Electricity and Circuits
Key formulas and rules for analysing series and parallel circuits.
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Questions Covered in This Set
10 cards to master
State Ohm's law (three rearrangements)
V = IR, I = V/R, R = V/I
What are the three power formulas?
P = VI, P = I²R, P = V²/R
Formulas for charge and energy
Q = It (coulombs) and E = Pt (joules)
Three rules for a series circuit
Current is the same everywhere; voltages add to the supply; R_total = R₁ + R₂ + …
Three rules for a parallel circuit
Voltage is the same across each branch; currents add; 1/R_total = 1/R₁ + 1/R₂
Why is total parallel resistance smaller than the smallest branch?
Extra paths make it easier for charge to flow; for two equal resistors R_total = R/2
I–V graph shape for an ohmic conductor
A straight line through the origin (constant resistance)
I–V graph for a filament lamp and a diode
Lamp curves (resistance rises as it heats); diode conducts in one direction only
How are ammeters and voltmeters connected?
Ammeters in series (measure current through); voltmeters in parallel (measure p.d. across)
9 V battery with 2 Ω and 4 Ω in series — find I and each voltage
R_total = 6 Ω, I = 1.5 A, V = 3 V and 6 V (sum = 9 V)
