Free E.5 Fusion & stars questions for IB Physics (SL & HL), part of E Nuclear & quantum physics. Each question has the answer and the marking points an examiner would look for.
Generate a full E.5 Fusion & Stars worksheet →All E Nuclear & quantum physics questionsA main-sequence star much more massive than the Sun reaches the end of its main-sequence life. Which row describes its next stage and final state?
| next stage | final state | |
|---|---|---|
| A | red giant | white dwarf |
| B | red supergiant | white dwarf |
| C | red supergiant | neutron star or black hole |
| D | white dwarf | black hole |
Answer: C
A star of luminosity 7.6 × 1026 W is 9.5 × 1016 m from the Earth.
What is its apparent brightness?
Answer: A
The Sun has luminosity 3.83 × 1026 W and surface temperature 5800 K. Star X has luminosity 40 times that of the Sun and surface temperature 10 000 K.
Calculate the radius of X in terms of the radius of the Sun.
Calculate the peak wavelength of the light from X.
X is 25 pc from Earth (1 pc = 3.09 × 1016 m). Calculate its apparent brightness.
Explain how X remains stable while on the main sequence.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 2.1 R☉ L ∝ R2T4 ✓ RX/R☉ = √40 × (5800/10 000)2 ✓ = 2.1 ✓ | 3 |
| (b) | 290 nm λ = 2.9 × 10−3/10 000 = 2.9 × 10−7 m ✓ | 1 |
| (c) | 2.0 × 10−9 W m−2 b = L/4πd2 ✓ = 2.0 × 10−9 W m−2 ✓ | 2 |
| (d) | pressure balances gravity gravitational pressure acts inwards ✓ balanced by radiation and gas pressure from fusion outwards ✓ | 2 |
This question is about the evolution of stars.
State the main source of energy for a main-sequence star.
Describe the evolution of a star of one solar mass after it leaves the main sequence.
State what is meant by the Chandrasekhar limit.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | hydrogen fusion fusion of hydrogen into helium in the core ✓ | 1 |
| (b) | red giant → PN → white dwarf becomes a red giant ✓ outer layers ejected as a planetary nebula ✓ core becomes a white dwarf ✓ | 3 |
| (c) | 1.4 M☉ the maximum mass of a white dwarf, about 1.4 solar masses ✓ | 1 |
A star has a surface temperature of 4000 K and a luminosity 100 times that of the Sun (Sun: 5800 K).
Calculate the peak wavelength of the star.
Calculate the ratio of the star’s radius to the Sun’s radius.
Identify the type of star.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 725 nm λ = 2.9 × 10−3/4000 = 725 nm ✓ | 1 |
| (b) | 21 L ∝ R2T4 ✓ R/R☉ = 10 × (5800/4000)2 = 21 ✓ | 2 |
| (c) | red giant red giant ✓ | 1 |
A star cluster has a parallax angle of 4.0 × 10−3 arc-seconds. The most luminous stars in the cluster that are still on the main sequence have an apparent brightness of 2.05 × 10−11 W m−2 and a peak emission wavelength of 290 nm. For main-sequence stars, L ∝ M3.5. The Sun’s luminosity is 3.83 × 1026 W and its main-sequence lifetime is 1.0 × 1010 years. 1 pc = 3.09 × 1016 m, Wien constant = 2.9 × 10−3 m K, σ = 5.67 × 10−8 W m−2 K−4.
Determine the luminosity of one of these stars in terms of the Sun’s luminosity.
Estimate the age of the cluster.
A red giant in the cluster has the same apparent brightness as these stars but a peak wavelength of 580 nm. Determine the radius of the red giant.
A student suggests that a white dwarf found in the cluster formed from a star of mass 1.0 solar masses. Explain why this is not possible.
Predict the luminosity of the most luminous main-sequence stars when the cluster is four times its present age.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | ≈ 40 L☉ d = 1/p = 250 pc = 7.7 × 1018 m ✓ L = 4πd2b = 1.5 × 1028 W ✓ L ≈ 40L☉ ✓ | 3 |
| (b) | ≈ 7 × 10⁸ years M = 401/3.5 = 2.9M☉ ✓ lifetime ∝ (fuel)/(rate of use) ∝ M/L ∝ M−2.5 ✓ turn-off stars are just ending their main-sequence life, so cluster age ≈ their lifetime ✓ age ≈ 1.0 × 1010 × 2.87−2.5 ≈ 7 × 108 years ✓ | 4 |
| (c) | 5.9 × 10⁹ m same distance and brightness, so same luminosity ✓ T = 2.9 × 10−3/580 × 10−9 = 5000 K ✓ R = √(L/4πσT4) = 5.9 × 109 m ✓ | 3 |
| (d) | 1 M☉ star still on main sequence a 1.0 M☉ star has a main-sequence lifetime of 1.0 × 1010 years ✓ this exceeds the cluster age, so it cannot yet have left the main sequence; the progenitor must have been more massive than the turn-off mass ✓ | 2 |
| (e) | ≈ 5.7 L☉ age ∝ M−2.5 and L ∝ M3.5, so turn-off L ∝ age−1.4 ✓ L = 40 × 4−1.4 ≈ 5.7L☉ ✓ | 2 |
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Meet Riyaz →Original IB-style practice questions written for mentorriyaz.in. These are not IB past paper questions, and this site is not affiliated with or endorsed by the International Baccalaureate Organization. Updated 2026-11-04. Paper generator · mentorriyaz.in