Magnetic Fields Flashcards
State Faraday’s Law.
The induced e.m.f. is directly proportional to the rate of change of magnetic flux linkage.
State Lenz’s law.
The direction of induced emf is such as to oppose the change that induces it.
Explain what happens when you move a straight conductor through a magnetic field.
→ electrons experience a force pushing
them to one end of conductor
→ creates an emf across conductor
→ rod obeys Faraday’s law, & flux changes
Describe how a transformer works.
→ a primary coil wrapped around an iron core with alternating p.d. creates an alternating magnetic field
→ this magnetic field induces an EMF in a secondary coil wrapped around core
→ creates a current in the secondary coil
State and explain the feature of transformers designed to minimise eddy currents.
→ laminated core - thin sheets separated by thin layers of insulators
→ current cannot flow through a discontinuous conductor
Explain, in terms of electromagnetic induction, how a transformer may be used to step
down voltage.
- changing primary magnetic field due to alternating voltage
- varying flux links with secondary
- induced emf is proportional to rate of change of flux linkage
- NS < NP so less voltage on secondary
State how eddy currents are produced.
- changing magnetic flux induces emf within core
- this induces loops of currents
- these heat the core & cause energy to be wasted
State two reasons why a transformer may be less than 100% efficient.
- less than 100% flux linkage
- iron losses
Explain how energy loss due to coils heating up can be reduced in a transformer.
→ use low resistance wires
→ e.g thick copper wires
Explain why a magnetically soft material is used for the core of a transformer.
- core is continuously magnetised & demagnetised
- requires energy + heats the core
- ∴ more efficient to use material that is easily magnetised
Explain why a proton travels in a semicircular path in a dee.
→ force due to uniform magnetic field is constant and) at 90º to direction of travel
→ this is the centripetal force
