unit 4 - magnetism Flashcards
Magnetic Field lines defination
Imaginary path in which the magnetic north monopole travels in the presence of an External Magnetic Field
Properties of Magnetic Field Line
1) The direction of MFLs indicate the direction of the MF field at that point
2) The density of MFLs in an indicator of the magnetic field strength in that area
3) MFLs form close loops
4) MFLs appear to emerge from the North Pole and Appear to terminate at the south pole
5) No 2 field lines every intersect each other
Why cant 2 MFLs intersect
Because the magnetic north monopole will then have 2 directions to travel which isnt possible
Conventions of Magnetic Field - Going into the page
North pole and represented with Circles (remember using GON)
Conventions of Magnetic Field - Coming out of the page
South pole and represented with X
How to determine direction of magnetic field in straight current carrying wire
Using Right hand grip rule, Imagine holding the wire in ur right hand such that the thumb represents the direction of conventional current, then the 4 fingers represent the direction of magnetic field.
How to determine the direction of magnetic field in solenoid/loop
Using right hand grip rule modified
Out stretch the 4 fingers of your hand to represent the direction of conventional current and then the direction of the magnetic field is represented with ur thumb
Factors affecting MF strength generated by a Solenoid
1) No. of coils
2) Current and PD
3) No. of coils per unit length
4) Material of the core
5) Distance of point of measurement of MF from solenoid
how to find Magnitude and Direction of force acting on a straight current carrying wire
Magnitude = F = BIL
B = strength of external magentic field in tesla
Direction = Right hand Palm rule/ Flemming’s Left hand ruke
right hand palm rule
Outstretch the 4 fingers of you right hand to rep the direction of MF and the thumb to rep the direction of conventional current. Then the direction of palm indicates the direction of Magnetic Force
Magnitude and Direction for force acting on a moving charge
Magnitude: F = B * q * v
v = speed of moving body
q = charge on moving body
B = strength of external magnetic field
Direction: Right hand palm rule or Flemings left hand rule
1 amp current
If the force per unit length between 2 parallel current carrying wires carrying the same amount of current separated by 1 mtr distance in air or vacuum is 2 * 10^-7 Nm-1, then the current flowing through each wire is said to be 1mp
Magnetic Flux defination
Measure of the no. of field lines passing parallel to perpendicular to the area of cross section
Formula for magnetic flux
ɸ = BAcosθ
B = Mf strength
A = area of cross section of loop
θ = Angle formed between direction of MF and perpendicular to the area of cross section
Magnetic Flux linkage
Magnetic flux lineage associated with ‘N’ number of coils
Formula for magnetic flux linkage
ɸ = NBAcosθ
Faraday’s law of electromagnetic induction definition
The induced potential difference/EMF is directly proportional to the negative rate of change in magnetic flux linkage
what should be done to constantly produce voltage through Magnetic flux linkeage
Magnetic Flux linkage must be constantly changing over a short period of time to sustainably produce voltage. The shorter the time, the greater the voltage produced.
Factors affecting the induced Electromotive Force?
1) No. of coils
2) Strength of external magnetic field
3) Area of cross section of loop
4) Angle formed between the direction of MF and the perpendicular to the area of cross section
Faraday’s 3 experiments what were the reasons and conclusions?
1) Bar magnet in relative motion with a Solenoid (to see if induced current can be produced w/ bar magnet). Conclusion was that relatvie motion changes the MF and creates induced EMF
2) To see if a bar magnet is required or will an electromagnet work? It was done to see if a bar magnet is required or will an electromagnetic also work. The answer was any object that creates a magnetic field will work
3) to see if relative motion is required to generate electricity. Rationale was to find other factors affecting Flux Linkaeg to sustain EMF creation. The observation was that realtvie motion isnt requires, changing either the feild strenght, number of coils or the angle theta would work
How can we sustain the infuced EMF created by Flux linkage
Magentic flux linkage must change over a very short period of time and must contstantly keep changing. If the change happens in a shorter period of time, then the voltage produced will be higher
Electromagnet
Device which exhibits a MF when current flows through it
How to create EMF/voltage using magnetic flux linkage in real life in power plants?
By changing the angle formed the direction of magnetic field and the perpendicular to the area of cross section
Alternating Current
Flow of current changes periodically, the +ve and -ve terminals change
Which is more common AC or DC? and why
AC as it is easier to transport from one place to another. It can be easily stepped up and down in voltage using transformers, which allows for efficient transmission over long distances by minimizing power loss. Many factories already produce AC and hence there isnt a need for an extra conversion step
Direct Current
No change in flow of current
Transformer
A device which minimises the power lost and is a device used to transmit electricity from the power generating station to the end user
What happens in the primary of a Transformer
AC is inputted and that changes the flux linkage and this is transferred onto the secondary by the Laminated core
What happens in the laminated core of a transform
Multiple plates are put together to restrict the flow of electrons and minimise power loss. Generally made of a soft iron core and transfers the chnage in flux from the primary to the secondary
Ideal transformer
No energy and flux lost as flux in primary and secondary remains the same
Formula for ideal transformer
Vp/Vs = Is/Ip = Np/Ns
Step Up transformer
Used at the Power generating station
It is where the voltage at secondary is greater than voltage at primary. To achieve this, the number of coils at the primary is less than the number of coils at the secondary.
The current in primary is greater than the current at secondary
This si done to minimise power loss. As electrical energy is transported at high voltage to minise power, to acheiev this high voltage, we must use Step up transformers
Step down transformer
Used at the End user
It is where the voltage at the primary is greater than the voltage at the secondary by making the number of coils in the primary more than the number of coils at the secondary
The current as secondary is greater than the current in primary
Appartus used to measure Magentic field strength
Vernier Magnetic Field sensor to capture the data and LabQuest to display the readings
When is Magnetic flux linkeage maximum and 0
It is 0 when the perpendicular to the area of cross section is perpendicular to the field line, ie when cos = 0
It is max when perpendicular to the area of cross section is parallel to the magnetic feild lines, ie when cos = 1
Electromotive Force
Voltage/Potential Differene
How do turbines generate EMF
The coil in the turbine rotates in the prescnce of an external Magnetific Feidl. This rotation causes a change in the value of theta which chanegs the value of flux linkage. The turbine rotates very fast and hence flux linkage is changed very often, producing sustainable AC current
