Magnetic Fields Flashcards
Magnetic field
A place that will cause a magnetic pole to experience a force
Magnetic flux definition
is a quantity which signifies how much of
a magnetic field passes perpendicularly through some area
The magnetic flux is maximum when…
the magnetic field lines are perpendicular to the coil area
The magnetic flux is minimum when…
the magnetic field lines are parallel to the coil area
Magnetic flux linkage definition
The product of the magnetic flux and the number of
turns of the coil (Wb turns)
The motor effect:
- When a current flows in a wire a magnetic field is produced around the wire
- Increasing the current will increase the strength of the magnetic field produced
- Therefore, if a current carrying wire is placed in a magnetic field it will experience a force
Flemings left hand rule
- Thumb = motion
- First finger = magnetic field
- Second finger = current
Electro magnetic induction
The process in which an e.m.f is induced in a closed
circuit due to changes in magnetic flux (linkage)
Explain how shaking the torch produces an
electric current
- Lines of magnetic flux cut through coil of wire
- Reference to electromagnetic induction
- Therefore is a complete circuit so there is current in the coil
Factors that will increase the induced e.m.f are:
- The speed of the magnet through the coil
- Adding more turns to the coil
- Increasing the strength of the magnet
Alternating voltage
When a coil rotates in a uniform magnetic field, the magnetic flux through the coil will vary as it rotates, this will induce an e.m.f that also varies
A coil in a magnetic field can act as a generator. The coil rotates. Explain how this produces a current in the coil.
- The coil cuts magnetic field lines
- Inducing an emf
- Generating current because there is a closed circuit
Increasing the coil’s frequency of rotation increases:
- The frequency of the alternating voltage
- The amplitude of the alternating voltage
A transformer is made up of:
- A primary coil
- A secondary coil
- An iron core
The primary and secondary coils are wound around the soft iron core. The soft iron core is necessary because it creates flux linkage between the primary and secondary coils
Types of transformers:
- step up transformer (increase voltage)
- step down transformer (decrease voltage)
What is conserved across transformers?
Power and therefore energy
Explain how a lower pd is produced across the
secondary coil in a step down transformer
- Alternating current produced alternating magnetic
flux - Magnetic flux is linked to secondary coil by iron core
- Changing magnetic flux INDUCES emf in secondary
coil - Less turns on secondary coil
Faraday’s law
The magnitude of the induced e.m.f is directly proportional to the rate of change of magnetic flux linkage
Lenz’s law definition
The induced e.m.f is set up in a direction to produce
effects that oppose the change causing it
Lenz’s Law dictates:
-The direction of the e.m.f, and hence the
current, must be set up to oppose the
incoming magnet
-Since a north pole approaches the coil face,
the e.m.f must be set up to create an induced
north pole
-This is because two north poles will repel each
other
Explain how a loudspeaker works:
- An alternating potential difference is applied to coil
- This produces an alternating current in the coil
- Current in coil causes a magnetic field
- Field changes direction with same frequency as AC
- Coil´s field interacts with permanent magnet´s field
- Therefore coil experiences an alternating force
- This causes the cone to vibrate
