Module 4.3 - Electricity: Electrical Circuits Flashcards
What is Kirchhoff’s first law?
The sum of currents ENTERING a junction in a circuit is EQUAL to the sum of currents LEAVING the junction - a form of conservation of charge.
What is Kirchhoff’s second law?
The sum of e.m.f. is EQUAL to the sum of the P.D. in a closed loop - a form of conservation of energy.
∑e.m.f = ∑IR
Describe Series circuits
> Current SAME at all points
e.m.f. is equal to the sum of p.d. across the resistors
Total resistance is equal to the sum of individual resistors
How do you work out the total p.d. in a series circuit?
Vt = V1 + V2 + V3 + …
How do you work out the total resistance in a series circuit?
Rt = R1 + R2 + R3 + …
Describe Parallel circuits
> Total current is the sum of the individuals branch currents
The potential difference across the resistors in each branch is the same and equal to the e.m.f.
How do you work out the total current in parallel circuits?
It = I1 + I2 + I3 + …
How do you work out the e.m.f. of parallel circuits?
e.m.f = V1 = V2 = V3 = …
How do you work out the total resistance of parallel circuit?
1/Rt = 1/R1 + 1/R2 + 1/R3 + …
How do you find the output voltage, Vout, of the resistor, R2?
Vout = Vin x ( R1 / R1 + R2)
When is the output voltage of R2 the largest?
When Vin and R2 are large, and also when R1 is smaller than R2
Define Internal Resistance, r
The resistance of a SOURCE of e.m.f
Why is some energy lost when charge carriers flow through a source of e.m.f?
Internal resistance causes the charge carriers to do work against them, therefore losing energy.
What is terminal p.d.?
The actual p.d. across the terminals of an e.m.f source when it is connected to a circuit
What happens to e.m.f. and terminal p.d. when no current is flowing across a cell?
They are EQUAL
