# Physics Electricity And Magnetism

version from 2018-01-27 03:26

## Electricity and circuits

Matter with opposite chargesAtracts each other
Matter with like chargesRepels other
Charged matter with neutral objectAttracts
How do objects obtain electric charge?contact, induction, friction
GroundingDischarging an object via a connection to earth
Coulomb6.25*x10^18
Electron charge1.6*10^-19 (Coulomb)
Overall charge on an object formula (Q)Q = N*(1.6*10^-19)
Current formulaCharge/Time => I = Q/t; 1Q/t = 1A
DIrection of electronsElectrons travel from the negative terminal to the positive terminal
VoltsEnergy (Joules) for every charge; V = E/Q
Energy in circuitE = V*I*t (combine volt equation and current equation)
OHM's LawR = V/I
Kirchoff's voltage lawThe total voltage is equal to the sum of all voltages along a path
Kirchoff's current lawThe sum of the parallel circuit amps must equal the total amps
Resistance in series(Rt) = (R1) + (R2) + ...
Resistance in Parallel1/(Rt) = 1/(R1) + 1/(R2)

## Magnetics

Law of magnetic forcesSimilar magnetic poles repel; Unlike poles attract
What type of metals to magnets attract?Ferromagnetic metals
What are examples of ferromagnetic metals?- Iron
- Nickel
- Cobalt
Domain theory of magnetsAll magnets are made up of many smaller magnets called DIPOLES. If Dipoles align a small magnetic domain is produced
Oerstad's principleCharge moving through a conductor produces a circular magnetic field around the conductor
Left hand rule #1Grab conductor with left hand and have thumb pointing in direction of current flow.
The curved fingers show the direction of the magnetic field
Left hand rule #2(Used for solenoids) Grab coil with left hand and curl fingers to represent current flow.
Direction of thumb is the "north" end of the magnetic field
Left hand rule #3(Usually used for the motor rule) Using the a straight left hand, point the fingers in the direction of the external magnetic force and point the thumb in the direction of current.
Where palm faces is the direction the force
SolenoidWhen a large number of loops are wound close together to form a coil
Factors that affect magnetic field strength- More current
- more loops
- core has ferromagnetic material
- loops on coil are smaller

## Motors

CommutatorPrecicely cut ring which allows for current to be switched in mid-rotation
Brushes"sticks" which complete the circuit
ArmatureThe actual magnet
What does motor speed depend on?- Current
- type of core
- number of coils
- strength of external magnets
- spacing of coils
How is the motor made more powerful and efficient?Increase number of windings, use stronger magnets
Speed of rotation is controlled by...Voltate
How motor worksThe armature is attached to a commutator which in turn is touching the brushes.
When a current is present, the armature (solenoid) gains a magnetic field and either attracts or repels the magnet according to the magnets which surround it.
When the armature reaches a certain rotation, the current direction is switched and the armature continues to move