Cheatography

# Generation and Transmission of electricity Cheat Sheet by cadmiumium

VCE unit 3 electricity

### magnetic flux

 Φ=B⊥A
·B=mag­netic field strength (T)
·A=area perpen­dicular to the magnetic field (m²)
·Φ=mag­netic flux (Wb)

 ε=-N(∆­Φ/∆t) ε=EMF(V), N=number of turns in coil
·(∆Φ/∆t) is the derivative of Φ with respect to time.
·ε graph should be negative when Φ-t graph has +ve gradient
·ε graph should be positive when Φ-t graph has -ve gradient

### Lenz's Law

 An induced current will flow in a direction such that the magnetic field created by the current will oppose the change in flux that induced the current.
Right Hand coil rule:
·thumb: direction of induced magnetic field
·fingers: direction of induced current

### generators and altern­ators

 f=1/T f=freq­uency (Hz), T=period of revolu­tion(s) - time taken to complete a full cycle *max ε when coil is parallel to magnetic field, ie. greatest rate of change *DC current can only be produced in presence of a split ring commutator Alternator (AC): sinusoidal DC generator: modulus of AC
·Φ(t)=­aco­s(2πft)
·ε=Φ'(­t)=­-2a­πfs­in(­2πft)

### electr­icity recap

 V=I·R - V(V), I(A), R(Ω) P``supply``=V·I - also: power rating P``dissipated``=I²·R=V²/R Power (W) is the rate of change of energy with respect to time P=∆E/∆t - gradient of E-t graph
series circuit:
·current (I) is the same through the whole circuit
·flow: from positive to negative terminal
·total resistance (RT) is the sum of individual resist­ances: R
``1``
+R
``2``
+…
·total voltage supplied to a circuit must be equal to the total voltage used around the circuit (sum of voltage drops): V
``supply``
=V
``1``
+V
``2``
+…

### Transf­ormers, comparing AC and DC

 V``RMS``=V``peak``/√2 , I``RMS``=I``peak``/√2 P``avg``= V``RMS``⋅I``RMS`` = I``RMS``²⋅R = V``RMS``²/R - avg power delivered by sinusoidal signal Transf­ormers: P``in``=P``out`` VI``primary``=VI``secondary`` V``1``/V``2``=N``1``/N``2`` I``1``/I``2``=N``2``/N``1`` when V``1``>V``2``: Step-down transf­ormer when V``1``

### Transm­ission of power (Power systems)

 Power loss: P``loss``=I``line``²·R``line`` Voltage drop: V``drop``=I``line``·R``line`` I``load``/I``line``=N``1``/N``2``
·almost all wires have some resistance
·as electr­icity passes through the wires, it causes them to heat up, resulting in power loss, and a decrease in the voltage that is available at the load.

### High voltage transm­ission

·we can reduce power loss by lowering the current in the line
·we can keep the same supply power by increasing the supply voltage
·this is done using transf­ormers.