International GCSE Physics · Pearson Edexcel 4PH1 · Topic 8
Astrophysics
Original exam-style questions with mark schemes. Questions marked “Paper 2 only” use content assessed only on Paper 2. Notes 8(b) →Notes 8(c) →Notes 8(d) →
39questions
215marks
Freefull mark schemes
Original questions in the style of each exam boardEvery answer re-solved independently before publishingCreated by Evan Kotronis with AI assistanceUpdated 13 October 2026 · new questions added regularlyHow every question is checked →
1IGCSE-PHY-8-001Galaxies, stars and the universePapers 1 & 2Grade 4–51 mark
Which statement about the universe is correct?
Show mark scheme
B (the universe contains billions of galaxies and a galaxy contains billions of stars);
A is incorrect because the Milky Way is a galaxy, not a star, and the solar system is inside it
C is incorrect because the order of scale is reversed: galaxies are far larger than the solar system
D is incorrect because the solar system is inside the Milky Way, not the other way round
2IGCSE-PHY-8-002Mass and weight on the MoonPapers 1 & 2Grade 4–51 mark
An astronaut has a mass of 80 kg on the Earth. The gravitational field strength on the Earth is 10 N/kg and on the Moon is 1.6 N/kg. Which row gives the mass and the weight of the astronaut on the Moon?
Show mark scheme
D (mass = 80 kg, weight = 128 N);
A is incorrect because weight depends on g, which is smaller on the Moon (800 N is the weight on Earth)
B is incorrect because it confuses mass with weight; mass is measured in kg and does not change
C is incorrect because mass does not depend on location (80 × 1.6 ÷ 10 = 12.8 ≈ 13 kg wrongly scales the mass)
6IGCSE-PHY-8-008Classifying stars by colourPapers 1 & 2Grade 4–56 marks
The table gives the surface temperature of five stars. Star / name: Rigel, Deneb, Sun, Arcturus, Antares Surface temperature / K: 12100, 8500, 5800, 4300, 3500
(a)
Give the name of the star in the table that appears red.
(1)
(b)
Describe how the colour of a star is related to its surface temperature.
(2)
(c)
The star Vega has a similar colour to Deneb. Suggest a value for the surface temperature of Vega.
(1)
(d)
Near the end of its life, the Sun will become a red giant. Its outer layers will expand and cool. Explain how the colour of the Sun will change.
(2)
Show mark scheme
(a)
Antares;
Do not accept
Arcturus
more than one star given
(b)
hotter stars are blue / white;
cooler stars are red / orange;
Allow
the higher the temperature the bluer the star (for both marks if both ends implied)
correct colour sequence red, orange, yellow, white, blue with increasing temperature for 2 marks
Do not accept
red stars are hottest
colour depends on distance from Earth
(c)
any value from 7500 to 11 000 (K);
Do not accept
value outside the range
value in °C
(d)
(surface) temperature decreases / it gets cooler;
(so) colour changes from yellow (or white) to red / orange;
8IGCSE-PHY-8-022Ordering star colours by surface temperaturePapers 1 & 2Grade 4–51 mark
Stars can be classified according to their colour. Which list gives star colours in order of increasing surface temperature (coolest first)?
Show mark scheme
C (red, orange, yellow, white, blue);
A is incorrect because it is in order of decreasing temperature (hottest first)
B is incorrect because orange stars are cooler than yellow stars
D is incorrect because blue stars are the hottest, not the coolest; the everyday link between blue and cold does not apply to stars
10IGCSE-PHY-8-024Correcting errors in notes on the life cycle of the SunPapers 1 & 2Grade 4–55 marks
A student writes four statements about the life cycle of a star with a mass similar to the Sun. Each statement contains one mistake. 1 The star forms from a nebula, which is pulled together by magnetic forces. 2 During the main sequence stage, nuclear fission of hydrogen releases energy in the core. 3 When the hydrogen in the core runs out, the star shrinks and becomes a red giant. 4 At the end of its life, the star explodes in a supernova, leaving a white dwarf.
