Key term
CCEA A-Level Physics 1210
Physical Quantities, Scalars and Vectors
Moments and Equilibrium
Linear Motion and Dynamics
Newton's Laws of Motion
Linear Momentum and Impulse
Work, Energy and Power
Current, Charge and Potential Difference
Resistance and Resistivity
Topic overviewResistance and Ohm's lawOhmic and non-ohmic behaviourResistors in series and in parallelInvestigating current, voltage and resistance in series and parallel circuitsElectrical power and energy in resistive circuitsResistivity and the equation R = ρl/AMeasuring the resistivity of a metalCurrent–voltage characteristics of a conductor, a lamp and a diodeResistance, temperature and superconductivity
Internal Resistance and Potential Dividers
Topic overviewInternal resistance and terminal potential differenceConsequences of internal resistance for external circuitsMeasuring electromotive force and internal resistanceThe potential divider and variable outputPotential dividers in lighting and heating control circuitsLoaded potential dividers and output voltage calculations
Waves
Refraction
Lenses
Superposition, Interference and Diffraction
Topic overviewSuperposition of wavesStanding waves, nodes and antinodesStanding waves on stretched stringsStanding waves in a pipe closed at one endMeasuring the speed of sound with a resonance tubeConditions for observable interferencePath difference and phase differenceYoung's double slitDiffraction at a single slitThe diffraction grating
Quantum Physics
Wave-Particle Duality
Astronomy
Practical Skills and Data Analysis
Topic overviewChoosing and using measuring instrumentsPrecision, accuracy and recording measurementsUsing the cathode ray oscilloscope to measure voltage and frequencyTables, graphs and presenting resultsLinearising a relationship and using the gradientAbsolute and percentage uncertaintyCombining uncertainties and uncertainty on a graphRandom and systematic error, reliability and refining an experiment
Deformation of Solids
Thermal Physics
Topic overviewBoyle's law, Charles's law and the pressure lawThe ideal gas equation pV = nRTThe Avogadro constant, the mole and pV = NkTInternal energy and the distribution of molecular energyThe kinetic theory equation pV = ⅓Nm⟨c²⟩Average molecular kinetic energy and temperatureAbsolute zero and the kelvin scaleSpecific heat capacity and the electrical method
Uniform Circular Motion
Simple Harmonic Motion
Topic overviewDefining simple harmonic motion and a = −ω²xDisplacement, velocity and acceleration: x = A cos ωtThe simple pendulum and T = 2π√(l/g)The loaded spiral spring and T = 2π√(m/k)SHM graphs and finding velocity from a gradientFree vibrations, forced vibrations and resonanceDamping: light, critical and over-damping
The Nucleus and Radioactive Decay
Topic overviewAlpha-particle scattering and the nuclear atomNuclear radius and nucleon numberThe density of nuclear matterAlpha, beta and gamma radiation: nature, penetration and rangeNuclear equations and changes in nucleon and proton numberThe random and exponential nature of radioactive decayActivity, the decay constant and A = −λNExponential decay calculations with A = A₀e^(−λt)Half-life and measuring it
Nuclear Energy, Fission and Fusion
Gravitational Fields
Electric Fields
Capacitors
Magnetic Fields
Charged Particles and Accelerators
Wave-Particle Duality
Electron diffraction
- 3 things to know
- Unit AS 2
Overview
Recall questions on the electron diffraction tube and what is seen on its screen, why a ring pattern rather than spots appears, why a crystal is used rather than a slit, how the ring size changes with the accelerating voltage and how that supports de Broglie, why a cricket ball cannot be diffracted, and why the tube must be evacuated.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
In an electron diffraction tube, why is a ring pattern produced rather than a set of separate spots?
Key term
What happens to the diameters of the rings when the accelerating voltage in an electron diffraction tube is increased?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is electron diffraction?
Model answer
Electron diffraction is the spreading and interference of a beam of electrons passing through a regular structure such as a thin crystal, producing a pattern that only a wave can account for.
- 2
Describe the electron diffraction tube experiment.
Model answer
In an evacuated tube, electrons from a heated filament are accelerated through a large potential difference and directed at a very thin sheet of polycrystalline graphite, and the electrons that pass through strike a fluorescent screen at the far end.
- 3
What is seen on the fluorescent screen in an electron diffraction tube?
Model answer
A bright central spot surrounded by concentric bright and dark rings, exactly like the pattern light produces when it is diffracted.
- 4
Why is a ring pattern produced rather than a set of separate spots?
Model answer
The graphite is made of very many tiny crystals lying in all possible orientations, so the diffracted directions occur at the same angle all the way round the beam and each order forms a complete circle.
- 5
What does the electron diffraction pattern show about electrons?
Model answer
It shows that electrons, which have mass and charge and were regarded as particles, also show wave behaviour, since only waves can produce a diffraction pattern.
- 6
Why is a crystal used as the diffracting object for electrons rather than a slit?
Model answer
Noticeable diffraction requires a gap comparable with the wavelength, and the electron wavelength of about 10⁻¹⁰ m matches the spacing between atoms in a crystal but is far smaller than any slit that could be cut.
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