Magnetic Fields Flashcards
Motor effect
Current makes force
Dynamo effect
Force makes current
Dynamo effect and motor effect link
Dynano effect tried to stop motor effect
Apply force
1.creates current
2. motor effect
3. This current creates force in opposite direction
Lenz Law
The direction of an induced current is such that it would oppose the change that caused it
If the top of the solenoid is North Pole what direction does current rotate
Anticlockwise ( N )
Mass spectroscopy purpose
Finding the mass of a particle
What’s the similarities/ difference of Grwvitation and electrostatic forces
Similar = inverse square law
-use of field lines, use of potential, equipotential surfsced
Mass always attracts, charges may attract or repel
Mass spectroscopy
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Cyclotrons
- to increase radius, polarity of electric field switches, accelerating the proton
r = mv / (BQ)
F = BQ/2pim T = 2pir/v
F = frequency of the alternating voltage
Q = charge of the particle (C),
B = magnetic field strength (T),
M = mass of the particle (kg).
When flux increases from 0 to 2 linearly,what happens to emf …and back from 2 0
EMF instantly increases to a value = gradient and stays there as flux increases linearly so emf remains constant..
when it’s fully entered the coil, the flux stays the same so emf induced = 0
- when exiting, the flux reduces from 2 to 0 linearly, so the gradient is negative and emf induced is a maximum but in opposite direction and then when the conductor has left the coil emf instantly goes to zero.
Back EMF
When motor spins, produces dynamo effect due to lenz law
-supply same V to motor
-opposing emf is high when spinning fast
-unloaded
-opposing emf is small
-heavy load
EMF induced entering a coil
-Eo = BANw
E = Eocos(wt)
E = BANwcos(wt)
Half wave rectification
-so a normal sin wave but the negative y values are removed so there’s a gap inbetween
Full wave rectification
Modulus of a sin graph
Power for AC
Vrms x Irms
What is permitivity
Permittivity is the measure of how easy it is to generate an electric field in a certain material
If the polar molecules align and their opposing electric field increases what happens to permitivity
Increases
Why do polar molecules increase capacitance
-oppose electric field produced by the plates
-reduces overall electric field
-decrease potential between the plates
-Capacitance increases
What happens during charging
-power supply pushes electrons from positive to negative plate
-does work on the electrons so electrical energy becomes stored on the plates
-as more charge builds up on negative plate. Repulsion increases
-more work needed to push electron so voltage increases
What does time constant mean for a charging capacitor
The time taken for the charge or voltage of a charging capacitor to rise to 63% of its maximum value
What does time constant mean for a discharging capacitor
The time taken for the charge, current or voltage of a discharging capacitor to decrease to 37% of its original value
Why does a conductor cutting field lines Create an EMF
-The upwards motion of the wire as it cuts across the magnetic field lines gives rise to an emf within a wire
E = BLV
How can you explain Lenz law when cutting field lines
- so when the electron moves to one side and the other side of the conductor becomes positive. An emf is created
-However current would flow from the electron to positive side which creates a force downwards.. this means you have to do work to move the wire upwards to oppose the downwards force
