Magnetic Fields Flashcards
What are the 3 rules when drawing magnetic patterns?
- like poles repel
- unlike poles attract
- field lines from north to south
How are magnetic fields produces in electric circuits?
moving charged particles within a wire
When are magnetic field lines concentric?
long straight current carrying conductors
What do magnetic field lines of a solenoid resemble?
magnetic field lines of a bar magnet
What are the magnetic field lines of a solenoid?
uniform field with a solenoid core
What is magnetic flux density?
strength of the magnetic field
How is Newton’s third law applied to current carrying conductors?
wire and magnet experience equal and opposite forces
Within Flemming’s left hand rule which fingers represent which component?
- thumb: motion (up/down)
- index: field (N to S)
- middle: current (direction)
What is the SI unit of magnetic flux density?
tesla (T)
When does does magnetic flux density equal 1?
when a wire carrying a current of 1A placed perpendicular to the magnetic field experiences a force of 1N per metre of its length
Why do charged particles in magnetic fields move in a circular path?
because magnetic force is perpendicular to velocity
Why is no work done when the particle moves in a circular path?
force has no component in direction travel so velocity remains constant
What is the centripetal force when a particle moves in a circular path?
BQV
What is a velocity selector?
device used in instruments such as mass spectrometer to select charged particles of a specific speed
Define magnetic flux:
product of the component of magnetic flux density perpendicular to the area
Define magnetic flux linkage:
product of the number of turns in coil N and magnetic flux
What units do magnetic flux and magnetic flux linkage use?
Weber (W)
What is Faraday’s law?
the magnitude of the induced emf is directly proportional to the rate of change of magnetic flux linkage
What is Lenz’s law?
the direction of the induces emf or current is always such to oppose the charge producing it
How does an AC generator work?
a coil is rotated at a steady speed in a magnetic field
How does magnetic flux linking the coil in an AC generator vary?
sinusoidally
What is the negative gradient of a flux linkage against time graph equal to?
EMF
What is supplied to the primary input coil of a transfprmer?
alternating current
What does passing alternating current through a transformer cause?
varying magnetic flux in the soft iron core
What does the iron core of a transformer ensure?
no magnetic flux is lost between the primary and secondary coil
In accordance to Faraday’s law what is produced across the ends of a secondary coil in a transformer?
varying emf
What are transformers used for?
to step up and step down voltages
What is equal in a 100% efficient transformer?
output power and input power
