POTENTIAL DIFFERENCE (pd) โ also called voltage โ is the energy transferred per unit charge.
Unit: VOLT (V). 1 V = 1 joule per coulomb.
RESISTANCE is the opposition to the flow of current.
Unit: OHM (ฮฉ).
OHM'S LAW:
V = I ร R
V = potential difference (V)
I = current (A)
R = resistance (ฮฉ)
Rearranging:
I = V รท R
R = V รท I
Higher resistance โ lower current for a given pd.
Higher pd โ higher current for a given resistance.
Ohmic Conductors and IโV Graphs
An OHMIC CONDUCTOR (e.g. a resistor at constant temperature):
Current is DIRECTLY PROPORTIONAL to pd.
Resistance stays CONSTANT as current changes.
On an IโV graph:
Straight line through the origin.
Steeper gradient = lower resistance (more current per volt).
MEASURING RESISTANCE:
Ammeter in series + voltmeter in parallel.
R = V รท I
EXAMPLE:
6 V across a resistor, 2 A through it:
R = 6 รท 2 = 3 ฮฉ
Potential Difference in Circuits
SERIES โ pd SPLITS between components:
V_total = Vโ + Vโ + Vโ
Higher resistance โ larger share of pd.
PARALLEL โ pd is the SAME across all branches:
Vโ = Vโ = Vโ = V_supply
EXAMPLE โ series circuit:
Battery = 12 V. Rโ = 4 ฮฉ, Rโ = 8 ฮฉ.
Total R = 12 ฮฉ. I = 12 รท 12 = 1 A.
Vโ = 1 ร 4 = 4 V. Vโ = 1 ร 8 = 8 V. Check: 4 + 8 = 12 V โ
โ ๏ธ Common Mistake
R = V รท I, NOT V ร I. Use the triangle: cover the unknown โ the remaining two show the operation. 'Voltage' is acceptable in everyday speech but the precise term is POTENTIAL DIFFERENCE.
๐ Variables
VPotential difference (V) is measured in volts (V)
ICurrent (I) is measured in amperes (A)
RResistance (R) is measured in ohms (ฮฉ)
๐ Key Equations
V = I ร R
๐ Key Note
V = IR. I = V/R. R = V/I. Ohmic: I โ V, straight IโV line. Series: pd splits (sum = total). Parallel: same pd across each branch. Ammeter in series; voltmeter in parallel.
๐ฏ Matching Activity โ V = IR Calculations
Match each circuit scenario to the correct calculated value. โ drag the symbols on the right to match the component names on the left.
R = 6 ฮฉ
Drop here
I = 0.5 A
Drop here
V = 9 V
Drop here
I doubles
Drop here
Pd doubles for an ohmic conductor โ current proportional to pd
V = 12 V, I = 2 A โ R = 12 รท 2
I = 3 A, R = 3 ฮฉ โ V = 3 ร 3
V = 3 V, R = 6 ฮฉ โ I = 3 รท 6
โฝ FIFA Worked Examples
Resistance Calculation
A component has 12 V across it and 0.4 A through it. Calculate its resistance.
F
R = V รท I
I
V = 12 V, I = 0.4 A
F
R = 12 รท 0.4
A
R = 30 ฮฉ
๐งช Required Practical
๐ฌ RP15 (Physics) โ Measure V and I for different components; calculate resistance using R = V/I.
Know the method, variables, equipment and how to analyse results.
๐ฏ Test Yourself
Question 1 of 2
1. A 6 ฮฉ resistor has 3 A through it. What is the potential difference?
2. On an IโV graph for an ohmic conductor, what does a steeper gradient indicate?
โญ How Well Do You Understand This Topic?
Be honest with yourself โ this helps you know what to revise!
Don't get itGetting thereNailed it!
๐ค Ask Mr Badmus AI
Stuck? Just ask! ๐ฌ
I'll use FIFA for calculations and flag Higher/Triple content clearly.