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5.1
Circuit rules
Current rules:
1. At a junction, the sum of the currents leaving equals the sum of the currents joining.
0.3 A
0.7 A
( this is because the charge entering each second
equals the charge leaving each second and there
is no build up of charge at the junction.)
? A
0.2 A
0.2 A
0.2 A
2. Components in series:
A
0.2 A
a) current entering a component = current leaving
b) current passing through components in series is the same through each component
5.1
Circuit rules
Rules for potential differences
5.1
Circuit rules
battery pd = 12V
This means:
If the variable resistor
is adjusted so that there
is a pd of 4V across it
This means:
each coulomb of charge
uses 4J of energy
passing through it
each coulomb of charge
leaves the battery
with 12J of electrical
energy
5.1
Circuit rules
3. For any complete loop of a circuit, the sum of the emfs equal the sum of potential drops
round the loop.
This follows from the law of conservation of energy:
The total energy per coulomb produced = the total energy per coulomb delivered
5.1
Circuit rules