SAC 3 - created from Mind Map_1

Page 1

Magnets

Motors

Transformers

Power transmission

Filled with Dipoles

Soft or hard

Cannot seperate a N and S pole

Magnetic field

Flux

Dipoles randomly arranged

Dipoles arranged in one line

No magnetic effect

Magnetic effect

Soft easy to de/magnetise

Hard hard to de/magnetise

Region where a magnetic material experiences a force

Forces Diagram

https://upload.wikimedia.org/wikipedia/commons/thumb/0/0c/VFPt_cylindrical_magnet_thumb.svg/250px-VFPt_cylindrical_magnet_thumb.svg.png

Field lines travel from N to S

Earth's Magnetic Field

http://www.epa.gov/esd/cmb/GeophysicsWebsite/pages/reference/_img/NewImages/Magnetic%20Susceptability/earth-magfield.jpg

What we call the North Pole is actually the earth's South Pole. Due to this north magnets are attracted to it.

Vector

Magnetic fields are always apparent when current flows

Field is stronger closer

On diagrams..

x goes into the page

. goes out of the page

Think of a feathered arrow. Cross at the back going away from you.

Field Strength (B)

Force on an electron in a field

F= BvQ, where v = velocity and Q = charge (charge = 1.6E^-19 for electrons)

E.g. compass

Force Formula

F=nBIL

Where N = Number of wires, B = Field strength (Tesla), I = Current (amperes) and L = Length of wire in field (m)

This works when perpendicular when not, F=nBILsin(theta). Where theta is the angle between current and field.

If Current and Field is parallel, F=0

Field Diagram and Right Hand Grip Rule

http://courses.ae.utexas.edu/ase463q/design_pages/fall02/wavelet/3_sour8.gif

Parallel Wires

http://www.physchem.co.za/OB11-ele/graphics/magnetic1_f8.gif

Right Hand Solenoid Rule

http://etc.usf.edu/clipart/35600/35671/rhrsole_35671_md.gif

Solenoid Field Diagram

http://www.met.reading.ac.uk/pplato2/h-flap/phys4_4f_4.png

When current flows field strength equals

B = (kI)/r

Where k is a constant, I is current and r is radius.

If current and field are parallel, F=0

Right Hand Slap Rule

http://www.ph.unimelb.edu.au/~mkl/640162/prot/module1/image/RHruleI.gif

Tesla (T)

Typically...

Permanent magnets typically are B = 10^-3 to 1T

The Earth's field is B ~ 5x10^-5T

The amount of magnetic field in a region

Wb = B x A

Where B = Field strength (T) and A = area (m^2)

Amount of turns is irrelevant

If field and coil parallel, = 0

EMF

Moving a conductor parallel to a field line changes nothing

To find Change in F rate, use quarter rotation, not full

No change in flux when completely in field

Size and density

Area not diameter!

Convert dimensions to m before calculating area

Voltage

Created by batteries, generators etc.

Formula

-nA*(Change in B/Change in time) OR -nB*(Change in A/Change in time) FOR AVERAGE OVER TIME -n*(Change in flux/Change in time)

N = Turns

Currents are not always induced

Fleming's RH rule

http://www.diracdelta.co.uk/science/source/f/l/flemings%20right%20hand%20rule/image001.jpg

Lenz's Law

As a magnet passes through a coil, a current is induced due to the presence of a magnetic field. This causes the coil to oppose this magnetic change by switching the direction of the current.

For coils...

Can also be used for coils; do one side, then use direction to show current

DC

http://electrical4u.com/electrical/wp-content/uploads/2013/03/dc-motor-parts.jpg

Generators

RHS can be applied

Motor requires split ring commutator

http://fcw2.needham.k12.ma.us/~michael_h/Physics/FOV1-00112C20/FOV1-00112C2C/S045D68FC.0/1713_105349_0.png

To increase turning force increase n, B, I or L or use a wider motor.

Results in Torque

Commutator repeatedly changes direction of current and force

DC (Dynamo)

"DC Motor in reverse"

You spin, it produces voltage/current

Max V when parallel to the field, Min when perpendicular

RMS

Only work on AC

Changes number of turns on input compared to output

Power in = Power out for "ideal transformer"

E.g. If Voltage increases, current decreases (As P=VI)

Done in Ratios

N1/N2 = V1/V2 = I2/I1 Where N = Turns

AC RMS is equivalent of DC not RMS; should be equal

Doesn't work on cells, batteries, etc.

DC can't have EMF induced as flux can' be time-varying

Amplifies/diminishes voltage by inducing EMF in the secondary coil

Increase V to decrease I

Heat is the mechanism by which we lose Power

Voltage Drop experienced across cables

As power usage increases, so does current flow

P=VI

Less I, the more efficient

Power Loss Formula

P=I^2R

V=IR (IR OF CABLES)

Delivered voltage falls