Topic 2: Electricity

Equation for Electric Charge

Electric charge= Current x Time

Q=IxT

Unit of Electric charge (Q)

Coulombs (C)

Unit of current (I)

Amps (A)

Unit of Time (T)

Seconds (S)

Resistance

How difficult it is for current to flow

Equation for Power

Power= energy/time

Unit of Power

Watts (W)

Unit of energy

Joules (J)

Equation for Potential Difference

Potential difference= Energy/Charge

Unit of potential difference

Volts (V)

Ohms Law

Potential difference= Current x Resistance

Ohms Law rules

V=IR

V is directly proportional to IR

I is inversely proportional to R (and vice versa)

Resistance

Measured in Ohms

Equation for Power

Power= Current x Potential Difference

P=IV

V=IR

P=I²R

Resistors in series

R1+R2+R3+etc.

Resistors in Parallel

Less than the smallest value

Ohmic resistor

Has a constant resistance

Live wire

Brown

Brings current to the applicance

Neutral Wire

Blue

Takes current away from the appliance

Earth wire

Green/Yellow stripes

Takes away excess current

Fuse

Built into the live wire, melts if the current is too high and breaks the circuit

Thermistor

As temperature increases, resistance decreases

LDR

Light Dependent Resistor

A.C.

Alternating current, constantly changing direction

Mains supply

230V, 50Hz

D.C.

Direct current, batteries

Step up transformer

Increases Potential Difference

Step down transformer

Decreases Potential Difference

Static electricity

When an object is charged through friction, negatively charged electrons move from one surface to another, leaving one side with less electrons so it has a positive charge and the other with a negative charge.

Force field

A region of space in which force can be exerted

Electric field

Region of space in which an electrically charged particle will feel a force

Sparks

Occur when an electric field is very strong.

It causes an insulator to break apart and form positive and negative ions. Charger particles experience a force due to the electric field and move- producing the spark

Double insulation

No earth wire, whole appliance covered in plastic

Transformer equation

Vp/Vs = np/Ns

VP= voltage, primary coil

Vs= voltage, secondary coil

np= number of turns, primary

ns= number of turns, secondary