Magnetism, EM induction and AC Flashcards
Right hand grip rule
Fingers: field
Thumb: current
Force formulas
Force on charge carrying wire
F = B I L sinθ
Force on charged particle
F = B Q v sinθ
Magnetic flux density meaning
Force experienced by a straight current carrying conductor at right angles to that field per unit length and unit current
1 Tesla is…
when a current carrying wire of 1m length with 1A current placed at at a right angle to a magnetic field experiences a force on 1N
Left hand rule
Thumb: force
Index: field
Middle: current
Force goes in opposite direction if electrons are considered instead of current
Centripetal force provided by magnetic force
Fc = Fn
mv²/r = B Q v sinθ
r = m v sinθ / Bq
Hall effect formulas
Vʜ = I B / n q t
I is current
B is magnetic flux density
n is number charge density
q is elementary charge
t is thickness of the waver
Conservation of energy with Hall effect;
lots of formulas
Fe = q E
q is elementary charge
E is electric field strength
W = Fe x d = Vʜ x q
v = E / B
v (velocity of charged particle)
E (electric field strength)
B (magnetic field strength)
E = V / d
E (electric field strength)
V (pd between 2 points)
d (distance between 2 points)
Lenz’s law definition
any induced current or induced emf will be established in a direction so as to produce effect which oppose the change that is producing it
Right hand rule generator edition
Thumb: force applied to cause motion
Index: magnetic field
Middle: current inside conductor
Used when force makes current
Lenz’s law conservation of energy and key formula
W = F x
W = P ∆t
ε = B L v N
ε is emf across conductor
Magnetic flux linkage
ψ = B A cosθ N
ψ flux linkage
B magnetic field density
A area linked to magnetic field
N number of loops
Faraday’s law definition
magnitude of induced emf is proportional to rate of change of magnetic flux linkage
Faraday’s law emf formulas
ε = - [ ∆ψ / ∆t ] N
Generating AC currents
flux
ψ = BA cos(ωt)
emf
εₜ = ε₀ sin(ωt)
pd (with closed circuit)
Vₜ = V₀ sin(ωt)
current
Iₜ = I₀ sin(ωt)
(V = RI and θ = ωt)
Use cos if variable starts at max when crossing origin and use sin if variable starts at zero when crossing origin
AC- Power formulas
peak power:
P₀ = V₀² / R
or
P₀ = I₀² x R
mean power:
Pₐᵥ = 0.5 x V₀² / R = V²ᵣₘₛ / R
or
Pₐᵥ= Iᵣₘₛ² x R = 0.5 x I₀² x R
root mean square:
Vᵣₘₛ = V₀/√2
Iᵣₘₛ = I₀/√2
Transformers
Vs/Vp
Ns/Np
=
Ip/Is
Flux
Amount of magnetism, unit: Wb
Flux density
How tightly packed together are the field lines
B, unit: T (tesla)
Direction of current into or out of plane
Dart method
Dot: into plane
Cross: out of plane
Additional flux formula
B = mg/IL
Emf and flux graphs against t - for coil entering and exiting uniform magnetic field
phi / t
zero grad at zero
constant positive grad
zero grad at constant
constant negative grad
zero grad at zero
- emf / t
zero grad at zero
vertical upwards
zero grad at constant
vertical back to zero
zero grad at zero
vertical downwards
zero grad an negative constant
vertical back to zero
zero grad at zero
Stationary coils
In order to induce emf, flux density over time must be changing as area of coil remains constant
Flux linkage
Same as flux but with multiple turns hence formula is
Flux linkage = BAN