Electromagnetism Flashcards
What happens when electricity is passed through a coil of wire?
The coil behaves like a magnet and has a magnetic field around it- this is an electromagnet.
What are the three ways to make an electromagnet stronger?
- wrap the coil of wire around an iron core
- increase the number of coils
- increase the size of the current
What is the importance of an electromagnet?
- It can be easily turned on and off
- Therefore electromagnets can be used in scrapyards and as switches in electrical devices.
Investigations to investigate the two other factors that affect the strength of an electromagnet are
1, Investigate how the number of coils affects the number of paper clips attracted to the electromagnet-keep the current same in this experiment
2, Investigate how the size of the current affects the number of paper clips attracted to the electromagnet- keep the number of coils same in this experiment
Flemings Left hand rule
1, thuMb- Motion
2, First finger- magnetic Field
3, seCond finger- Current
They are all at right angles to each other.
How can the direction of the force acting on a wire in an electromagnetic field be reversed?
- reversing the current
- reversing the magnetic field
What is an electric motor?
It is a device that converts electrical energy into mechanical energy to produce a turning effect.
What are most motors powered using?
Direct current, which is produced by cells and batteries.
What are most motors powered using?
Direct current, which is produced by cells and batteries.
What do motors powered by mains electricity use?
alternating current
Motors powered by mains electricity use
electromagnets rather than permanent magnets
What are the ends of a magnet called?
Poles
What two poles does a magnet have?
A north and south pole
What is the law of magnetism?
When two magnets are held close together, there will be an attractive or repulsive force between the magnets depending on how they are arranged.
Two like poles
repel each other
Two unlike poles
attract each other
The attraction or repulsion between two magnetic poles is an example of what force?
A non-contact force
What metals in the periodic table are magnetic?
Iron, nickel and cobalt
Steel
It is an allow that contains iron so is also magnetic
Are magnetic materials always attracted to the magnet?
Yes, regardless of the pole which is held close to it.
How do you test whether a material is magnetic?
It should be brought close to a known magnet.
- if it can be repelled by the known magnet then the material itself is a magnet
- If it can only be attracted and not repelled then it is a magnetic material
What are the two types of magnets?
Permanent and induced magnets
Permanent magnets
- They are made out of permanent magnetic materials eg: steel
- A permanent magnet will produce its own magnetic field. It will not lose its magnetism.
Induced magnets
-when a magnetic material is placed in a magnetic field,the material can be temporarily turned into a magnet
What happens when magnetism is induced on a material?
- One end of the material will become a north pole
- The other end will become a south pole
Magnetic materials will always be attracted to a
permanent magnet
Since a magnetic material is always attracted to a permanent magnet, what does this mean?
This means that the end of the material closest to the magnet will have the opposite pole to the magnets pole closest to the material.
What happens when a magnetic material is removed from the magnetic field?
It will lose all/most of its magnetism quickly.
What are all magnets surrounded by?
A magnetic field
What is the definition of a magnetic field?
The region around a magnet where a force acts on another magnet or on a magnetic material (such as iron, steel, cobalt and nickel).
What are magnetic field lines used for?
They are used to represent the strength and direction of a magnetic field.
How is the direction of a magnetic field shown?
Using arrows.
How is the strength of a magnetic field shown by?
The spacing of the magnetic field lines
If the magnetic field lines are close together,
the magnetic field will be strong
If the magnetic field lines are far apart,
the magnetic field will be weak
What are the rules which should be followed when drawing magnetic field lines?
- They always go from north to south (indicated by an arrow midway along the line)
- they must never touch or cross other field lines
What is the magnetic field like around a bar magnet?
- the magnetic field is strongest at the poles
- This is where the magnetic field lines are closest together
- the magnetic field becomes weaker as the distance from the magnet increases
- This is because the magnetic field lines are getting further apart.
What can an attractive force be experienced between?
- The opposite poles of two different permanent magnets (due to the law of magnetism)
- A magnet and a magnetic material (due to induced magnetism).
Where is a uniform magnetic field produced?
In the gaps between opposite poles (it is not uniform outside that gap)
What is a uniform magnetic field?
One that has the same strength and direction at all points
How do you show that a uniform magnetic field has the same strength at all points?
There must be equal spacing (same distance apart) between all magnetic field lines.
How do you show that a uniform magnetic field acts at the same direction at all points?
There must be an arrow on each magnetic field gong from the north pole to the south pole.
A magnetic field is a
non-contact force. It is a region around a magnet where a force is experienced. It is a vector quantity (Nā>S)- out of north into south
How does a motor work?
- the sides of the coal (parallel to the magnet) experience a force in opposite directions
- the forces cause moments that act in the same direction/ the two halves of the commutator swap from one br
F= BIL
B- magnetic field density- Teslas
I - current A
L- length m
How do we know that the core of the Earth is magnetic?
A magnetic compass will always point north.
What is produced when a current flows through a conducting wire?
A magnetic field is produced around the wire.
How can the shape and the direction of a magnetic field be be investigated?
By using plotting compasses.
What is a magnetic field made up of?
concentric circles.
What does a circular field pattern indicate?
It indicates that a magnetic field around a current-carrying wire has no poles.
As the distance from the wire increases, what happens to concentric circles of a magnetic field?
They get further apart.
What do the concentric circles show about the magnetic field?
The magnetic field is strongest closest to the wire and gets weaker as the distance from the wire increases.
What can be used to work out the direction of the magnetic field?
The right hand thumb rule
Right hand thumb rule
Thumb- points along the direction of the current
other fingers give the direction of the field
What will reverse the direction of the magnetic field (right-hand thumb rule)
Reversing the direction in which the current flows through the wire
What does a circle with a dot in the centre show?
Current is flowing out of the plane.
What does a circle with a cross in the centre show?
Current is flowing into the plane.
When will there be no magnetic field?
If there is no current flowing through the conductor.
What will increase the strength of the magnetic field?
Increasing the amount of current flowing through the wire.
When does the motor effect occur?
It occurs when a wire with current flowing through it is placed in a magnetic field and experiences a force.
What is the result of two magnetic fields?
- One is produced around the wire due to the current flowing through it
- the second is the magnetic field into which the wire is placed eg: between two magnets.
