D.C. circuits: components, networks and transients
Key idea: Read topology before calculating, distinguish component and source behaviour, and use shared-current, shared-p.d., shared-charge and exponential models only in the arrangements where they apply.
Before you start: Current Electricity objective chainElectric Fields objective chain
By the end, you can
- Use standard circuit symbols and interpret electrical topology with correct meter placement.
- Apply resistance and resistivity while explaining component I–V and temperature behaviour microscopically.
- Analyse terminal p.d. and power when a source has internal resistance.
- Solve resistor networks and sensor potential dividers.
- Combine capacitors using shared-charge and shared-potential-difference reasoning.
- Represent capacitor charging and discharging with the correct exponential and time constant.
Starting-point self-check
1. Check your starting point
Attempt all six groups without notes and mark the first diagram, material, source, network, capacitance or transient decision you cannot justify. Use the recorded topic diagnostic above when you want scoring and a personalised repair plan.
Circuit symbols and diagrams 16(a)–(b)
Question 1
Describe a circuit that measures the I–V characteristic of a filament lamp, including source, switch, variable control and both meters.
Check the model response
Connect the source, switch, variable resistor and ammeter in series with the lamp. Connect the voltmeter in parallel across the lamp. Use standard symbols, show junctions unambiguously and place the variable control so current can be changed.
repair
2. Repair the common breaks
Use only the correction matching an error, then retry the corresponding diagnostic.
Circuit symbols and diagrams 16(a)–(b)
Check this idea
Misconception: A circuit diagram must copy the apparatus layout.
Repair: A diagram represents electrical nodes and connections with standard symbols; physical positions are irrelevant.
Check this idea
Misconception: An ammeter belongs across a component and a voltmeter in series.
Repair: An ammeter is series-connected in the measured branch; a voltmeter is parallel-connected across two nodes.
worked example
3. Follow six worked models
Follow how each solution fixes nodes, axes, source boundary, network reduction, shared capacitor quantity or initial condition before calculating.
Circuit symbols and diagrams 16(a)–(b)
Model 1
A student draws an ammeter across a diode and a voltmeter in series. Diagnose and correct both connections.
Check the model response
An ideal ammeter has negligible resistance and must be in series with the diode branch; placing it across the diode risks a near short circuit. A voltmeter has very high resistance and must be in parallel across the two points whose p.d. is required.
guided practice
4. Guided practice
Use each hint only to select the correct topology, material model, combination rule or exponential.
Circuit symbols and diagrams 16(a)–(b)
Question 1
Where should a voltmeter be placed to measure the p.d. across an LDR in a divider?
Hint: A voltmeter compares two node potentials.
Check the model response
Connect it in parallel between the two LDR terminals.
independent practice
5. Independent practice
Solve without repair notes and state graph axes, ideal-meter assumptions, source model and RC initial/final conditions.
Circuit symbols and diagrams 16(a)–(b)
Question 1
State the symbols/components named by Topic 16 and explain the difference between a diagram's topology and physical layout.
Check the model response
Be able to use sources, switches, fixed and variable resistors, ammeters, voltmeters, lamps, thermistors, LDRs, diodes and capacitors, plus other syllabus components. A circuit diagram records nodes and connections using symbols; positions and wire shapes need not match the apparatus.
Practice exit check
6. Practice assessment
Use this as extra closed-book practice, then complete the separate recorded assessment in your plan.
Circuit symbols and diagrams 16(a)–(b)
Question 1
Draw verbally a circuit to measure the resistance of an NTC thermistor at several temperatures and state correct meter placement.
Check the model response
Use a source, switch, current-limiting variable resistor and ammeter in series with the NTC; put a voltmeter in parallel across the NTC. Use standard symbols and measure temperature independently, limiting current to reduce self-heating.
Re-test practice
7. Delayed re-test practice
Return after at least three days and solve these fresh contexts without reopening earlier responses. The recorded plan enforces the delay and uses a separate re-test family for selected-response skill-group evidence.
Circuit symbols and diagrams 16(a)–(b)
Question 1
State why an ideal ammeter is series-connected and an ideal voltmeter parallel-connected.
Check the model response
An ammeter measures branch current and has zero ideal resistance, so it belongs in that branch. A voltmeter measures a potential difference between two nodes and has infinite ideal resistance, so it connects across them without drawing current.