Theme B — The Particulate Nature of Matter
B.5.3 Electric Potential Difference — IB Physics HL Revision Notes & Topical Questions
5 min read 10 parts Lesson 44 of 53 1 quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
B.5.3 Electric Potential Difference — IB PHYSICS SL notes: Define potential difference as energy transferred per unit charge and apply V = W/q.Potential difference (p.d.) = the work done per unit charge on moving a positive charge between two points along the path of the current.…
- Source of p.d
- Complete circuit
- Lamp at 6.0 V
- Cell of e.m.f. 1.5 V
- Closed loop
- Kirchhoff's second law
Part 1 of 8Definition
1Potential difference (p.d.)
Potential difference (p.d.) the work done per unit charge on moving a positive charge between two points along the path of the current.
- It is also called voltage.
2Equation
- V = W/q.
- V is the p.d. in volts (V).
- W is the work done or energy transferred in joules (J).
- q is the charge in coulombs (C).
3Volt
- 1 V = 1 J C−1.
4Meaning
- Meaning the p.d. across a component shows how much electrical energy is transferred for each coulomb passing through it.
Part 2 of 8Cells and batteries
Source of p.d.
- Source of p.d. cells or batteries provide the potential difference in a d.c. circuit.
Terminals
- Terminals each cell has a positive terminal (high potential) and a negative terminal (low potential).
Battery
- Battery a collection of cells arranged positive to negative.
Complete circuit
- Complete circuit joining both terminals with a conducting loop lets electrons flow from negative to positive.
Energy
- Energy electrons gain electrical potential energy in the cell and transfer some to the metal ions in the wire.
Part 3 of 8Voltage across components
Voltage across components
Lamp at 6.0 V
- Lamp at 6.0 V each coulomb transfers 6.0 J, mainly to thermal energy and light.
Cell of e.m.f. 1.5 V
- Cell of e.m.f. 1.5 V each coulomb passing through it gains 1.5 J.
Closed loop
- Closed loop the energy given to charge by sources equals the energy transferred by components, so the sum of the e.m.f.s equals the sum of the p.d.s.
Kirchhoff's second law
- Kirchhoff's second law this statement of energy conservation is the second law.
Series circuit
- Series circuit the p.d.s across the components add up to the supply p.d.
Parallel branches
- Parallel branches the p.d. across each branch equals the supply p.d.
Part 4 of 8Combining relations
Combining relations
Energy
- W = qV, and since q = It, W = VIt for a steady current.
Power
- P = W/t = VI.What the symbols mean: P = power (W = J s−1) · W or E = work done / energy transferred (J) · t = time (s) · F = force (N) · v = velocity (m s−1)
Kinetic energy
- Kinetic energy a charge q accelerated from rest through V gains qV = ½mv2, as in an electron gun.
Lighter particles
- Lighter particles they reach a higher speed, so electrons are much faster than protons accelerated through the same p.d.
Voltmeter
- Voltmeter it measures the p.d. between the two points it is attached to, connected in parallel.
Reference
- Reference potential is measured relative to a zero, usually the negative terminal or earth;
- only differences matter.
Part 5 of 8The electronvolt
Electronvolt (eV)
Electronvolt (eV) the energy needed to move an electron through a potential difference of one volt.
Why used
- Why used microscopic particle energies are very small in joules.
Value
- W = qV = eV, so 1 eV = 1.6 × 10−19 J.
Charge of an electron
- Charge of an electron e = 1.6 × 10−19 C is given on the data sheet.
Part 6 of 8Energy conversions
Energy conversions
Lamp
- Lamp electrical energy becomes thermal energy and light.
Motor
- Motor electrical energy becomes kinetic energy and some thermal energy.
Charging battery
- Charging battery electrical energy becomes chemical energy.
Gravity analogy
- Gravity analogy charge moving through a p.d. is like a mass moving through a height difference, with qV corresponding to mgh.
Charge falling through a lamp
- Charge falling through a lamp it falls in potential and gives up energy.
Part 7 of 8Links and definitions in answers
Electric field
- Electric field in a uniform field of strength E the p.d. across a gap d is V = Ed.
Resistance
- V = IR links p.d. to current.
Not energy
- Not energy a small battery with a large p.d. can store less energy than a large battery with a small p.d.
Definition to quote
- Definition to quote the p.d. between two points is the work done per unit charge in moving charge between the points.
- (energy transferred)
230 V
- 230 V each coulomb passing through the supply transfers 230 J.
Distinction
- Distinction p.d. across a component differs from the e.m.f. of a source.
Part 8 of 8More from the specification
1Negative Temperature Coefficient (NTC) Thermistor
- As temperature increases, additional charge carriers are liberated within a semiconductor thermistor,
- causing its electrical resistance to decrease non-linearly on an R-T graph.
2Internal Resistance and Terminal Potential Difference
- Due to internal resistance r within a power source, the terminal potential difference across external circuit components decreases as current measured by an ammeter increases, following V = ε - I r.
3Electrical Resistivity of Conductors
- Resistivity ρ is an intrinsic material property defined by ρ = R A / L (in Ω m),
- which remains constant at a given temperature regardless of conductor dimensions.
4Electric Current and Potential Difference Direction
- An ammeter connected in series measures the rate of charge flow,
- where conventional current flows in the direction of high to low electric potential across a circuit load.
5Negative Temperature Coefficient (NTC) Thermistor
- As temperature increases, additional charge carriers are liberated within a semiconductor thermistor,
- causing its electrical resistance to decrease non-linearly on an R-T graph.
6Internal Resistance and Terminal Potential Difference
- Due to internal resistance r within a power source, the terminal potential difference across external circuit components decreases as current measured by an ammeter increases, following V = ε - I r.
7Electrical Resistivity of Conductors
- Resistivity ρ is an intrinsic material property defined by ρ = R A / L (in Ω m),
- which remains constant at a given temperature regardless of conductor dimensions.
8Electric Current and Potential Difference Direction
- An ammeter connected in series measures the rate of charge flow,
- where conventional current flows in the direction of high to low electric potential across a circuit load.
9Fixed resistor
- Resistor with a resistance that cannot change.
10Conventional current
- Current drawn from the positive to the negative terminal.
11Resistivity
- Property of a material defined by ρ = RA/L.
12Thermistor
- Resistor whose resistance falls as temperature rises.
13Ammeter
- Component that measures current.
14Temperature
- Measure of the average kinetic energy of the particles.
15Internal resistance
- Resistance inside a cell that causes lost p.d.
16Combined resistance
- Single resistance that could replace several resistors.
17Circuit diagram
- Drawing of a circuit using standard symbols.
18Light intensity
- How bright the light falling on a surface is.
Key terms
| Term | Meaning |
|---|---|
| Potential difference | Work done per unit charge on moving a positive charge between two points |
| Volt (V) | Unit of p.d.; 1 J C−1 |
| Electronvolt | Energy gained by an electron moving through 1 V, 1.6 × 10−19 J |
| Battery | Collection of cells arranged positive terminal to negative terminal |
| Electromotive force | Energy per unit charge transferred to electrical energy by a source |
| Kirchhoff's second law | The sum of e.m.f.s equals the sum of p.d.s around a closed loop |
Avoid these mistakes
1
Confusing potential difference with energy — p.d. is energy per coulomb.
2
Forgetting the unit of the volt — it is J C−1.
3
Thinking electrons gain energy from the wire — they gain it in the cell and lose it in components.
4
Using W = qV without converting the charge to coulombs — convert first.
5
Confusing p.d. across a component with the e.m.f. of a source — they are different.
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