Module 4 - Section 1 - Conservation Of Charge And Energy In Circuits

Question 1

What is the conservation of charge ?

Answer 1

The conservation of charge means that as charge flows through a circuit - it doesn’t get used up or lost

This means that whatever charge flows into a junction will flow out again

Kirchhoff’s first law states that the total current that enter a junction is equal to the total current leaving the junction

Question 2

What is Kirchhoff’s second law and what physical quantity is conserved ?

Answer 2

The total emf around a series circuit = the sum of the pds across each component

The physical quantity conserved is charge

Question 3

What’s the difference between emf and pd ?

Answer 3

EMF is the energy transferred to a unit charge
Pd is the energy transferred from a unit charge

Question 4

What are the rules for a series circuit ?

Answer 4

• The current is the SAME at all point of the circuit - as there are no junctions - nowhere for the current to split
• e.m.f is split between the components - Kirchhoff’s second law - so emf = v1 + v2 + v3 …
• The total resistance of a series circuit is just all the resistance of the components added up - Rtotal = R1 + R2 + R3 ….

Question 5

What are the rules for a parallel circuit ?

Answer 5

• the current is split between branches - so i = i1 + i2 + i3
• Same pd across all components
• resistance in a parallel circuit = 1/Rtotal = 1/R1 + 1/R2 + 1/R3