Module 4 Chapter 3 Electricity: Electrical Circuits Flashcards
What is Kirchhoff’s first law?
The sum of the currents entering a junction is equal to the sum of the currents exiting the junction.
Kirchhoff’s first law is a consequence of…
the conservation of charge.
What is Kirchhoff’s second law?
In any closed electrical loop, the sum of the potential differences across each component is equal to the e.m.f
Σℰ = ΣIR
What do you do when there are two sources of e.m.f (ℰ)?
You add the two sources together to form one source, remembering that the direction of the flow of current from each of them matters; if they flow in opposite directions, they will cancel each other out so you subtract the smaller ℰ from the larger ℰ.
What is a series circuit?
A circuit with all components in a single electrical ‘loop’.
What can be said of the current in a series circuit?
It is the same at every point in the circuit.
What can be said about the potential differences across the components in a series circuit?
Their sum is equal to the e.m.f (ℰ).
What can be said about the resistances of each component in a series circuit?
their sum is equal to the circuit’s total resistance.
What is Ohm’s law?
V = I * R
potential difference = current * resistance
How do you find the total resistance for a series circuit?
R = R1 + R2 + R3…
How do you place an ammeter in a circuit?
In series with the loop across which you want to measure the current.
How do you place a voltmeter in a circuit?
In parallel across the component or components whose potential difference you want to measure.
What is a parallel circuit?
A circuit with components in two or more electrical ‘loops’.
How do you find the total resistance of a parallel circuit?
1/R = 1/R1 + 1/R2 + 1/R3…
with each of the numbered Rs being the resistance of an entire ‘loop’ which can be found by adding the resistances of each component on that branch.
How is current shared between branches of a parallel circuit?
It is divided between them (see Kirchhoff’s first law) branches with a higher resistance get less current relative to those with lower resistance.
