SP13a - Explain how a loop of wire can gain an induced current using a magnet.
- A magnet has a magnetic field around it.
- Once it moves throughout the wire, the field induces a P.d. in the wire which creates a magnetic field opposite to original change.
SP13a - How does an alternator work?
- A coil of wire wrapped around an iron core is rotated inside a magnetic field
- Wires from the coil are connected to slip rings on the axle of the coil
- The slip rings make electrical contact through carbon brushes
- This produces an alternating current
SP13a - How does a dynamo work?
Same concept as an alternator except:
- The wires are connected to a split ring commutator
- The commutator is connected to the carbon brushes
- Every half-turn the connections are swapped
- Thus, this produces a direct current
SP13a - How do microphones work?
- (The opposite to loudspeakers)
- Sound waves cause vibrations in air pressure
- The pressure causes a diaphragm to move back and forth
- The diaphragm moves a coil of wire back and forth
- This causes the coil which is wrapped around a permanent magnet to gain an induced voltage and current
- The amplitude of the wave affects the volume
- The frequency affects the pitch
- Converting sound energy into electrical energy
SP13a - How do loudspeakers work?
- (The opposite to microphones)
- An a.c. voltage passes througha coil
- This moves the coil along a permanent magnet
- The coil hits the diaphram causing it to vibrate
- This creates soundwaves
- The higher the current, the larger the frequency and amplitude
- And so the volume and pitch is higher
- Converting electrical energy into sound energy
SP13b - What is the national grid?
The system that connects power stations to homes to provide electricity nationally
SP13b - What are transformers, both step-up and step-down?
Transformers are (not robots in disguise) devices that alter the voltage and current of electricity.
- SU increase voltage; decrease current
- SD decrease voltage; increase current
SP13b - Describe the process of transferring energy from power stations to houses and factories.
- Electricity is generated at the power station (11kV)
- Stepped up (400kV) for transmission lines
- Stepped down (33kV) Where some is used in large factories
- Some is stepped down further (11kV) for small factories
- Rest is stepped down instead (230V) to be used in houses shops etc.
SP13b - Why is electricity stepped up before transmission?
- A higher voltage means a lower current.
- A higher current would mean a higher power loss (P = I²xR).
- So the lowest possible current is attained so that the least amount of energy is lost by heating.
- Low resistance wires are also used (thicker).
SP13b - What is the structure of a transformer?
A primary coil (connected to an a.c supply) and a secondary coil with differing amounts of turns, wrapped around an iron core.
SP13b - How do transformers work?
- Changing a.c current supplied
- This produces a changing magnetic field in primary coil
- The iron core is induced and carries this changing magnetic field
- This creates a changing magnetic field in the secondary coil
- This induces a changing a.c voltage in the wires connected to the secondary coil.
SP13c - What is the voltage current transformer equation and what does it assume?
V(p) x I(p) = V(s) x I(s)
[assuming that the transformer is 100% efficient]
SP13b - Which equation links voltage and turns across coils?
V(p)/V(s) = T(p)/T(s)
V = Voltage across coil
T = Turns in coil
SP13c - What are the equations for power and energy?