4.3 Electrical Circuits Flashcards
What does Kirchhoff’s Second Law state?
Kirchhoff’s Second Law states that:
In any circuit, the sum of the electromotive forces is equal to the sum of the potential differences around a closed loop
Σϵ = Σv around a closed loop
Which conservation principle is the basis for Kirchhoff’s Second Law?
Kirchhoff’s Second Law takes the law of conservation of energy and applies it to electrical circuits. It essentially says that the total energy transferred to the charges ( Σϵ ) in a circuit is equal to the total energy transferred from the charges ( Σv ) as they move around the circuit.
Describe the current in a series circuit
In a series circuit, the current is the same in every poisiton
This is because we know from Kirchhoff’s First Law that the rate of flow of charge is the same is the same at all points in the circuit, as there is only one single loop for current to flow through, and the charge is not being used up, it is just flowing through the circuit.
Kirchhoff’s First Law: For any point in an electrical circuit, the sum of currents into that point is equal to the sum of the currents out of that point
Describe the relationship between the e.m.f, and the p.d. of components across a series circuit.
Since a series circuit has only one closed loop, then from Kirchhoff’s Second Law, the e.m.f is shared between the components.
The sum of the p.d.s across the components is equal to the e.m.f
What does the p.d. of each component in a (series/parallel) circuit depend on?
The p.d of each component in a (series/parallel) circuit depends on the resistance.
→ If the circuit contains two components with the same resistance, then the e.m.f is shared equally between them
→ If the circuit contains components with different resistances, then the component with the greater resistance will take a greater proportion of the e.m.f.
This is due to the formula V = IR
Describe how we calculate the p.d.s of components across a series circuit when there is more than one e.m.f
In a series circuit with more than one e.m.f, you have to add or subtract the e.m.f.s depending on the polarity of the sources before sharing it between the components
Describe the current in a parallel circuit
A parallel circuit provides more than one possible path for the current / flow of charge. However, the total charge remains the same because of Kirchhoff’s 1st law.
The charge down each path depends on the resistance of the path - as V=IR.
The greater the resistance of the branch, the lower the current that passes through it.
Remember, current chooses the path of least resistance.
Describe the relationship between the resistance of a branch in a parallel circuit, and the current
The greater the resistance of the branch, the lower the current that passes through it. This is because V=IR
- Using this formula tells us, that if one branch has half the resistance of the other, it will have twice the current through it.
Remember, current chooses the path of least resistance.
