Unit 2: Waves and Electricity

Understand the terms amplitude, frequency, period, speed and wavelength.

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

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

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

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

Be able to use the wave equation v = fλ.

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

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

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

Boundary: use the formula and units given in the question, show the substitution and interpret the result; the calculation alone is not the conclusion.

Be able to describe longitudinal waves in terms of pressure variation and the displacement of molecules.

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

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

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

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

Be able to describe transverse waves.

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

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

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

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

Be able to draw and interpret graphs representing transverse and longitudinal waves including standing/stationary waves.

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

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

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

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

CORE PRACTICAL 4: Determine the speed of sound in air using a 2-beam oscilloscope, signal generator, speaker and microphone.

Use - core practical 4 - speed of sound in air to connect the rule to the data and decision in the question.

This matters because - core practical 4 - speed of sound in air determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - core practical 4 - speed of sound in air to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Core Practical 4 - speed of sound in air is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Know and understand what is meant by wavefront, coherence, path difference, superposition, interference and phase.

Use - wavefronts, coherence and interference to connect the rule to the data and decision in the question.

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

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

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

Be able to use the relationship between phase difference and path difference.

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

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

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

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

Know what is meant by a standing or stationary wave, understand how it is formed, and identify nodes and antinodes.

Use - standing waves, nodes and antinodes to connect the rule to the data and decision in the question.

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

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

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

Use v = √(T/μ) for the speed of a transverse wave on a string.

Use - speed of a transverse wave on a string to connect the rule to the data and decision in the question.

This matters because - speed of a transverse wave on a string determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - speed of a transverse wave on a string to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Speed of a transverse wave on a string is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

CORE PRACTICAL 5: Investigate how length, tension and mass per unit length affect the frequency of a vibrating string or wire.

Use - core practical 5 - vibrating string frequency to connect the rule to the data and decision in the question.

This matters because - core practical 5 - vibrating string frequency determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - core practical 5 - vibrating string frequency to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Core Practical 5 - vibrating string frequency is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Use I = P/A for the intensity of radiation.

Use - intensity of radiation to connect the rule to the data and decision in the question.

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

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

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

Use n1 sin θ1 = n2 sin θ2 at a boundary between two media and refractive index n = c/v.

Use - refraction at a boundary to connect the rule to the data and decision in the question.

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

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

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

Calculate critical angle using sin C = 1/n.

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

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

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

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

Be able to predict whether total internal reflection will occur at an interface.

Use - total internal reflection to connect the rule to the data and decision in the question.

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

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

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

Understand how to measure the refractive index of a solid material.

Use - measuring refractive index to connect the rule to the data and decision in the question.

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

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

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

Understand what is meant by plane polarisation.

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

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

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

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

Understand what is meant by diffraction and use Huygens’ construction to explain what happens to a wave when it meets a slit or an obstacle.

Use - diffraction and huygens’ construction to connect the rule to the data and decision in the question.

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

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

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

Be able to use nλ = dsinθ for a diffraction grating.

Use - diffraction grating equation to connect the rule to the data and decision in the question.

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

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

Boundary: use the formula and units given in the question, show the substitution and interpret the result; the calculation alone is not the conclusion.

CORE PRACTICAL 6: Determine the wavelength of light from a laser or other light source using a diffraction grating.

Use - core practical 6 - wavelength using diffraction grating to connect the rule to the data and decision in the question.

This matters because - core practical 6 - wavelength using diffraction grating determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - core practical 6 - wavelength using diffraction grating to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Core Practical 6 - wavelength using diffraction grating is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Understand how diffraction experiments provide evidence for the wave nature of electrons.

Use - electron diffraction evidence to connect the rule to the data and decision in the question.

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

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

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

Use the de Broglie equation λ = h/p.

Use - de broglie wavelength to connect the rule to the data and decision in the question.

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

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

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

Understand that waves can be transmitted and reflected at an interface between media.

Use - transmission and reflection at boundaries to connect the rule to the data and decision in the question.

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

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

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

Understand how a pulse-echo technique can provide information about the position of an object and how the amount of information obtained may be limited by the wavelength of the radiation or by the duration of pulses.

Use - pulse-echo techniques to connect the rule to the data and decision in the question.

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

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

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

Understand how the behaviour of electromagnetic radiation can be described in terms of a wave model and a photon model, and how these models developed over time.

Use - wave and photon models of em radiation to connect the rule to the data and decision in the question.

This matters because - wave and photon models of em radiation determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply - wave and photon models of em radiation to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: - Wave and photon models of EM radiation is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

Be able to use the equation E = hf, that relates the photon energy to the wave frequency.

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

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

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

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

Understand that the absorption of a photon can result in the emission of a photoelectron.

Use - photon absorption and photoelectron emission to connect the rule to the data and decision in the question.

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

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

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

Understand threshold frequency and work function and use the photoelectric equation hf = φ + ½mvmax².

Use - threshold frequency and work function to connect the rule to the data and decision in the question.

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

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

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

Be able to use the electronvolt (eV) to express small energies.

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

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

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

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

Understand how the photoelectric effect provides evidence for the particle nature of electromagnetic radiation.

Use - photoelectric effect evidence to connect the rule to the data and decision in the question.

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

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

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

Understand atomic line spectra in terms of transitions between discrete energy levels and understand how to calculate the frequency of radiation that could be emitted or absorbed in a transition between energy levels.

Use - atomic line spectra and energy levels to connect the rule to the data and decision in the question.

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

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

Boundary: - Atomic line spectra and energy levels is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.

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.