magnetic Field Strength

Depends on distance from the magnet

field is strongest at the poles of magnet

direction of magnetic field

the direction of force that would act on another north pole placed at any point

Compass

Contains a bar magnet; indicates Earth's magnetic field.

compass needles point in direction of earths magnetic field

how to draw magnetic fields with compass

• place plotting compass near magnet on piece of paper

• mark direction the compass needle points

• move the plotting compass to different positions in magnetic field, marking the needle direction

• join the points to show field lines

what pole does the needle of the plotting compass point to

South Pole

drawing Magnetic Field Lines

arrow heads are in direction from north pole to south pole.

lines never cross

closer the lines, stronger the magnetic field

when a current flows in a wire, it creates ..

it creates a circular magnetic field around a wire

when is the strength of the magnetic field greater

closer to the wore

if current is increased

solenoid

consists of a wire coiled up into spiral shape

increases strength of magnetic field created by a current through a wire

magnetic field inside a solenoid

strong and unifrom

magnetic field around a solenoid

has similar shape to field of bar magnet

Electromagnet

Solenoid with an iron core to increase strength.

how is a simple electromagnet made

by coiling a wire around an iron nail

what devices are electromagnets used in

electric bells

automatically locking doors

Motor Effect

a wire carrying a current creates a magnetic field

this can interact with another magnetic field causing a force that pushes the wire at right angles

what is length of wire measured in

metres

what is magnetic flux density

Strength of magnetic field per unit area.

measure in Tesla

Fleming's Left-Hand Rule

Determines direction of force on a conductor.

thumb represents

force(movement)

forefinger represents

magnetic field lines

north to south

second finger represents

current

positive to negative

when is force greatest in a current interacting with a magnetic field

when the direction is 90 degrees to direction of magnetic field

the force on a wirier a magnetic field increases when

current in wire increases-stronger magnets

strength of magnetic field increases

electric motor

a coil of wire carrying a current in a magnetic field experiences a force that tends to make it rotate.

describe the direction of the forces in the current in this diagram

current on the left hand side of coil causes downwards force

current on right hand side of coil causes upwards force

which direction would the coil rotate in this diagram

anticlockwise

when the coil vertical and is moving parallel to the magnetic field

there is no force

split ring commutator

changes the current every half turn so coil does a full turn

once conducting brushes reconnect with commutator after a half turn

current flows in opposite direction through the wire in the coil

each side of the coil is now near the opposite pole

Force Equation

F = BIl; relates force, magnetic field, current.

Magnetic Field Pattern

Visual representation of magnetic field strength and direction.

Compass Needle

Aligns with Earth's magnetic field direction.