Electromagnetism - Topic 3 Flashcards
How many poles do magnets have and what are they called?
2 + north and south
Opposite poles ______ each other?
Attract
Like poles _____ each other?
Repel
What way do the magnetic fields attract?
Out of north and into south
Lines relative spacing closer have?
Stronger magnetic fields
Lines relative spacing further have?
Weaker magnetic fields
What is a magnetic field?
The region around a magnet in which another magnet will experience a force?
What should field lines always be drawn with?
Arows going into south and out of north
(Kinda a repeat?)
What is a permanent magnet?
Simple:
A magnet that is always on and can’t be turned off
Annoying:
A permanent magnet is often made from a magnetic metal such as steel. It will always exert a force on other magnets and produces its own magnetic field
What are some advantages of permanent magnets?
They are relatively cheap to buy
They don’t generate heat
No power supply is needed to use them
What are some disadvantages of permanent magnets?
They magnetic field can not be turned on and off and just stays on all the time
The magnetic field of the magnet is set by the type of metal that it’s made from
They can lose their magnetic properties if exposed to high temperatures or large impacts
Describe a few uses for permanent magnets
Fridge magnets - for decoration around house
Hard disk drives - for storing information on disks
Headphones & loudspeakers - making vibrations to produce sound
Cathode ray tubes - to bend and focus an electron beam
What is an electromagnet?
An electromagnet is when an electric current flows in a wire, and creates a magnetic field around the wire and this effect can be used to make an electromagnet
What is in an electromagnet?
An iron nail
A cell
A coil of insulated wire
A switch
What can make an electromagnet stronger?
Wrapping the coil of wire around a piece of iron
(eg. A Nail)
Adding more turns to the coil of wire on the iron nail
Increasing the voltage (and therefore current) going through the coil
What are some advantages of electromagnets?
They can be turned on and off
The strength of their magnetic field can be changed
They can be 20 times stronger than the strongest permanent magnets
What are some disadvantages of electromagnets?
A battery supply is needed to use them
They are vulnerable to power failures
There is a limit to how much current can be passed safely through the wire because the resistance of the wire causes heating
Describe some uses of electromagnets?
Picking up scrap metal - piling up cars and scrap metal
Electric bell - to make a ring noise repeatedly
What are relay switches?
They are a switch used to control a high voltage circuit using a safe low voltage circuit
What does a relay switch consist of?
An electromagnet next to a switch
It looks like: a big box dashed around and in it is a switch / line with separation of a open line
on the right and a box / electromagnet on the left
What happens in a relay switch?
When a current is passed through the electromagnet it causes the switch to close and completes the curcuit
Insuring that it is safe when a there is a high voltage
What is an electric motor and how does it work?
A simple DC monitor usually comprises of two permanent magnets and an electromagnet,
The two permanent magnets are held so that the North Pole is the one faces the South Pole of the other magnet
The coil of wire is mounted in the gap between the two magnets
When a current flows through the coil a force is exerted on the coil causing it to spin
Name a few things that have motors in them?
Household items like…
Electric fans, electric toothbrushes, fridges, microwaves, washing machines, hoovers, and computers
What are super magnets?
Super magnets, such as neodymium magnets are the stringed type of permanent magnets that exist
Name a super magnet?
Neodymium magnets
Where can super-magnets be found?
They can be found in…
MRI machines,
computer hard drives,
electric and hybrid motors,
audio speakers,
electric guitars,
and race car enguines
What is an advantage of super magnets?
They are cheap and widely available
As well as the fact they can be made smaller and lighter than other magnets
What are transformers?
Once energy has been generated it needs to be transported from the power station or generator to consumer homes
This is done by using a system of pylons and cables called the national grid
What is the national grid?
A system of pylons and cables that go through the process of
power stations,
step up transformers,
high voltage transmission lines,
step down transformers,
then our homes
To keep the voltages safe and waste less energy
What are the transformers that increase the voltage and decrease it called?
Step up transformers and step down transformers
What does a transformer have?
Two coils of wire,
A primary coil and secondary coil,
Wrapped around soft iron core
What does a step up transformer have more of in comparison to a step down?
Wire Turns
What is the formula for Ns, Np, Vs, and Vp
Ns/Np = Vs/Vp
To do the sum you times the opposites to each other then divide the numbers your left with after time zing the others together
What is left always in a transformer sum?
The primary one
What is electrical power?
The electrical power is how much energy is used up by an appliance each second
What is the sum for electrical power?
P = E/t
P = watts
E = joules
t = seconds
What is the formula to calculate efficiency?
% efficiency =
useful energy output / energy output x 100
Measured in joules
What is energy?
Something that can’t be destroyed and exist to power things
(not from the notes could be missing smn)
