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
What each mark is really for — in plain English — and the wording trap that loses it.
- S1
Identify the total change in magnitude: ΔM = 15 magnitudes
- S2
Identify the time period over which this change occurs: Δt = 20 days
- S3
Calculate the rate of increase in magnitude per day: Rate = ΔM / Δt = 15 / 20 = 0.75 magnitudes/day
Model answer
Worked through, with each step tagged to the mark it earns.
- S1
Identify the total change in magnitude: ΔM = 15 magnitudes
- S2
Identify the time period over which this change occurs: Δt = 20 days
- S3
Calculate the rate of increase in magnitude per day: Rate = ΔM / Δt = 15 / 20 = 0.75 magnitudes/day
Final answer: The rate of increase in magnitude is 0.75 magnitudes per day.
Common mistakes
- Confusing absolute magnitude with apparent magnitude when discussing supernovae. — 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. — 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. — 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. — 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. — 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. — 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. — 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. — Clarify that supermassive black holes are commonly found at the centers of many galaxies, including smaller ones.
Where the marks go
- Full worked solution (all marking points)3 marks