Theme B — The Particulate Nature of Matter
B.5.1 Circuit Diagrams — IB Physics HL Revision Notes & Topical Questions
5 min read 10 parts Lesson 42 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.5.1 Circuit Diagrams — IB PHYSICS SL notes: Draw and interpret standard circuit diagrams using circuit symbols and place ammeters and voltmeters correctly.Circuit diagram — a simplified map of how the components of a circuit are connected.Symbols — they are universally recognis…
- Wire resistance
- Energy source
- Closed path
- Data booklet
- Ideal meters
- Real meters
Section 1 of 10Purpose of circuit diagrams
Circuit diagram
- Circuit diagram a simplified map of how the components of a circuit are connected.
Symbols
- Symbols they are universally recognised by scientists in any language.
Layout
- Layout the real layout of wires is ignored;
- wires are straight lines with right-angle corners and the length on paper means nothing.
Wire resistance
- Wire resistance a wire is assumed to have zero resistance unless the diagram says otherwise.
Position
- Position some components must be in a certain position relative to the others to work.
Section 2 of 10What a diagram must include
What a diagram must include
Energy source
- Energy source a source of potential difference, such as a cell, battery or power supply.
Closed path
- Closed path charge must flow in a complete loop; an open switch breaks the loop and no steady current flows.
Components
- Components drawn with the correct circuit symbol.
- Sensors that respond to the environment, such as an LDR or thermistor.
- Meters that measure a value, such as an ammeter or voltmeter.
- Devices that transfer electrical energy, such as an LED or lamp.
Section 3 of 10Standard symbols and their roles
| Component | Role |
|---|---|
| Cell or battery | Converts chemical energy to electrical energy; the longer line is positive; a battery is two or more cells in series |
| Switch | Closed switch turns the circuit on, open switch turns it off |
| Fixed resistor | Limits the current by transforming electrical energy into other stores such as thermal energy |
| Variable resistor | A slider changes its resistance; greater resistance means less current |
| LDR | Resistance falls as light intensity rises |
| Thermistor | Resistance falls as temperature rises |
| Potentiometer | A resistor with a sliding contact forming an adjustable voltage divider |
| Lamp | Emits light by heating a filament in a glass cover |
| LED | Emits light when current passes; a diode conducts in one direction only |
| Heating element | Converts electrical energy to thermal energy through resistance |
| Motor | Converts electrical energy to mechanical energy |
| Earth | Connection to the ground that allows an instant discharge if an appliance malfunctions |
Fuse
- Fuse a rectangle with a line along it.
Junction
- Junction a dot marks where wires join; wires that cross without a dot are not connected.
Data booklet
- Data booklet it lists the symbols, so you must identify and draw them correctly rather than memorise them.
Section 4 of 10Connecting meters
Connecting meters
Ammeter
- Ammeter measures the current and is always connected in series.
- An ideal ammeter has zero resistance, so it takes no energy and does not alter the current.
Voltmeter
- Voltmeter measures the potential difference and is always connected in parallel across the component.
- An ideal voltmeter has infinite resistance, so no current passes through it.
Ideal meters
- Ideal meters unless stated otherwise, exam questions use ideal meters.
Real meters
- Real meters a real voltmeter has very large but finite resistance and a real ammeter very small but non-zero resistance,
- causing small systematic errors.
Test circuit for a resistor
- Test circuit for a resistor cell, switch, variable resistor, resistor and ammeter in one series loop, with the voltmeter across the resistor only.
Section 5 of 10Direction of current
Conventional current
- Conventional current it is drawn flowing from the positive terminal of the source, round the circuit, to the negative terminal.
Electrons
- Electrons in metals they move the opposite way.
Arrows
- Arrows diagrams always show conventional current.
Diode and LED
- Diode and LED the symbol points in the direction of conventional current.
Section 6 of 10Reading and drawing a diagram
1
To read a diagram, find the source and trace the paths the current may take.
2
A split at a junction means a parallel arrangement; a single path means series.
3
To draw one, build the main series loop first.
4
Add each parallel branch.
5
Place the meters last.
6
Use a ruler, keep symbols clearly separated and label values.
Marks lost
- Marks lost gaps in wires, meters of the wrong type and ambiguous symbols.
Redrawing
- Redrawing a different layout with the same connections is the same circuit.
Section 7 of 10Switch questions
1Switch in parallel with a lamp
- Switch in parallel with a lamp closing it shorts the lamp, so the lamp goes out and the rest of the circuit carries more current.
2Check
- Check every component must be in a closed loop with a source.
Section 8 of 10More from the specification
More from the specification
Ohm's Law and I-V Graphs
- Ohm's law states that current through a conductor is directly proportional to potential difference across it at constant temperature;
- on an I-V graph, the inverse gradient represents resistance.
Sensory Components and Temperature Effects
- In a thermistor,
- increasing temperature causes resistance to decrease exponentially,
- whereas in a metal filament lamp, heating increases resistance due to increased electron-lattice scattering.
Resistivity and Combined Resistance
- Wire resistance is given by the equation R = ρ·L / A,
- where ρ is material resistivity; combining resistors in series increases overall combined resistance,
- (Rtotal = R₁ + R₂)
- while parallel arrangements decrease combined resistance.
- (1/Rtotal = 1/R₁ + 1/R₂)
Resistivity
- Property of a material defined by ρ = RA/L.
Combined resistance
- Single resistance that could replace several resistors.
Section 9 of 10Key terms
| Term | Meaning |
|---|---|
| Circuit diagram | Diagram using standard symbols to show how components are connected |
| Ammeter | Meter that measures current, connected in series |
| Voltmeter | Meter that measures potential difference, connected in parallel |
| Conventional current | Flow of positive charge from the positive terminal to the negative terminal |
| Ideal meter | Meter that does not alter the circuit it measures |
| Closed circuit | Complete loop with a source in which current can flow |
Section 10 of 10Exam technique
1
Connecting a voltmeter in series — it goes in parallel.
2
Drawing electron flow as the current direction — conventional current is positive to negative.
3
Drawing crossing wires with a dot when they are not joined — a dot means a connection.
4
Drawing wires with gaps or curves — use straight lines with neat corners.
5
Placing an ammeter across a component — it must be in series.
Marked practiceQuizzes for this lesson
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