2.4 - Electric Circuits

Understand current as the rate of flow of charge and use I = ΔQ/Δt.

Use - electric current to connect the rule to the data and decision in the question.

This matters because - electric current determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - electric current to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Electric current is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Use potential difference V = W/Q.

Use - potential difference to connect the rule to the data and decision in the question.

This matters because - potential difference determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - potential difference to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Potential difference is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand resistance R = V/I and Ohm's law as the special case I ∝ V at constant temperature.

Use - resistance and ohm’s law to connect the rule to the data and decision in the question.

This matters because - resistance and ohm’s law determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - resistance and ohm’s law to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Resistance and Ohm’s law is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

(a) understand how the distribution of current in a circuit is a consequence of charge conservation (b) understand how the distribution of potential differences in a circuit is a consequence of energy conservation.

Use - current and p.d. distributions in circuits to connect the rule to the data and decision in the question.

This matters because - current and p.d. distributions in circuits determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - current and p.d. distributions in circuits to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Current and p.d. distributions in circuits is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Be able to derive the equations for combining resistances in series and parallel using the principles of charge and energy conservation, and be able to use these equations.

Use - combining resistances in series and parallel to connect the rule to the data and decision in the question.

This matters because - combining resistances in series and parallel determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - combining resistances in series and parallel to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Combining resistances in series and parallel is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Use P = VI and W = VIt, and derive and use P = I²R and P = V²/R.

Use - electrical power and energy to connect the rule to the data and decision in the question.

This matters because - electrical power and energy determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - electrical power and energy to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Electrical power and energy is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Sketch, recognise and interpret current–potential-difference graphs for ohmic conductors, filament bulbs, thermistors and diodes.

Use - i-v graphs for circuit components to connect the rule to the data and decision in the question.

This matters because - i-v graphs for circuit components determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - i-v graphs for circuit components to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - I-V graphs for circuit components is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Use R = ρl/A for the resistance of a uniform conductor.

Use - resistivity to connect the rule to the data and decision in the question.

This matters because - resistivity determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - resistivity to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Resistivity is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

CORE PRACTICAL 7: Determine the electrical resistivity of a material.

Use - core practical 7 - electrical resistivity to connect the rule to the data and decision in the question.

This matters because - core practical 7 - electrical resistivity determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - core practical 7 - electrical resistivity to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Core Practical 7 - electrical resistivity is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Be able to use I = nqvA to explain the large range of resistivities of different materials.

Use - conduction model and resistivity to connect the rule to the data and decision in the question.

This matters because - conduction model and resistivity determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - conduction model and resistivity to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Conduction model and resistivity is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand how the potential along a uniform current-carrying wire varies with the distance along it.

Use - potential along a current-carrying wire to connect the rule to the data and decision in the question.

This matters because - potential along a current-carrying wire determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - potential along a current-carrying wire to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Potential along a current-carrying wire is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand the principles of a potential divider circuit and understand how to calculate potential differences and resistances in such a circuit.

Use - potential divider circuits to connect the rule to the data and decision in the question.

This matters because - potential divider circuits determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - potential divider circuits to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Potential divider circuits is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Be able to analyse potential divider circuits where one resistance is variable including thermistors and light dependent resistors (LDRs).

Use - variable-resistance potential dividers to connect the rule to the data and decision in the question.

This matters because - variable-resistance potential dividers determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - variable-resistance potential dividers to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Variable-resistance potential dividers is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Know the definition of electromotive force (e.m.f.) and understand what is meant by internal resistance and know how to distinguish between e.m.f. and terminal potential difference.

Use - e.m.f. and internal resistance to connect the rule to the data and decision in the question.

This matters because - e.m.f. and internal resistance determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - e.m.f. and internal resistance to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - E.m.f. and internal resistance is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

CORE PRACTICAL 8: Determine the e.m.f. and internal resistance of an electrical cell.

Use - core practical 8 - e.m.f. and internal resistance to connect the rule to the data and decision in the question.

This matters because - core practical 8 - e.m.f. and internal resistance determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - core practical 8 - e.m.f. and internal resistance to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Core Practical 8 - e.m.f. and internal resistance is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand how changes of resistance with temperature may be modelled in terms of lattice vibrations and number of conduction electrons and understand how to apply this model to metallic conductors and negative temperature coefficient thermistors.

Use - temperature effects on resistance to connect the rule to the data and decision in the question.

This matters because - temperature effects on resistance determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - temperature effects on resistance to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Temperature effects on resistance is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand how changes of resistance with illumination may be modelled in terms of the number of conduction electrons and understand how to apply this model to LDRs.

Use - illumination effects on ldr resistance to connect the rule to the data and decision in the question.

This matters because - illumination effects on ldr resistance determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - illumination effects on ldr resistance to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Illumination effects on LDR resistance is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.