Magnets, Electromagnet Induction, Electric Motors And Transformers Flashcards
What materials experience magnetic properties
Iron, steel, nickel and cobalt
What is the region around a magnet called
A magnetic field
Ends of magnets
These are called poles, north and south and the magnetic fields are strongest here
Law of attraction
Same poles repel, opposite poles repel
Repelling magnets
There is an area in the middle of the poles where the fields cancel wach other out and there is no overall magnetic field
Attracting magnets
How do you make an electromagent
When a current flows through a wire, a weak magnetic field is created around a wire
How to change the strength of the magnetic field line around a current carrying wire
You can increase the strength by
- Increasing the current in the wire
- Wrapping the wire into a coil (a solenoid)
Magnetic field lines around a solenoid
They are the same as around a bar magnet
How can you increase the strength of the magnetic field around the solenoid
- Increase the current
- Increase the number of turns (amount of spins in the coil)
- Wrapping the solenoid around a magnetically soft core such as iron, this is called an electromagnet
Using electromagnets
- The electric bell
- The relay switch
- Circuit breakers
The electric bell
Switch closed, circuit complete
Electric current flows through
Soft iron core is magnetised
This attracts the steel armature (bar)and the wire which is atttached to it
This pulls the hammer, which hits bell and creates a sound
The circuit is now broken though so the electromagnet is demagnetised and as the wire is springy, it springs back
The process repeats
The relay switch
Switch is closed and circuit is complete
Low current passes through and soft iron core is electromagnetised
This means the iron arm is attracted to the magnet and as it moves it pushes the contacts together
This completes the second circuit and current passes through it, powering the motor which begins to spin
When the switch is opened in circuit 1, the iron arm returns to its original position as it is on a spring, breaking circuit 2 and prohibiting the motor from turning
How does the electric motor work
- Electricty put into the circuit
- Left side= upward right side= downward (hand rule) currents are moving in different directions
- Split ring commutator means rotating forces can switch every half turn
- Brushes complete circuit and connect coil to electric supply without prohibiting the split ring commutator to spin
Why are the brushes in an electric motor normally made of carbon or graphite?
They both conduct electricity due to free electrons and they are soft so there is little friction between the bristles and the split ring commutator
Why does the coil spin through a vertical position on an electric motor/why wouldnt it?
It wouldnt because at vertical the forces are equal to the right and left side sono resultant force
However it builds up momentum and the split ring commutator allows it to spin through vertical and then the rotating forces switch
What affects the speed of the motor?
- Friction bewteen brushes and split ring commutator
- Strength of magnets
- Conductivity of wire
What is electromagnetic induction?
When a wire is moved thoguh a magnetic field, it cuts through the flux lines and a potential difference is induced. When the wire is connected to an (a.c) circuit, a current will flow through it
How does electromagnetic differ from the motor effect?
Motor effect= put electricity in and get motion out
Electromagnetic induction= put motion in and get electricty out creates a generator
Why is the current a.c?
When the magnet is stationary inside the solenoid, no current flows as it has to be moving a constantly cutting the field lines
Why is both a negative and positive voltage induced when a magnet is dropped through a coil
Because the potential difference is different a both ends of the coil so there are postive and negative charges
How can you increase the current the generator produces?
- Move the magnet faster
- Use a stronger magnet
- Use a coil with more turns
- Use a coil with a larger cross sectional area
What is the purpose of step up tranformers?
Increase voltage
Decrease current
Decrease heat
Decrease efficiency
Describe how this transformer works
- When an ac current is passed through a wire, it creates a magentic field. This magnetic field created around the primary coil will cut through the secondary coil and induce a current
- More coils = lower current so there is a higher current in the primary coil
- Because P=IV and Pout = Pin, the voltage of the secondary coil will be higher
