Magnetism, the motor effect, and electromagnetic induction Flashcards
A bar magnet is an example of a _________ magnet.
Permanent
When a piece of magnetic material is in a magnetic field it becomes a magnet itself e.g. when one paperclip attracts the next paperclip. This is called an ________ magnet.
Induced
List the three magnetic elements.
Iron, nickel and cobalt
What is a magnetic field?
The area around a magnet where it can attract magnetic materials
Magnetic field lines never cross, and always include arrows that point from ____ to ____
North to South
The shape of a magnetic field can be found using a:
Plotting compass
What does it tell you if magnetic field lines are close together?
The field is strong
Where are the field lines closest together around a bar magnet?
At the poles
Describe the field lines in a uniform field
Parallel, equidistant, arrows pointing from N to S
Which rule do you use to work out the direction of the magnetic field around a current carrying wire?
The right hand grip rule
What kind of magnet is created when you pass a current through a coil of wire?
An electromagnet
Describe the shape of the magnetic field around a solenoid
similar to that of a bar magnet, almost uniform and strong inside the coil, weaker above and below the coil
How can you increase the strength of an electromagnet?
More Coils, larger Current, or use a magnetic Core e.g. Iron
What do the thumb, fore finger and second finger represent in Flemming’s left hand rule?
Thumb = Force
fore finger = Magnetic Field
second finger = Current
What is the equation that gives the strength of the force on a current carrying wire within a magnetic field?
F = B x I x L
Force(N) = Magnetic field strength (T) x Current (A) x length (m)
What is the name of the effect that makes a wire ‘jump’ when it has a current passing through it and is placed within a magnetic field?
The motor effect
What is the unit for Magnetic field strength (aka magnetic flux density)?
Tesla (T)
What letter is used to represent magnetic flux density, or magnetic field strength?
B
What does a step up transformer do to the voltage of an electricity supply?
Increases the voltage of an electricity supply
What kind of current is needed for a transformer to work?
Alternating current
In a step down transformer, where is there an induced voltage?
In all transformers there is an induced voltage in the secondary coil
A step down transformer has (more/fewer) turns on the secondary coil compared to the primary coil
Fewer
Calculate the missing value. Is this a step up or step down transformer? (VpIp = VsIs)
Vp = 500V
Ip = ?
Vs = 5V
Is = 2A
Step down.
Ip = 0.02A
In order for energy to be conserved, what must always be the same in the primary and secondary coils of a transformer?
Power (or rate of energy transfer).
P = I V
Where are transformers found in the national grid, and are they step up or step down transformers?
Step up transformers are used as the supply leaves the power station. Step down transformers are found just before the supply goes to factories, and again before the supply goes to homes.
Why are transformers needed in the national grid?
Transformers are used to step up the voltage to 400kV in order to reduce the current. Lower current reduces energy dissipated through heat.
How can you change the amount of potential difference induced?
Increase the number of turns in the coil, move the magnet faster or use a stronger magnet.
How can you change the direction of an induced voltage?
Change the direction of motion or reverse the magnetic field.
