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