6.3 Flashcards
Magnetic field
Region around a permanent magnet or moving charge in which another body with magnetic properties will feel a force
Magnetic field lines
Show the shape of the field and the direction a plotting compass would point at that point
Solenoid
Long coil of current carrying wire
How do we determine the direction of the magnetic field around a current carrying wire?
Right hand rule 👎🏻
Magnetic flux
Product of the flux density B and the area A at right angle to the flux
Measured in Wb
Amount of magnetic field passing through a surface
Magnetic flux density
Strength of the magnetic field
Flux passing perpendicular through an area
Measured in T or Wb m^-2
Weber
Magnetic flux when a magnetic field of magnetic flux density 1 T passes at right angle through an area of one square metre
Fleming’s left hand rule
Shows the direction of the force on a conductor carrying a current in a magnetic field
Force/thumb, field/first finger, current/second finger
(Conventional current)
What is the relationship between the force on a wire and the angle between it and the field
SinA, A=0 they are parallel, no cutting
How does a charge act when moving in a constant magnetic field?
Force acting perpendicular to motion produces circular motion in the particle, no force acting in direction of motion means no increase in speed
How can you change the radius of the circle a charge makes moving in a field?
Increasing speed or mass increases the radius, increasing charge or field strength decreases radius
How do mass spectrometers work?
Ions are fired into uniform magnetic fields, the radius of the circular path the ion follows is directly proportional to its mass
Electromagnetic induction
Process of inducing an emf in a conductor when there is a change in the magnetic flux linkage across the conductor
Induced emf
Emf produced by the electromagnetic induction
Magnetic flux linkage
The product of the magnetic flux through a coil and the number of turns on the coil
Units are weber turns
Faraday’s Law
Magnitude of the induced emf is equal to the rate of change of flux linkage
Lenz’s Law
The direction of any induced emf or induced current is in a direction that opposes the flux linkage that causes it
Search coil
Small, flat coil used to determine the strength of a magnetic field
Generator
Device used to generate electricity in which the work done to turn the coil within the magnetic field is transferred to electrical energy. The rotation of a coil within a magnetic field produces a constantly changing flux linkage and so a constantly changing emf
Alternating current
Electrical current that reverses its direction with a constant frequency
Transformer
Device that can either increase or decrease the size of ac voltage with little power loss
Ratios of transformers
Ns / Np = Vs / Vp = Ip / Is
How do transformers increase efficiency
Iron core centres, that are laminated or made up of lots of thin layers of iron glued together reduce the effects of eddy currents
Why is an iron core used
It has a high magnetic permittivity and concentrates the magnetic field or flux
Why are the coils in a transformer close together
The closer the two coils are, the greater effect a changing magnetic field in the primary coil has on the secondary coil
