Magnetic Feilds And Induction Flashcards
What are magnetic feilds
Are induce with the movment of charges
Why are electrons induced by a magnetic feild
Electrons make up the atomic structure are in motion around a nucleus
What metals are ferromagnetix
Iron
Nickel
Cobalt
What does ferromagnetism mean
It is when the magnetic dipole can be made to align resulting in the material becoming magnetised
What is the hand rule for a magnetic field with a straight wire
Left-hand (like doing a thumbs up)
Thumb - electron
Fingers - feild lines
How can a magnetic field be strengthen
By coiling up the wire
Whaf is a long coil
Solenoid
What is the rule for solenoids
Left hand - curl around a water bottle
Finger indicates electrons
The points north of the magnetic field
What is a solenoid
It is a coil of wire thaf when a current flow through it a uniform magnetic field is produced inside the volume of space of the cylinder
What is the rule for finding the force on the conductors
Right hand rule
Middle finger- electron
Top finger - magnetic field
Thumb - force
What happens to a conductor moving in a magnetic feild
It will experience a force which is a result of the magnetic induction
What is the unit for magnetic induction
Tesla
For a strong nuclear force what is:
The relative magnitude
Range
Example
1
X10-14
Nucleons in a nucleus
For electromagnetic force what is:
The relative magnitude
Range
Example
x10-2
Infinity
Contact forces
For a weak nuclear force
The relative magnitude
Range
Example
x10-5
x10-18
Beta decay in the nucleus
Foe the gravitational force what is:
The relative magnitude
Range
Example
x10-38
Infinity
Very large masses
Planets
What is the component velocity for perpendicular
Vsin0
What Is the component velocity for parallel
Vcos0
What type of motion will a charged particles with a perpendicular velocity face
It will undergo circular motion
If the magnetic feild acts into the page then the following applies
Positive- anticlockwise
Negative- clockwise
What are the applications of magnetic feild
Velocity selector
Mass spectrometer
What is the arrangement for a velocity selector
If the magnetic and electric field are perpendicular to eachother. A charge with a certain velocity will proceed through the crossed fields undefeated
Only if forces are balanced
If order to calculate the velocity in the velocity selector what do you do
You equal f=qvB and f=qE
Then make it equal to velocity
What is a spectrometer used for
It is used to measure the range ot atomic masses of ions of an element.
Whaf happens during the mass spectrometer
They go through the velocity selector
They then enter a magnetic field which causes then to follow a circular path
How to calculate the radius in the mass spectrometer
qvB=mv^2/r
Symbol for magnetic induction
B
Symbol for a battery
One big line one small
Symbol for a capacitor
Two big lines
What is the time constant
Time taken to increase the charge stored by 63% of the difference between initial charge and full charge
What percentage is the time constant
63%
What is the time constant for discharging
37%
What is the discharging time constant definition
Time taken for a capacitor 5o discharge to 37% of it’d initial charge
What are conductors
They contain free electrons that are not strongly boned to any particular atom.
What happens when an emf is applied to a conductor
The electrons dirft along the conductor. This movement of charge is knows as current
What angle are the charged particles at to the magnetic feild
Right angles
If magnetic feild lines are bring crossed what is produced
EMF
Another way can a induced EMF be produced
Stationary conductor
What does the induced voltage depend on
Size of coil, strength of magnetic, rate of change of motion of the magnetic
When the rate of chnage of current is zero
Max current is reached
What is the back emf a result of
A decrease in the rate of change of current which in turn decreases the back emf.
Symbol for inductance
L
What is the symbol for back emf
Curly E
Unit for rate of change of current
As-1
Units for inductance
H
Why is the minus sign present on back emf
Because back emf is in the opposite direction to the forward current
How happens to the back emf when the rate of change of current decrease
It will decrease
What does the power supply of the circuit
It was to work against this back emf. This work is stored in the magnetic field around the inductor
Whaf happens to the engery stored when the magnetic field collapses
The engery is immediately released
Whay does the core of a inducer allow for
Storage of energy and controlling of the time it take to get to maximum current
Symbol for an inductor (in q circuit)
The swiggle line
Does the current reach maximum when their is a induction in the circuit
No
What is the back emf equal to
Equal but opposite to the supply supply
What does a graph of current against time look like
Increase gradient curve from 0
Self - inductance
When a circuit it switched on a sudden change in current produces a changing magnetic feild around the coil that induces emf across the coil
What is lenz’s law
States that the induced current (and emf) is always in such direction as to opposed the change that is causing it
Back EMF
Is an induced EMF in a circuit as a result of a changing magnetic feild that opposes the current in the circuit
If you increase the a.c supplies frequencies then what happens to the rate of change of current
It increases
If the rate of change increases then what happens to the back emf and current
The back emf will also increases
If the rate of change increases then what happens to the self induced back emf and current
The back emf will increase and opposed the chnage so the current will decrease
Inductive reactants is a property that…
Arises for inductor in ac circuits as they are frequency dependent components
Symbol for inductive reactance
XL
Inductive reactance is the opposition to
Changing current
If the frequency of the ac supply is high then what happens to the chnage jn current
Large
Ac circuits must deal with what
Resistance qnd reactance
Graph of inductive reactance in a inductor against frequency
Straight line
Inductive reactance in a capacitor against frequency
Sloping down decreasing gradient
What reactance and frequency does capacitors have
Low reactance and high frequencies
Inductor reactance and frequencies
Low reactance
Low frequency
What is the diode for
Reverse bias to the power supply. This prevents it from contributing to the circuit during charging
Explain why high frequency signals pass to the component with the capacitor
Capacitor has how reactnace for higher frequencies
Explain why low frequency signals were passed through the inductor
Inductor have low reactance at low frequencies
It was advised to include q diode in the circuit to prevent damage to the laptop when the switch is open. Why is this necessary
Large back emf
Explain how the back EMF is produced
Their is a chnage in current which produces a chnage in magnetic field
By considering the magnetic feild around the inductor, explain why the back EMF produced is large enough to allow the neon lamp to flash
The magnetic feild collapses around the inductor and causes a rapid chnage in current
The inductance of an inductor increases state and happens to the frequency and justify
Frequency decreases
Increases inductance increases the time constant
Definition of inductive reactance
Is the opposition to changing current
What is inductance
It isbthe ratio of the induced back emf to the rate of change of current
When the battery I’d switched on what is thr back emf
Equal to the supply voltage
At Imax whaf is the back emf equal to
0V
Capacitive reactance
The opposition a capacitor to changing current
