Motors, Generators and Transformers Flashcards
Describe how transformers work
- the primary cook produced a magnetic field which stays within the iron core. Nearly all of it passes through the secondary coil.
- due to AC current in the primary coil, the field in the iron core is constantly changing direction
- this rapidly changing magnetic field is then felt by the secondary coil
- the changing field induces and alternating potential difference across the secondary cool called electromagnetic induction
What is the motor effect?
- When a wire carrying a current is placed in a magnetic field it experiences a force.
- this can cause the wire to move
What do like poles do to each other and what to opposite poles do?
- like poles repel each other
- opposite poles attract
Does the iron core carry current?
- no, it only carries magnetic field.
- the soft iron core is purely transferring the changing magnetic field from the primary coil to the secondary coil.
- no electricity flows around the iron core
What does reversing the current or magnetic field do to the direction of the force?
- reverses the direction of the force
What happens when a current flows through a wire?
- a magnetic field is created around the wire
- the field is made up of concentric circles perpendicular to the wire, with the wire in the centre
You can use the Right-Hand Thumb Rule to determine the direction of the magnetic field
What does placing north and south poles of two permanent bar magnets near each other do?
- creates a uniform field between the two magnets.
In a step-up transformer, is the potential difference across the secondary cook greater or less than the p.d. across the primary coil?
And vice versa
- greater
- less
What do the relative number of turns on the two coils determine?
- whether the potential difference induced in the secondary coil is greater or less than the potential difference in the primary
Does the iron core carry current?
- no, it only carries magnetic field.
- the soft iron core is purely transferring the changing magnetic field from the primary coil to the secondary coil.
- no electricity flows around the iron core
What will happen if you move he magnet in the opposite direction, or if the polarity of the magnet is reversed?
The voltage/current will be reversed too.
What is a magnetic field?
A region where magnetic materials experience a force.
Describe how transformers work
- the primary cook produced a magnetic field which stays within the iron core. Nearly all of it passes through the secondary coil.
- due to AC current in the primary coil, the field in the iron core is constantly changing direction
- this rapidly changing magnetic field is then felt by the secondary coil
- the changing field induces and alternating potential difference across the secondary cool called electromagnetic induction
What do magnetic field lines show?
- The size and direction of magnetic fields.
- They always point from north to south
What are switch mode transformers?
- a type of transformer that operate at higher frequencies than traditional transformers
- usually between 50kHz and 200 kHz
- they can be made much lighter and smaller than traditional transformers that work from a 50Hz mains supply
- makes them useful for things like mobile chargers and power supplies such as for laptops
- use very little power when they are switched on but no load is applied
What does a split-ring commutator do?
It swaps the contacts every half turn to keep the motor rotating in the same direction
How do you increase the strength of the magnetic field around a solenoid?
- by adding a magnetically ‘soft’ iron core through the middle of the coil.
- it magnetises and demagnetises very easily
How does the force change with an increase amount of current passing through the conductor
- the force increases
What is the generator effect?
The induction of a potential difference in a wire which is experience a change in magnetic field
What are step-down transformers?
- they step the voltage down
- they have more turns on the primary coil than the secondary coil
What is the transformer equation?
Vp/Vs = np/ns
Explain Fleming’s right-hand rule
The fingers mean the same thing as the left-hand rule for motors, except the second finger means induced voltage or current
How can a wire experience the full force of the motor effect?
- the wire has to be at 90° to the magnetic field
- if it runs along the magnetic field, it won’t experience any force at all
How do you get alternating current?
If you keep the magnet (or the coil) moving backwards and forwards, you produce a voltage that keeps swapping direction
What is direct current?
Current that only flows in one direction
What would happen if you supplied DC to the primary coil?
- you would get nothing out of the secondary. It is not constantly changing so there is no induction.
- you need a changing field to induce a potential difference.
How do generators work to produce AC?
- as you turn the magnetic, the magnetic field through the coil changes. This change in the magnetic field induces a voltage, making current flow in the wire
- when you’ve turned the magnet through a half turn, the direction of the magnetic field through the coil reverses. This reverse the voltage, so current flows in the opposite direction
- if you keep turning the magnetic in the same directions, the voltage will keep reversing every half turn and you will get AC
What happened when a magnet is brought near a magnetic material?
- that material acts as a magnet
- this magnetism has been induced by the original magnet
- the closer the magnet and the magnetic material get, the stronger the induced magnetism will be
Describe a DC generator.
- DC Generators rotate a cool in a magnetic field (or a magnet in a coil) similar to a motor
- as the coil spins, a current is induced in the coil. This current changes every half turn
- DC Generators have a split-ring commutator, so the contacts swap every half turn, keeping the induced current flowing in the same direction
Which four factors affect the size of the induced voltage?
- the strength of the magnet
- the area of the coil
- the number of turns on the coil
- the speed of movement
Describe a DC generator.
- DC Generators rotate a cool in a magnetic field (or a magnet in a coil) similar to a motor
- as the coil spins, a current is induced in the coil. This current changes every half turn
- DC Generators have a split-ring commutator, so the contacts swap every half turn, keeping the induced current flowing in the same direction
Name two transformers and what a basic transformer consists of.
- Step-up transformer and step-down transformer
- they both have two coils, the primary and the secondary, joined with a soft iron core.
What is an electromagnet?
A magnet whose magnetic field can be turned on and off with an electric current.
Describe AC Generators
- Generators rotate a coil in a magnetic field. Construction is similar to a motor
- As a coil or magnet spins, a current is induced in the coil. This current changes direction every half turn.
- AC Generators have slip rings and brushes so the contacts don’t swap every half turn
- Faster revolutions produce not only more peaks but higher overall voltage.
What is the electrical power output equation?
Vp x Ip = Vs x Is
Describe AC Generators
- Generators rotate a coil in a magnetic field. Construction is similar to a motor
- As a coil or magnet spins, a current is induced in the coil. This current changes direction every half turn.
- AC Generators have slip rings and brushes so the contacts don’t swap every half turn
- Faster revolutions produce not only more peaks but higher overall voltage.
What are step-down transformers?
- they step the voltage down
- they have more turns on the primary coil than the secondary coil
What are step-up transformers?
- they step the voltage up
- they have more turns on the secondary coil than the primary coil
What is a could of wire called?
A solenoid
What are step-up transformers?
- they step the voltage up
- they have more turns on the secondary coil than the primary coil
Name two transformers and what a basic transformer consists of.
- Step-up transformer and step-down transformer
- they both have two coils, the primary and the secondary, joined with a soft iron core.
How do you create potential difference in a conductor?
- moving a magnet in a coil of wire
- moving a conductor in a magnetic field
How can you reverse the direction of a motor?
- by swapping the polarity of the direct current supply
- swapping the magnetic poles over
What would happen if you supplied DC to the primary coil?
- you would get nothing out of the secondary. It is not constantly changing so there is no induction.
- you need a changing field to induce a potential difference.
What is a magnetic field inside a solenoid like?
- strong
- uniform
Explain Fleming’s right-hand rule
The fingers mean the same thing as the left-hand rule for motors, except the second finger means induced voltage or current
What do the relative number of turns on the two coils determine?
- whether the potential difference induced in the secondary coil is greater or less than the potential difference in the primary
What happens to the magnitude of the force as the magnetic field increases in strength?
The force increases
What does each finger represent in Fleming’s Left Hand Rule
- First finger: the direction of the field
- Second finger: the direction of the current
- Thumb: direction of the force
In a step-up transformer, is the potential difference across the secondary cook greater or less than the p.d. across the primary coil?
And vice versa
- greater
- less
