P2- Topic 7- Magnetism and Electromagnetism Flashcards
At which part of a magnet are the magnetic forces
strongest?
The poles of the magnet.
What happens when two magnets are brought close
to each other
They exert a force on each other
What type of force is exerted if two like poles of a
magnet are brought near each other?
A repulsive, non-contact force.
What type of force is exerted if two unlike
poles of a magnet are brought near each
other?
An attractive, non-contact force
What is the difference between a permanent magnet and an induced magnet? 2
● A permanent magnet produces its own
magnetic field
● An induced magnet becomes magnetic
when placed in a magnetic field
What type of force does induced
magnetism always cause?
A force of attraction
What happens when an induced magnet is removed
from a magnetic field?
The induced magnet loses most/all of its
magnetism.
What is a magnetic field?
The region around a magnet where a force acts on another magnet
or on a magnetic material (iron, steel, cobalt and nickel)
Give four examples of magnetic materials. 4
- Iron
- Steel
- Cobalt
- Nickel
What can always be said about the force between a
magnet and a magnetic material?
The force between a magnet and a magnetic material is always one
of attraction
How does the strength of a magnetic field alter as you move further away from
the magnet producing it?
The magnetic field strength decreases
the further you move away
In what direction does a magnetic field point? 2
● In the direction that a north pole would
experience a force if placed in the field
● From the north seeking pole to the
south seeking pole of a magnet
What does a magnetic compass contain?
A small bar magnet that points in the direction of the Earth’s magnetic field
describe how to plot the magnetic field pattern of a magnet using a compass 4
- place the plotting compass near the magnet on a piece of paper.
- mark the direction the compass needle points.
- move the plotting compass to many different positions in the magnetic field, marking the needle direction each time.
- join the points to show the field line
what do lines close together on a magnetic field line pattern
where the lines are close together it shows where the field is strongest
strongest part of the field are at the poles of the magnet
how is the core of the earth magnetic 2
When a plotting compass is placed in the Earth’s magnetic field, the north pole of the compass will line up with the Earth’s magnetic field lines and point to magnetic south
The core is magnetic, and creates a large magnetic field around
the Earth
What is produced when current flows through a
conducting wire?
A magnetic field is produced around the
wire
What determines the strength of the magnetic field around a current-carrying wire? 2
The magnitude of the current flowing through the wire
● The distance from the wire
What is a solenoid?
A coil of wire which when current passes
through creates a strong magnetic field
Describe the magnetic field found inside a solenoid
Strong and uniform
What is an electromagnet?
a solenoid with an
iron core.
describe right hand grip rule 2
thumb point in the direction of the current
other fingers give the direction of the magnetic field
what dictates the strength if a magnetic field 2
greater current = stronger magnetic field
greater distance from wire= weaker field
why does adding the iron core increases the strength of the magnetic field
it is easier for magnetic field lines to pass through than air
factors that affect the strength of the electromagnet
size of the current length cross sectional area number of turns (coils) using a soft iron core
What is the motor effect?
When a force is exerted between a
magnetic field and a current-carrying
conductor placed in that field
What rule is used to determine the force
experienced due to the motor effect?
Fleming’s Left-Hand Rule
describe Fleming’s Left-Hand Rule
thumb= direction of force
1st finger= direction of magnetic field
2nd finger= points in direction of current flow in the conductor
What factors affect the size of
the force on a current-carrying wire in a magnetic field? 2
The magnitude of the current flowing
through the conductor
● The strength of the magnetic field that
the conductor is placed in
If the direction of current in a current-carrying wire placed in a uniform
magnetic field is reversed, what happens to the force?
The direction of the force is reversed.
If the strength of the current in a current-carrying wire placed in a uniform magnetic field is increased, what happens to the force?
The strength of the force is increased.
What criteria must be met for the equation linking
force, magnetic flux density, current and length to
work ?
The conductor must be at right-angles to 90⁰
the magnetic field it is placed in
What is the unit used for magnetic flux density?
Tesla, T
electromagnetic devices
4.7.2.3 flash 2.29
How does an electric motor work?3
● A coil of wire, carrying a current, is placed
in a magnetic field
● The forces on the two sides perpendicular
to the field experience forces in opposite
directions
● This causes a rotational effect
how may another way electric motors work 6
- permanent Magnets lie in fixed positions
- In between, a coil of current-carrying wire lies on an axis
o Force on one side moves that side up
o Force on the other side (where current is flowing in opposite direction) moves down
o This can be verified using Fleming’s Left Hand Rule
- Hence it rotates
How do loudspeakers make use of the motor effect? 2
The motor effect is used to convert variations in the current of an electrical
circuit
into the pressure variations which produce audible sound.
Explain how a loudspeaker works 3
● A cone with a wire wrapped around it is connected to an a.c power supply and is placed in a permanent magnetic field
● When current flows through the wire, it creates a second magnetic field, which interacts with the
permanent field
● This produces a force which causes the cone to vibrate
How is the pitch of the sound from a loudspeaker
changed? 2
● The frequency of the a.c current is altered
● This creates a different frequency of vibration in the cone
What happens when an electrical conductor moves
relative to a magnetic field?
A potential difference is induced across the ends of the conductor.
What happens to an electrical conductor
when there is a change to the magnetic field that it is placed in?
A potential difference is induced across the ends of the conductor
What is the requirement for an induced potential difference to cause a current flow?
The conductor must form a closed loop or be part of a complete circuit.
What can be said about the direction of the magnetic field produced by an induced current?
● The direction of the field is such that it opposes the change that induced the
current
● This change is either the movement of the conductor or a change to the field
What are two ways that the generator
effect is used to generate different types
of current? 2
● In an alternator to produce
alternating-current
● In a dynamo to produce direct-current
a.c & d.c
what is the generator effect
A potential difference or voltage is needed to make an electric current flow in a circuit.
electromagnetic induction = generator effect
How does a microphone use the generator effect?
● It converts the pressure variations in
sound waves into alternating current in
a circuit
Describe the makeup of a basic transformer
A primary coil and a secondary coil of
wire wrapped around an iron core.
Why is iron used as the core for a transformer?
It is easily magnetised.
Why must the current flowing through the
primary coil of a transformer be alternating? 3
For current to be induced in the secondary
coil, the magnetic field in the core must be
continuously changing
● For the magnetic field to be changing, the
current in the primary coil must be alternating
What can be said about the electrical power input and output of a 100% efficient transformer? (
The electrical power input is equal to the
electrical power output.
