6 Magnetism and Electromagnetism Flashcards
MAGNETISM AND ELECTROMAGNETISM
properties of magnetically hard materials
e.g. steel
retain their magnetism once magnetised.
hard to magnetise
properties of magnetically soft materials
e.g. iron
lose their magnetism once they are no longer exposed to a magnetic field. They are used as temporary magnets such as electromagnets.
easily magnetised
define magnetic field line
(3 points)
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.
magnetism is induced in some materials when placed in a _________
magnetic field
describe how magnetism is induced in some materials when placed in a magnetic field
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
Magnetism is induced in the paperclips so each paperclip can attract another one
practical: investigate the magnetic field pattern for a permanent bar magnet and between two bar magnets
Place your bar magnet in the centre of the next page and draw around it.
Place a compass at one pole of the bar magnet.
Draw a ‘dot’ to show there the compass is pointing,
Move the compass so the opposite end of the needle is pointing to the dot,
Repeat steps 3 and 4 until to reach the other pole of the magnet.
Do this procedure at least 5 times from different points on the pole of the magnet.
Tip, try to be as accurate as possible when drawing your dots
Join up your dots to create the field line plots
describe 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.
How to draw:
from north to south
at least 3 lines with arrows pointing n-> s
evenly spaced (measure with ruler)
draw with ruler
an electric current in a conductor produces a ________ __________around it
magnetic field
how can magnetic field direction be determined in a current travelling along a wire
Right Hand Grip Rule
A current travelling along a wire produces a circular magnetic field around the wire
Describe the construction of electromagnets
A soft iron core wrapped in wire. When current flows through the coil of wire it becomes magnetic.
draw magnetic field patterns for a straight wire, a flat circular coil and a solenoid when each is carrying a current
when is there a force on a charged particle
there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field
explain why there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field
The movement of the charged particle is a current so it produces a magnetic field. This magnetic field interacts with the permanent magnetic field to create a force. The force is perpendicular to the direction of motion and the permanent magnetic field.
A force is exerted on a current-carrying wire in a magnetic field, how is this effect applied in dc electric motors
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.
A force is exerted on a current-carrying wire in a magnetic field, how is this 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.
use the left-hand rule to predict the direction of the resulting force when a wire carries a current perpendicular to a magnetic field
what does each finger mean
Fleming’s left hand rule.
Thumb: force
First finger: Magnetic Field
Second finger: Current
in FLHR, if current is revered or magnetic field is reversed, then force is _____________
reversed
in FLHR, if current is increased or magnetic field is increased, then force is _____________
increased
how to increase the turning effect (motor)
● increasing the current
● using a stronger magnetic field
● increasing the number of turns on the coil
what does a split ring commutator do
A split ring commutator is used to ensure that the direction that the current flows in the coil
reverses every half turn.
