C10 - Kirchoff's Laws and Circuits Flashcards
What is Kirchoff’s first law?
For any point in an electrical circuit, the sum of currents into that point is equal to the sum of currents out of that point.
What is Kirchoff’s second law?
In any circuit, the sum of the electromotive forces is equal to the sum of the voltages around a closed loop.
What is a series circuit?
One which has only one path for the current, a single loop from one terminal of the source of e.m.f. (e.g. a cell) back to the other terminal.
Current is the same in every position.
E.m.f. Is shared between components.
What’s a parallel circuit?
One which provides more than one possible path for the charges.
How much charge flows down a path depends on the resistance of each path.
How is total resistance calculated in a series circuit?
R = R1 + R2 + R3…
Sum of all resistors.
How is total resistance calculated in a parallel circuit?
1/R = 1/R1 + 1/R2 + 1/R3…
Therefore 1/R is inverted to calculate the value of R.
What are lost volts?
When current flows through the cell a voltage develops across the internal resistance.
This voltage is not available to the circuit so it is called the lost volts
What is internal resistance?
Resistance within a battery or cell.
What’s the relationship between emf and lost volts?
E.m.f = terminal p.d. + lost volts
e = V + Ir
How are lost volts calculated?
V = Ir
Lost volts = current * internal resistance
What is a potential divider?
An electrical circuit designed to divide the potential difference across two or more components (often two resistors) in order to produce a specific output.
The p.d. across each resistor depends on the ratio of their resistances
What is a potentiometer?
A variable resistor with 3 terminals and a sliding contact.
When the contact moves towards A, V out increases until at A it is equal to V in.
When moved towards B, V out decreases until at B it is 0.
How is emf calculated?
e = V + Ir
Or
e = IR + Ir
What’s electron drift velocity?
The net average velocity of electrons traveling through a metal
What’s electron drift?
When electrons move in one direction when connected to a power source
