Magnetism and Electromagnetism Flashcards
what do magnets do?
repel and attract other magnets and attract other magnetic materials
what are non-magnetic materials?
materials that are not attracted to magnets and cannot be magnetised
what are examples of non-magnetic materials?
- glass
- plastic
what are magnetic materials?
materials that are attracted to magnets and can be magnetised
what are examples of magnetic materials?
- iron
- steel
- nickel
- cobalt
how can magnetism be induced in magnetic materials?
by placing them in a magnetic field
what is an example of
a magnetically hard material?
steel
what are magnetically soft materials?
magnetic materials that are only temporarily soft
what are magnetically hard materials?
magnetic materials that can be permanently magnetised
what is an example of a magnetically soft material?
soft iron
what do magnetic field lines represent?
the magnetic force on a north pole at a given point
what does the direction of a magnetic field line show?
the direction of the force
what does the distance between the magnetic field lines show?
the magnitude of the force
what direction do magnetic field lines point?
from north to south
what does a uniform magnetic field look like?
the field lines are parallel and evenly spaced
what does an electric current passing through a conductor produce?
a magnetic field around it
what do electromagnets consist of?
a coil of wire wrapped around a magnetically soft core and can be turn on and off
what is the motor effect?
a force acts on a current-carrying conductor in a magnetic field - Fleming’s left hand rule shows the relative directions of the force, field and current
if the current is reversed or the magnetic field is reversed…
the force will be reversed
if the magnitude of the current or of the magnetic field is increased…
the magnitude of the force will increase
what do DC motors consist of?
a coil of wire in between two permanent magnets
how do DC motors work?
- direct current flows through the wire and it experiences a turning effect due to the forces exerted on it in the magnetic field
- as the current flows in opposite directions on each side of the coil, the forces on each side are in opposite directions, making it turn
how can the turning effect in DC motors be increased?
- by increasing the current
- by using a stronger magnetic field
- by increasing the number of turns on the coil
what is a split ring commutator used for?
to ensure that the direction that the current flows in the coil reverses every half turn
what do loud speakers consist of?
a coil attached to a cone in a magnetic field
how do loud speakers work?
- when alternating current flows through the coil, the cone is continuously pushed away and pulled back, making a sound
- the frequency of the sound can be altered by changing the frequency of the alternating current used
why is a force exerted on charged particles in a magnetic field?
because moving charged particles are current as long as they are not moving parallel to the field
what is the generator effect?
- when there is a relative movement between conducting wire and a magnetic field, a voltage will be induced
- for example, if conducting wire moves across a magnetic field, a voltage will be induced in it
- if it is part of a complete circuit, this causes a current to flow
how can induced voltage be increased in electromagnetic induction?
- by moving the wire more quickly
- using a stronger magnetic field
- increasing the length of the wire inside the magnetic field
can a voltage be induced in a coil with a changing magnetic field through it?
yes - for example, when a magnet is moved into a coil, a voltage is induced in it
the more quickly the magnetic field changes…
the greater the voltage
how can electricity be generated?
- by rotating a magnet within a coil or by rotating a coil in a magnetic field
- as they rotate, the magnetic field through the coil changes, which induces a voltage and therefore a current in the coil
how can voltage be increased when generating electricity?
- by increasing the length of wire inside the magnetic field
- by using a stronger magnet
- by increasing the speed of rotation
what does a transformer consist of?
two coils wrapped around a soft iron core and is used to change the size of a voltage?
what are transformers used for?
- to step up the voltage (to a greater value) for transmission in power lines which reduces power loss (because lower current causes less power loss due to the resistance of the cables)
- then step down the voltage for usage in homes (to keep us safe)
what does an alternating voltage produce in the primary coil?
an alternating current - this creates a changing magnetic field which links with the secondary coil and induces an alternating voltage in it
a step-up transformer has more turns on the secondary than the primary which means…
the voltage of the secondary is greater than that of the primary
a step-down transformer has fewer turns on the secondary than the primary which means…
the voltage of the secondary is less than that of the primary
