A-Level · Physics · AQA · Mark scheme decoded
AQA A-Level Physics: Supernovae, Neutron Stars, Black Holes, and Gamma Ray Bursts — mark scheme explained
The short answer
In this section of AQA A-Level Physics, we delve into the defining properties of supernovae, neutron stars, black holes, and gamma ray bursts.
The question
A supernova has an absolute magnitude that increases by 15 magnitudes over a period of 20 days. Calculate the rate of increase in magnitude per day.
[Paraphrased for study — not reproduced from any exam paper.]
Mark scheme, decoded
How the examiner actually awards the marks on this topic.
Gradora's own decode of the marking approach — not the exam board's published mark scheme.
How marks are awarded
For calculation questions, show all steps clearly and include units. For conceptual questions, provide clear and concise explanations, using examples where appropriate. Always check your answers for accuracy and completeness.
What the command words demand
- Define
- Provide a clear and concise definition.
- Explain
- Give reasons or details to clarify a concept.
- Calculate
- Perform a mathematical operation to find a specific value.
- Compare
- Highlight similarities and differences between two or more concepts.
- Describe
- Provide a detailed account of a phenomenon or process.
Model answer
A full-mark response to the question above, worked through step by step.
Timing: Allocate approximately 10-15 minutes to answer questions on this topic, depending on the complexity of the question.
- Identify the total change in magnitude: ΔM = 15 magnitudes0 marks
- Identify the time period over which this change occurs: Δt = 20 days1 mark
- Calculate the rate of increase in magnitude per day: Rate = ΔM / Δt = 15 / 20 = 0.75 magnitudes/day2 marks
Final answer: The rate of increase in magnitude is 0.75 magnitudes per day.
Work through every step correctly and you earn all 3 marks.
Another worked example
A neutron star has a mass of 1.4 solar masses and a radius of 10 km. Calculate its density.
- Convert the mass to kilograms: M = 1.4 × 1.989 × 10 30 kg ≈ 2.785 × 10 30 kg1 mark
- Calculate the volume of the neutron star using the formula for the volume of a sphere: V = (4/3)πr 31 mark
- Substitute r = 10 km = 10,000 m into the volume formula: V ≈ (4/3) × π × (10,000) 3 ≈ 4.19 × 10 12 m 31 mark
- Calculate the density using ρ = M / V: ρ ≈ 2.785 × 10 30 kg / 4.19 × 10 12 m 3 ≈ 6.65 × 10 17 kg/m 31 mark
Final answer: The density of the neutron star is approximately 6.65 × 10 17 kg/m 3 .
Work through every step correctly and you earn all 4 marks.
Common mistakes
Confusing absolute magnitude with apparent magnitude when discussing supernovae.
Why it happens: Students often mix up the terms, leading to incorrect calculations and explanations.
Fix: Always clearly define and distinguish between absolute magnitude (intrinsic brightness) and apparent magnitude (observed brightness).
Forgetting that the density of neutron stars is much higher than that of atomic nuclei.
Why it happens: Students may not fully grasp the extreme conditions in neutron stars, leading to underestimations of their density.
Fix: Emphasize the high density of neutron stars and compare it to familiar objects like atomic nuclei.
Incorrectly stating that light can escape from a black hole's event horizon.
Why it happens: Students may misunderstand the concept of the event horizon, leading to incorrect statements about light escaping.
Fix: Clarify that the escape velocity at the event horizon is greater than the speed of light, making it impossible for anything to escape.
Failing to recognize that gamma ray bursts are caused by the collapse of supergiant stars into neutron stars or black holes.
Why it happens: Students may not fully understand the mechanisms behind gamma ray bursts, leading to incorrect explanations.
Fix: Explain the process of star collapse and the formation of jets of high-energy particles that produce gamma rays.
Misinterpreting the light curve of a type Ia supernova as having a constant brightness.
Why it happens: Students may not understand the shape and characteristics of the light curve, leading to incorrect descriptions.
Fix: Describe the rapid rise to maximum brightness followed by a slower decline in the light curve of a type Ia supernova.
Confusing dark energy with dark matter when discussing the accelerating universe.
Why it happens: Students may mix up these two concepts, leading to incorrect explanations and answers.
Fix: Clearly define and distinguish between dark energy (a form of energy that causes the expansion of the universe to accelerate) and dark matter (a form of matter that does not interact with electromagnetic radiation but affects gravitational interactions).
Forgetting to convert units when calculating the Schwarzschild radius.
Why it happens: Students may overlook unit conversions, leading to incorrect calculations.
Fix: Always check and convert units before substituting values into formulas, especially for mass (solar masses to kilograms) and speed of light (m/s).
Incorrectly stating that supermassive black holes are only found in the centers of large galaxies.
Why it happens: Students may have a limited understanding of where supermassive black holes can be found, leading to incorrect statements.
Fix: Clarify that supermassive black holes are commonly found at the centers of many galaxies, including smaller ones.
Where the marks go
The question types you’ll meet on this topic and the marks each one carries — so you know what to expect and where to focus.
| Question type | What you’re asked to do | Marks |
|---|---|---|
| Calculate Rate | Find the rate of magnitude change by dividing total change by the time period. | 3 |
| Calculate Density | Find a neutron star's density from its mass and radius using volume of a sphere. | 4 |
| Calculate Schwarzschild Radius | Convert the mass to kilograms and apply the Schwarzschild radius formula to find Rs. | 5 |
| Distance Modulus Calculation | Rearrange the distance modulus formula to find a supernova's distance in parsecs. | 5 |
| Total across these question types | 17 | |
Question types and mark tariffs are Gradora’s guidance based on how this topic is typically examined — not the board’s official paper structure.