What is the ultraviolet catastrophe?

The prediction by classical physics that a black body would radiate infinite energy at short wavelengths, which contradicted experimental observations.

Define black-body radiation.

Electromagnetic radiation emitted by an idealised object that absorbs all incident radiation and emits radiation dependent only on its temperature.

What did the Rayleigh-Jeans law predict about the intensity of black-body radiation as wavelength decreases?

That the intensity should increase without limit as wavelength decreases.

How does the experimentally observed black-body radiation spectrum differ from classical predictions at short wavelengths?

Experimental observations show that intensity reaches a peak at a certain wavelength and then decreases at shorter wavelengths, rather than increasing without limit.

How did Planck resolve the ultraviolet catastrophe?

By proposing that energy is emitted and absorbed in discrete packets called quanta, rather than continuously.

State the relationship between the energy of a quantum and the frequency of radiation according to Planck.

The energy of each quantum is proportional to the frequency of the radiation, given by E = hf.

AQA A-Level Physics 7408

Measurements and Their Errors

Topic overview Use of SI units and their prefixes Limitation of physical measurements Estimation of physical quantities

Particles and Radiation

Topic overview Constituents of the atom Stable and unstable nuclei Particles, antiparticles and photons Particle interactions Classification of particles Quarks and antiquarks Applications of conservation laws The photoelectric effect Collisions of electrons with atoms Energy levels and photon emission Wave-particle duality

Waves

Topic overview Progressive waves Longitudinal and transverse waves Principle of superposition of waves and formation of stationary waves Interference Diffraction Refraction at a plane surface

Mechanics and Materials

Topic overview Scalars and vectors Moments Motion along a straight line Projectile motion Newton's laws of motion Momentum Work, energy and power Conservation of energy Bulk properties of solids The Young modulus

Electricity

Topic overview Basics of electricity Current–voltage characteristics Resistivity Circuits Potential divider Electromotive force and internal resistance

Further Mechanics and Thermal Physics

Topic overview Circular motion Simple harmonic motion (SHM)Simple harmonic systems Forced vibrations and resonance Thermal energy transfer Ideal gases Molecular kinetic theory model

Fields and Their Consequences

Topic overview Fields Newton's law Gravitational field strength Gravitational potential Orbits of planets and satellites Coulomb's law Electric field strength Electric potential Capacitance Parallel plate capacitor Energy stored by a capacitor Capacitor charge and discharge Magnetic flux density Moving charges in a magnetic field Magnetic flux and flux linkage Electromagnetic induction Alternating currents Transformers

Nuclear Physics

Topic overview Rutherford scattering α, β and γ radiation Radioactive decay Nuclear instability Nuclear radius Mass and energy Induced fission Safety aspects

AstrophysicsOptional topic

Topic overview Astronomical telescope consisting of two converging lenses Reflecting telescopes Single dish radio telescopes, I-R, U-V and X-ray telescopes Advantages of large diameter telescopes Classification by luminosity Absolute magnitude, M Classification by temperature, black-body radiation Principles of the use of stellar spectral classes The Hertzsprung-Russell (HR) diagram Supernovae, neutron stars and black holes Doppler effect Hubble's law Quasars Detection of exoplanets

Medical PhysicsOptional topic

Engineering PhysicsOptional topic

Topic overview Concept of moment of inertia Rotational kinetic energy Rotational motion Torque and angular acceleration Angular momentum Work and power First law of thermodynamics Non-flow processes The p–V diagram Engine cycles Second Law and engines Reversed heat engines

Turning Points in PhysicsOptional topic

Topic overview Cathode rays Thermionic emission of electrons Specific charge of the electron Principle of Millikan's determination of the electronic charge, e Newton's corpuscular theory of light Significance of Young's double slits experiment Electromagnetic waves The discovery of photoelectricity Wave–particle duality Electron microscopes The Michelson-Morley experiment Einstein's theory of special relativity Time dilation Length contraction Relativistic mass and energy

ElectronicsOptional topic

Topic overview MOSFET (metal-oxide semiconducting field-effect transistor)Zener diode Photodiode Hall effect sensor Difference between analogue and digital signals LC resonance filters The ideal operational amplifier Inverting amplifier configuration Non-inverting amplifier configuration Summing amplifier configuration Real operational amplifiers Combinational logic Sequential logic Astables Principles of communication systems Transmission media Time-division multiplexing Amplitude (AM) and frequency modulation (FM) techniques

Turning Points in Physics

The discovery of photoelectricity

4 things to know
Paper 3, section B

Overview

The ultraviolet catastrophe and black-body radiation, Planck's quantum, why classical wave theory failed to explain photoelectric emission, and Einstein's photon explanation and photoelectric equation.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

What was the ultraviolet catastrophe, how did Planck resolve it, and how does the energy of each packet depend on frequency?

Numbers

What is the work function, and how does a photon interact with an electron?

Numbers

What was de Broglie's hypothesis, and what did Einstein show about light?

Numbers

When is λ = h/√(2meV) used, how does electron diffraction show wave behaviour, and what happens to the rings as voltage rises?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the ultraviolet catastrophe?
Model answer
The prediction by classical physics that a black body would radiate infinite energy at short wavelengths, which contradicted experimental observations.
2
Define black-body radiation.
Model answer
Electromagnetic radiation emitted by an idealised object that absorbs all incident radiation and emits radiation dependent only on its temperature.
3
What did the Rayleigh-Jeans law predict about the intensity of black-body radiation as wavelength decreases?
Model answer
That the intensity should increase without limit as wavelength decreases.
4
How does the experimentally observed black-body radiation spectrum differ from classical predictions at short wavelengths?
Model answer
Experimental observations show that intensity reaches a peak at a certain wavelength and then decreases at shorter wavelengths, rather than increasing without limit.
5
How did Planck resolve the ultraviolet catastrophe?
Model answer
By proposing that energy is emitted and absorbed in discrete packets called quanta, rather than continuously.
6
State the relationship between the energy of a quantum and the frequency of radiation according to Planck.
Model answer
The energy of each quantum is proportional to the frequency of the radiation, given by E = hf.

See the rest and revise

Other ways to work this

The same content, four other ways.

What is inside Levo

Six ways to work the same material.

1Closed book

2Open book

3Closed book

The 3-step method, run for you

Answer cold, learn it, then prove it stuck. Levo tracks the jump between your first attempt and your last.

Measurements and Their Errors

Particles and Radiation

Waves

Mechanics and Materials

Cram a whole paper in one sitting

Sort every topic into what you know and what you do not, then drill only the weak ones.

Q is .

positivenegativezero

Blank Blitz makes facts automatic

Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

AP = 4πr²σT⁴.

BThe surface area of a spherical star is 4πr².

CP₁/P₂ = (r₁²/r₂²) × (T₁⁴/T₂⁴).

Build It gets the exam shape right

Assemble a full-mark answer from its marking points, in the order an examiner wants them.

Speed means rate of change of distance.

TrueFalse

Test It catches misconceptions

Spot the fault in a statement. The traps are the mistakes students actually make.

721941163128510

Brain Breaks between sessions

Short focus games to reset attention, so the next set lands better than the last.

Every question in Turning Points in Physics, on a schedule.

Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.

Start revising, £5 a month See how the method works

Or £46 a year, about £3.83 a month. Cancel anytime.