P4.2 - Uses of Magnetism Flashcards
in line with spec
what is the ‘motor effect’?
when two ‘magnets’ exert a force upon each other
- but remember a wire can also be a magnet (ie. have a magnetic field produced around it)
what is produced when a current flows in a wire?
a magnetic field around it
what is the equation to calculate the size of the force exerted on a wire?
- first answer which factors it depends on
strength of magnetic field, current in wire, length of wire
F = B x I x L
b = magnetic flux density i = current l = length of conductor
what is the unit for magnetic flux density?
Tesla (T)
which rule is used to calculate the direction of the force on the wire?
fleming’s left hand rule
which finger is which on fleming’s left hand rule?
first = field second = current thumb = force
how does a magnet and current-carrying wire exert a force on one another?
- whenever a current flows in a wire a magnetic field is generated around it
- therefore it has magnetic field lines
- the field lines of the magnet and current-carrying wire interact and exert a force on one another
how do you determine whether forces applied between magnets (or a wire) is repulsive or attractive?
- if currents in wire in same direction = attractive
- if currents in wire in opposite directions = repulsive
what does a split ring commutator do?
and why does it do that
- reverses the direction of the current in the coil every half turn of the coil
(within a motor) - but allows current to flow the same way to the battery
- to ensure the coil rotates in the same direction (and not flip-flop)
how would you increase the speed of a motor?
- increase the size of the force acting on the wire
SO
- increase current in coil
- increase strength of magnet/ B-field
- have more loops
- longer length of wire
describe how a motor rotates
1) the motor contains a wire with a current running through it within a magnetic field
2) therefore the wire experiences a force upon it
3) as current flows in different directions of the coil, opposite forces act upon it which causes it to rotate
4) it reaches the middle and is now upright
5) as the current is no longer running perpendicular to the magnetic field, no force is produced
6) therefore, its momentum turns it over to the other side
7) once rotated, both sides would have switched position and would rotate the opposite direction to before
8) to prevent the coil from flip-flopping, a split ring commutator reverses the current direction every half turn (so the coil can rotate in the same direction)
how would increasing the current in a wire increase the force on the coil?
- larger current = greater magnetic field line density around wire (current in wire = magnetic field lines)
- and so greater interaction between wire and permanent magnet’s field lines
- interaction is exerting a force on one another*
what does an electrical motor use the motor effect to do?
transfer electrical energy to kinetic energy
what is electromagnetic induction?
when a conductor cuts the magnetic field lines of a magnet, and a potential difference is induced across the end of the conductor
OPPOSITE OF MOTOR EFFECT
kinetic energy -> electrical energy
describe how electromagnetic induction produces a current
1) when a wire cuts magnetic field lines perpendicularly
2) electrons are moved to one side of the conductor
3) which produces a potential difference
4) and so if the wire is part of a complete circuit, a current would flow
what process is used for generators to produce electricity?
electromagnetic induction
what is the main principle to increase the size of a potential difference produced?
increase the RATE of cutting magnetic field lines
what 3 factors increase the size of p.d generated within a wire?
- increase number of coils in the wire (more magnetic field lines produced)
- use a stronger magnet
(denser field lines) - move the wire quicker through the magnetic field (more field lines cut)
how would reversing the direction of the movement of a wire affect the voltage?
reverse direction of induced voltage
would a potential difference be induced if a wire was moving parallel to the magnetic field lines?
no, they must be perpendicular (to cut field lines)