topic 6 - magnetism and electromagnetism Flashcards
what charges repel and what charges attract
Opposites attract: North attracts South and South attracts North
Like charges repel: Two Norths will repel each other
what is magnetic field line
- Around every magnet there is a region of space where we can detect magnetism (where magnetic materials will be affected).
- This is called the magnetic field and in a diagram we represent this with magnetic field lines.
- The magnetic field lines should always point from north to south.
what is induced magnetism
- When magnetic materials are bought near or touch the pole of a strong or permanent magnet, they become magnets. This magnetic character is induced in the objects and it is removed when the permanent magnet is removed. This is a temporary magnet
- an example of an induced magnet is paper clips. when brought to a permanent magnet a paper clip will become a temporary magnet
define magnetically hard
a material that is hard to magnetise and de-magnetise. it can retain its magnetic properties for a long time. it is used to make permanent magnets e.g. steel
define magnetically soft
a material that is easy to magnetise and de-magnetise. it doesnt retain magnetic properties for long. it is used to make temporary magnets e.g. soft iron
practical to show shape of a magnetic field
- place magnet on paper
- sprinkle iron filings all around it
- tap paper gently to reveal shape of magnetic field
practical to show shape AND direction of magnetic field
- place magnet on paper
- place plotting compasses all around it
- deflection of compass needle shows direction of field
- to find shape of field mark field lines with pencil
how to use two permanent magnets to produce a uniform magnetic field pattern
A uniform magnetic field is comprised of straight, parallel lines which are evenly spaced. Between two opposite charges on flat magnets, a uniform magnetic field is formed.
what is produced when there’s an electric current in a conductor
A current travelling along a wire produces a circular magnetic field around the wire.
what is the motor effect
- Current flows in the wire/coil.
- This creates a magnetic field around the wire/coil.
- This magnetic field interacts with the field from the permanent magnet.
- This produces a force on the wire/coil which moves the wire/coil.
- The split-ring commutator changes the direction of the current every half turn as it spins. This reverses the direction of the forces, allowing the coil to continue spinning.
how is the motor effect applied in loudspeakers
- An alternating current from the source passes though the coils in the speaker.
- This current is constantly changing direction and magnitude
- This current creates a magnetic field around the coil
- This field interacts with the magnetic field from the permanent magnets
- Creating a constantly changing force on the coil.
- This causes the coil to vibrate in and out as the direction of the force changes, moving the cone
- The cone causes vibrations which we hear as sound waves.
how to use flemmings left and rule
- thumb represents force (father)
- second finger represents magnetic field (mother)
- third finger represents current (child)
how does the force on a current-carrying conductor in a magnetic field change with the magnitude and direction of the field and current
If you increase the magnitude of the current through a wire or the size of the magnet being used, you increase the force on the wire.
If you change the direction of the current or reverse the poles of the magnet, you change the direction of the force on the wire
