Magnetism Flashcards
What is magnetism?
The force exerted by magnets when they attract or repel each other
What is electricity?
The movement of electrons
What are free electrons?
Electrons that have separated from their atoms
How can you tell which direction a magnetic field is going?
The right-hand thumb rule:
Thumb points in direction of current direction
Other fingers point in direction of magnetic field lines
What is a solenoid?
A wire made into a coil that carries electric current
What are the two factors that the strength of a magnetic field in a coil depend on?
The current
the number of turns on the coil
What happens when a solenoid has a ferromagnetic rod (core)?
The magnetic field lines are enhanced
What is magnetic flux?
The total magnetic field passing through an area
What are the symbol and SI unit for magnetic flux?
Φ
Wb (Weber)
What is permeability?
What is its symbol?
What is its unit?
How easy magnetic lines of force can pass through a material
μ (mu)
H/m (henries per metre)
What is mmf?
Magnetomotive force (mmf) is the force that pushes magnetism
How is mmf calculated? What is its unit?
Fm = N x I
mmf = no. turns in coil x current
At (ampere turns)
What is the equation for magnetic field strength? What is its unit?
H = Fm / L
magnetic field strength = mmf / length
At/m (ampere turns per metre)
What is reluctance?
The ability to oppose the floe of magnrtic flux (like resistance in a circuit)
How is reluctance calculated? What is its unit?
S = L / (μ x A)
reluctance = length / (permeability x cross-sectional area)
At/Wb (ampere turns per weber)
How is permeability calculated?
μ = μ0 x μr
permeability = permeability of free space x relative permeability
What does Hopkinson’s Law state?
(In magnetic circuits:) Fm = Φ x S
mmf = magnetic flux x reluctance
What is saturation?
No matter how high the mmf gets in a magnetic circuit, the flux will level out
What is flux density? How is it calculated? What is its unit?
How much flux per unit area
B = μ x H
flux density = permeability x magnetic field strength
T (Tesla)
What does the B-H curve show?
Flux density against magnetic field strength on a graph
What do inductors do?
Use current to create an emf
What is an induced current?
Current generated in a wire due to a changing magnetic field
What are the ferromagnetic metals?
Iron
Nickel
Cobalt
Steel
What does magnetic screening do?
Protect electric circuits/ devices from emfs
