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Module 4: Electrons, waves and photons

The electrons, waves and photons module is all taught in year 12 and forms half of Exploring Physics.  The topic builds on your GCSE knowledge of electricity and waves and it is essential that you have a good grasp of these before starting the A Level course. It is a good idea to visit the Year 10 and Year 11 GCSE pages and go over the electricity and wave topics in both of these years.


The electrons, waves and photons module is split in to 5 sub-modules: 

Image by Will Porada

4.1 & 2 Charge, current, power and resistance 

By the end of this topic you should be able to:​

  • Define what is meant by electrical current (including the difference between electron flow and conventional current) and use the equation linking current, charge and time

  • Describe what is meant by charge and how this is measured and conserved in circuits.

  • Describe the atomic structure of a metal and how this enables a flow of electric current

  • Understand what is meant by mean drift velocity and calculate this for a wire

  • Describe the difference between conductors, semiconductors and insulators

  • Recognise and draw circuit symbols and construct accurate circuit diagrams using these

  • Describe the similarities and differences between potential difference (p.d.) and electromotive force (e.m.f.) as ways of measuring voltage

  • Use the equations linking work done or energy transferred, voltage and charge

  • Link the equation for kinetic energy to energy transferred in circuits for electrons and other charged particles

  • Define resistance and Ohm's law and calculate this from current and voltage

  • Draw graphs and describe the relationship between current and voltage for a resistor, filament lamp, diode and light emitting diode (LED) and explain how you would obtain these results experimentally.

  • Describe how resistance varies with a change in external factors for a light dependent resistor and a thermistor

  • Describe the factors that influence the resistance of a wire

  • Describe what is meant by resistivity of a material, how this can be found experimentally and use the equation to calculate this.

  • Calculate electrical power in circuits from voltage, current and resistance and energy transferred from voltage, current and time.

4.3 Electrical circuits

4.3 Advanced Electrical circuits

Image by John Barkiple

By the end of this topic you should be able to:​

  • State Kirchhoff's first and second law and apply these to analysis of circuits

  • Calculate the total resistance of a circuit with resistors in series and parallel. 

  • Analyse circuits with more than one source of e.m.f.

  • Describe what is meant by internal resistance in terms of terminal p.d. and "lost volts", describe how internal resistance of a cell can be obtained experimentally and calculate this in circuits 

  • Describe how a potential divider works to change voltage split with components such as LDRs and thermistors. Use the potential divider equations in circuit analysis and describe how you could build a circuit for a specific function using the ideas of a potential divider.

4.4 Waves

4.4 Waves

By the end of this topic you should be able to:​

  • Describe the difference between a longitudinal and transverse wave and describe how these are represented graphically

  • Define the terms displacement, amplitude, wavelength, period, frequency and wave speed.

  • Describe how you could use an oscilloscope to determine the frequency of a wave

  • Calculate frequency from time period and wave speed from frequency and wavelength

  • Define what is meant by intensity of a wave and how this links to amplitude

  • State what is meant by the electromagnetic spectrum and state properties which are common to all of these forms of radiation and the order of magnitude of individual forms of radiation within the spectrum.

  • Define the law of reflection and sketch ray diagrams to show this. 

  • Describe how light is refracted, sketch ray diagrams to show this and describe how you would show this experimentally

  • Describe what is meant by the refractive index and how this links to the angle of incidence. Calculate this from materials knowing the speed of light in a vacuum and the speed of light in the material

  • Explain how total internal reflection occurs and how this can be shown experimentally, link this to the "critical angle".

  • Describe how waves can become polarised and explain how this can be shown experimentally for microwaves and light

  • State the principle of superposition of waves, including how this can be demonstrated graphically, and explain how this effect can be demonstrated using sound, light and microwaves. 

  • State the difference between constructive and destructive interference in terms of path difference and phase difference

  • Describe Young's double-slit experiment as evidence for interference of light waves, and describe how this can be used to find the wavelength of light

  • Explain the similarities and differences between a progressive wave and a stationary wave 

  • State features of stationary waves including nodes and antinodes and why these form in relation to wavelength.

  • Draw stationary wave patterns formed on a stretched spring and air columns in closed and open tubes

  • Describe how the speed of sound in air can be found experimentally using stationary waves

  • Describe the relationship between musical harmonics, fundamental frequencies and stationary waves

4.5 Quantum Physics

4.5 & 6.4 Particle and Quantum Physics

Image by Shahadat Rahman

By the end of this topic you should be able to:​

  • Describe Rutherford's alpha particle scattering experiment as evidence for the nucleus

  • Describe the parts of the modern atomic model including relative sizes

  • Define the terms; proton number, nucleon number and isotopes

  • Describe the properties of the forces acting within a nucleus

  • Calculate the radius and densities of nuclei

  • Describe the difference between particles and antiparticles and name examples of these

  • Describe and give examples and properties of hadrons and leptons

  • Describe the quark model of hadrons including up, down and strange quarks and the arrangements in protons and neutrons

  • Describe the photon model of electromagnetic radiation

  • Calculate the energy of a photon using Planck constant and frequency or the speed of light and wavelength

  • Define the electronvolt as a unit of energy

  • Describe how the Planck constant can be found experimentally using different colour LEDs  

  • Describe the photoelectric effect and how this can be shown experimentally using a gold-leaf electroscope. Describe the one-to-one interaction between photons and electrons that happens in this effect

  • Use and explain Einstein's photoelectric equation to help explain the photoelectric effect, including the terms work function and threshold frequency. 

  • Describe why the maximum kinetic energy of a photoelectron is independent of intensity of incident radiation but the rate of emission is dependent on the radiation intensity 

  • Explain and give evidence to support why waves and particles can behave both as waves and particles (wave-particle duality) 

  • Describe experimentally how electrons can behave like waves with electrons diffracting as they pass through a thin slice of polycrystalline graphite

  • Use the de Broglie equation to calculate the wavelength of a particle based on the Planck constant and the particle's momentum

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