Turning Points in Physics | AQA A-Level Physics (7408)
Turning Points in Physics
- 262 questions
- 14 subtopics
- Paper 3 Section B: one option of five
- Paper 3
Turning points in physics is one of the five optional topics, sat on Paper 3.
It follows three arguments that changed the subject: the discovery of the electron, the long dispute over whether light is a wave or a particle, and the experiment that led to special relativity.
Sample questions from Turning Points in Physics
Answer each one closed book first, then open the answer.
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Cathode rays
Where do the electrons in a discharge tube originate from?
Show the answer
Electrons are emitted from the cathode. -
Thermionic emission of electrons
Calculate the electron speed when potential difference = 900 V, electron charge = 1.60 × 10⁻¹⁹ C, electron mass = 9.11 × 10⁻³¹ kg.
Show the answer
Electron speed = √(2 × 1.60 × 10⁻¹⁹ × 900 ÷ (9.11 × 10⁻³¹)) = 1.78 × 10⁷ m s⁻¹. -
Principle of Millikan's determination of the electronic charge, e
As a falling oil droplet speeds up, what happens to the viscous drag force acting on it?
Show the answer
The viscous drag force increases with speed. -
Newton's corpuscular theory of light
Why was the corpuscular theory considered to provide a simpler explanation for observed optical phenomena at the time?
Show the answer
It straightforwardly explained rectilinear propagation and sharp shadows, which wave theory struggled to explain without understanding diffraction. -
Electromagnetic waves
How did Maxwell conclude that light is an electromagnetic wave?
Show the answer
Maxwell calculated the speed of electromagnetic waves using his formula and found it matched the measured speed of light, leading him to predict that light is an electromagnetic wave. -
The discovery of photoelectricity
In the equation λ = h/√(2meV), identify what each symbol represents.
Show the answer
λ is the de Broglie wavelength, h is Planck's constant, m is the electron mass, e is the electron charge, and V is the accelerating potential difference. -
The Michelson-Morley experiment
After recombining at the beam splitter, where do the beams travel?
Show the answer
The recombined beams travel to a detector. -
Einstein's theory of special relativity
Why does special relativity imply there is no absolute or preferred inertial frame?
Show the answer
Because the two postulates together mean that all inertial frames are equivalent for describing physical phenomena, so no single frame can be singled out as special.
The 14 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Cathode rays | Discharge tubes, why low pressure is needed, and how electrons are accelerated. | 14 |
| Thermionic emission of electrons | Releasing electrons from a heated metal, and the work done accelerating them through a potential difference. | 13 |
| Specific charge of the electron | Thomson's experiment, balancing the electric and magnetic fields, and what the result implied. | 25 |
| Principle of Millikan's determination of the electronic charge, e | The oil drop experiment, Stokes' law, terminal speed, and the quantisation of charge. | 22 |
| Newton's corpuscular theory of light | How the corpuscular theory explained reflection and refraction, and where it conflicted with wave theory. | 15 |
| Significance of Young's double slits experiment | Why interference could not be explained by particles, and when wave theory was accepted. | 12 |
| Electromagnetic waves | Maxwell's prediction of the speed of light, and Hertz's and Fizeau's confirmations. | 24 |
| The discovery of photoelectricity | The ultraviolet catastrophe, Planck's quantum, and Einstein's photon explanation. | 28 |
| Electron microscopes | The de Broglie wavelength of an accelerated electron, and the transmission and scanning tunnelling microscopes. | 31 |
| The Michelson-Morley experiment | The apparatus, what an ether would have produced, and what the null result meant. | 20 |
| Einstein's theory of special relativity | Inertial frames, the two postulates, and the consequences of a constant speed of light. | 11 |
| Time dilation | The Lorentz factor, proper time, and the muon evidence. | 20 |
| Length contraction | Proper length, contraction along the direction of motion, and when the effect becomes significant. | 11 |
| Relativistic mass and energy | The relativistic equations for total energy, rest energy and mass, how mass and kinetic energy vary with speed, why a particle with mass never reaches the speed of light, and Bertozzi's direct test of kinetic energy against speed. | 16 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
AQA A-Level Physics Active Recall Guide
Every topic, not just this one. 3,682 questions with their answers.