Electromagnetic Induction Flashcards
What is an Alternating current
Current that repeatedly changes direction
What is an electromagnet
A soft iron core wrapped in a wire. When current flows through the wire it becomes magnetic
Cutting field lines induces a……………
Voltage
Describe how inducing a voltage into a wire works
When a conductor cuts magnetic field lines, a voltage is induced. This will induce a current if it is in a complete circuit
Maximum voltage is achieved if the conductor moves perpendicular to the field
The direction of the voltage depends on the direction of motion
Cut the lines faster = larger current
What is important about the direction of motion and the direction of the magnetic field in relation to each other
Perpendicular
How do you increase the induced voltage in a wire
Rate of cutting the field lines must increase :
Move the wires faster
Stronger magnets used
More turns on the coil of wire
Describe and explain how generators work
When the col spins it cuts the magnetic field lines
This induces a voltage in the wires
To increase the voltage:
- Spin the coil faster
- Have more turns on the coil
- Use stronger magnets
The slip rings prevent the wires from tangling
How does a transformer work
An alternating current in the primary coil induces a changing magnetic field in the core
This cuts through the secondary coil inducing a voltage in it
The ratio for the number of tuns =
The ratio of the voltages
Np/Ns = Vp/Vs
P = primary S = secondary
Give the equation for transformers
Input voltage
——————- =
Output voltage
Number of tuns on the secondary coil
Describe the energy efficiency in Transformers
Always assume a transformer is 100% efficient
Then we can use the equation P(in) = P(out)
Ip x Vp = Is x Iv
What is the difference between a step down transformer and a step up one
Step down decreases voltage to make it safe but increases current to a reasonable level. Used to transfer electricity between transmission cables to your house
Step up transformers doe the opposite
In the national grid, why do we increase the voltage from 30,000 v to 400,000 v and decrease the current
Much thicker wires would be needed otherwise to cope with the heat (costing more) and more likely to fall down in bad weather
Heat means loosing energy
Electricity is transmitted through the national grid at low………….. and high…………….
Currents
Voltages
What is the national grid
Network of wires and cables that carry electrical energy from power stations to consumers across the UK
