6. Magnetism And Electromagnetism Flashcards
(15 cards)
What are the uses of step-up and step-down transformers?
in the large scale generation and transmission of electrical energy
In the national grid (the system which delivers electricity around the country) transformers are used.
Because the wires are long there is more resistance, so a high current will cause a lot of heat; which is dangerous and looses a lot of energy.
When electricity leaves a power plant, a step up transformer is used, this means the voltage is high, but the current is low.
When electricity reaches a home or business it is stepped down to make it useful in appliances that we use, the wires are shorter so less of a danger is presented by this.
What is the relationship between input(primary) and output(secondary) voltages, and the turns ratio for a transformer?
primary voltage/ secondary voltage = primary turns/ secondary turns
Vp/Vs = Np/Ns
What is a transformer, and what does it do?
What is a transformer made of? Why is it made of this?
A transformer is used to change the current and voltage of electricity.
A current carrying wire is wrapped round one side of a transformer, another wire is wrapped round the other. There will be the same amount of power on both sides, but one will have a higher voltage and lower current the other a lower voltage and a higher current.
The transformer is made of iron, this is because it is a soft metal and can be turned on and off as a magnet: the current from the first wire induces a magnetic field in the transformer, this then induces a current in the second wire.
More coils causes more higher voltage (and lower current.) So if the second side has more turns of wire wrapped round the transformer it will step the current up (step up transformer.) If the second side has less turns, the voltage will be stepped down (step down transformer.)
Describe the generation of electricity by the rotation of a magnet within a coil of wire and a coil of wire within a magnetic field
Describe the factors which affect the size of the induced voltage.
rotate a magnet in a coil of wire and there will be a current induced, the same is true for rotating a coil of wire in a magnetic field.
Factors that increase the electricity generated include: strength of magnetic field; number of coils in wire; speed of rotations.
What happens if you move a wire back and forth across a magnetic field?
What happens if you move a magnet back and forth through a coil of wire?
A voltage will be induced!
(Same answer for both)
If you increase the magnetic field strength, quicken the movement or increase the coils of wire you can increase the voltage induced!
Describe how the force on a current-carrying conductor in a magnetic field increases with the strength of the field and with the current.
A wire in a magnetic field:
- if you increase the current there will be more force on the wire
- if you increase the strength of the magnetic field there will be more force on the wire.
A force is exerted on a current-carrying wire in a magnetic field.
How is this effect applied in simple d.c electric motors and loudspeakers?
In a DC motor, there is a wire in a magnetic field. The force it experiences turns it around, this turns a ‘split ring commutator’ this basically is where charge goes from ‘brushes’ into the wires.
In a loud speaker, a coil is in a magnetic field. When a current is run through it the wire will experience a force that pushes it away from the field, this in turn pushes a cone which makes the sound. Whatever frequency the AC current is at, the coil will move at that frequency, making a note of a certain pitch.
What happens to a charged particle when it moves in a magnetic field? (As long as it’s motion is not parallel to the field)
if something with a charge is moving across a magnetic field, it will experience a force from the field.
(The charged particle experiences a force)
Describe the construction of electromagnets
A piece of wire is wrapped around a soft magnetic material. When there is a current in the wire, a magnetic field is induced in the metal.
What does an electric current in a conductor produce around it?
A magnetic field!
If you run an electric current through anything that conducts (e.g. a wire) a magnetic field will be produced around it!
describe how to use two permanent magnets to produce a uniform magnetic field pattern.
If you put two bar magnets together with their north and south touching, then they will form the same magnetic field as if there were one bar magnet.
‘hold two opposite poles close to each other so that they attract as this makes a uniform magnetic field’
describe experiments to investigate the magnetic field pattern for a permanent bar magnet and that between two bar magnets
To track field lines you can use iron filings, which are magnetic materials, which will line up along the magnetic field.
you can use compasses which will show that the lines go from north to south.
How is magnetism induced in some (non-magnetic) materials when they are placed in a magnetic field?
Some materials that are not magnetic can become one when they are in a magnetic field. This is because the magnetic field encourages its electrons to align and form poles. This can happen in iron (and steel), cobalt and nickel.
What is the definition of a ‘magnetic field line’?
Magnetic field lines represent the shape and direction of a magnetic field.
Its important to realise that these lines only represent the field and that the spaces in-between the lines are not in fact spaces in the field, a field is also three dimensional, so the lines just give an idea.
What are the properties of…
Magnetic hard materials:
Magnetic soft materials:
Magnetic hard materials: retain their magnetic properties for a long period of time/ permanently. They are hard to demagnetise.
Magnetic soft materials: loose their magnetic properties almost as soon as they leave a magnetic field.
