Topic 11: Electromagnetic induction Flashcards
State Faraday’s law of induction.
The size of the induced emf is proportional to the rate of change of flux linkage
Explain, using Faraday’s law of induction, how a step-down transformer steps down a voltage
- There is a varying current/voltage in the primary coil, producing a varying magnetic field
- This produces a change in flux linkage in the secondary coil
- Therefore, a varying emf is produced in the secondary coil
- The voltage will be stepped down as there are more turns in the primary coil than in the secondary coil
How are energy losses reduced in the core of a practical transformer?
- They have a laminated core which decreases eddy currents
- Therefore, less thermal energy is transferred to the surroundings
What is an eddy current and how do they cause energy dissipation?
- A small current created in the iron core that come from the changing magnetic fields
- The current created moves free electrons within the core causing heating of the core and therefore energy dissipation
State Lenz’s law.
An induced emf acts in the direction such that the current induced opposes the change which caused it.
What is a transformer?
A device that changes high alternating voltage at low current to low alternating voltage at high current, and vice versa
Step-up transformers are used in power stations to increase the voltage at which the electricity is transmitted. Explain why this is done.
- By increasing the voltage, the current would decrease
- High currents cause the wire to heat up and cause energy dissipation
What is the photoelectric effect?
The phenomenon in which electrically charged particles are released from or within a metal when it absorbs electromagnetic radiation.
State what is meant by the work function of a metal.
The minimum energy required to remove an electron from the metal’s surface.
