Magnetism and Electromagnetism

how is the strength of a magnetic field shown?

• if magnetic field lines are closer, then magnetic field is stronger

• if lines are further apart then magnetic field is weaker

what is a permanent magnet?

produces its own magnetic field

what is an induced magnet?

material that becomes a magnetic when placed in a magnetic field

what are examples of magnetically hard materials?

steel

what metals can only be temporarily magnetised?

iron

what is the magnetic field like when you place two attracting magnets in front of each other?

uniformed field lines, lines are equally spaced and parallel

what is the magnetic field likes when you place tow repelling magnets in front of each other?

there is a null point in the middle where magnetic material feels no force, and magnetic field lines go sideways

what is a hard magnetic material?

can be permanently magnetised and difficult to magnetise

what is a soft magnetic material?

materials that can lose their magnetism easily and temporarily be magnetised

describe an experiment to determine shape and direction of magnetic field produced by bar magnet?

• use plotting compass and place above north side of magnet

• mark top of plotting compass

• place plotting compass on mark and repeat until you reach the south pole

• repeat this 3 times on both sides

how can you reverse the direction of the magnetic field?

reverse the direction of the current

how can you increase the strength of the solenoid?

increase current

increase number of turns on coil

explain why a current carrying wire experiences a force on the magnetic field?

• current carrying wire has a magnetic field around it due to the current

• this interacts with the magnetic field of the permanent magnet

• leading to a force on the wire

explain why rolling rod rolls towards right end of the rails?

current carrying wire has a magnetic field which interacts with magnetic field of permanent magnet, this creates a force on the wire. The force is a maximum as the magnetic field and current are at right angles to each other, the direction of the force is found using left hand rule

how can you make a motor spin faster?

• increase current

• increase turns on coil

• increase strength of magnetic field

how can you reserve the direction of the motor?

• reverse direction of current

• reverse the magnetic field

how does a motor work?

• a current passes through the coil,

• this creates a magnetic field which interacts with the magnetic field of permanent magnet.

• This creates a force on the coil.

• the Direction of the force is found using flemings left hand rule.

• the forces on opposite sides of coil are in opposite directions causing the coil to rotate

• split ring commutator changes direction of current every half turn so coil spins in same direction

how does a loudspeaker work?

• current passes through coil,

• this creates a magnetic field which interacts with magnetic field of permanent magnet

• creating a force on the coil

• the current is alternating and continuously changing direction

• so direction of magnetic field constantly changed direction and so does the force

• the changing force vibrates the cone causing the air particles to vibrate creating a sound wave