(a)
For each statement, identify the mistake and write the correct word or words.
(4)
(b)
Describe what a white dwarf is.
(1)
Show mark scheme
(a)
statement 1: gravitational force / gravity (not magnetic);
statement 2: fusion (not fission);
statement 3: expands / gets bigger (not shrinks);
statement 4: no supernova / outer layers are released (drift away) / star sheds its outer layers;
Allow
statement 4: 'only massive stars explode as a supernova' or 'the star does not explode'
Do not accept
statement 4: 'it becomes a neutron star' / 'black hole'
statement 2: 'chemical burning'
(b)
(small) hot dense core (remnant) of the star;
Allow
small hot star that no longer has fusion / cools down over time
11IGCSE-PHY-8-026Classifying the two stars of Albireo by colourPapers 1 & 2Grade 4–56 marks
Albireo looks like a single star to the naked eye. Through a telescope it is seen to be two stars close together in the sky. Albireo A is orange and Albireo B is blue. Astronomers use letters to classify stars according to their colour. Class / letter: O, B, A, F, G, K, M Colour / name: blue, blue-white, white, yellow-white, yellow, orange, red
(a)
The Sun is a yellow star. State the class of the Sun.
(1)
(b)
State which of the two stars of Albireo has the higher surface temperature. Give a reason for your answer.
(2)
(c)
Describe how the surface temperature of a star changes from class O to class M.
(1)
(d)
A student says: 'Albireo A and Albireo B have different colours, so they must be at different distances from the Earth.' Explain why the colours of the two stars do not give any information about their distances from the Earth.
(2)
Show mark scheme
(a)
G;
Do not accept
yellow (colour not class)
(b)
Albireo B;
blue stars are hotter (than orange stars) / orange stars are cooler;
Allow
MP2 can be scored by a correct comparison of colour order (e.g. blue is at the hot end)
B with no reason scores 1
Do not accept
Albireo A
blue means colder
(c)
temperature decreases (from O to M);
Allow
O hottest and M coolest
Do not accept
increases
(d)
colour (of a star) depends on (is related to) its surface temperature;
colour does not depend on distance / distance affects brightness (how bright it appears) not colour;
Allow
a star further away appears dimmer but the same colour, for MP2
Do not accept
colour depends on the size of the star
stars further away look redder (as the only point)
12IGCSE-PHY-8-006Speed of a geostationary satellitePapers 1 & 2Grade 6–71 mark
A communications satellite orbits the Earth once every 24.0 hours. The orbital radius of the satellite is 42 200 km. What is the orbital speed of the satellite?
Show mark scheme
A (3070 m/s);
B is incorrect because it omits 2π (distance taken as the radius, 4.22 × 10⁷ ÷ 86 400)
C is incorrect because the radius was left in km while the time was in seconds
D is incorrect because the time was left in hours instead of being converted to seconds
13IGCSE-PHY-8-007Orbital period of the International Space StationPapers 1 & 2Grade 6–76 marks
The International Space Station (ISS) is an artificial satellite in a circular orbit around the Earth. The orbital radius of the ISS, measured from the centre of the Earth, is 6780 km. The orbital speed of the ISS is 7.66 km/s.
(a)
State the name of the force that keeps the ISS in orbit and the direction in which this force acts on the ISS.
(2)
(b)
Calculate the time period of the orbit of the ISS. Give your answer in minutes.
14IGCSE-PHY-8-009Data analysis: gravitational field strength of planetsPapers 1 & 2Grade 6–76 marks
The table gives data for some bodies in the solar system. Mass and radius are given as multiples of the values for the Earth. Body / name: Mercury, Venus, Earth, Moon, Mars, Jupiter Mass / Earth masses: 0.055, 0.815, 1.00, 0.012, 0.107, 318 Radius / Earth radii: 0.383, 0.949, 1.00, 0.273, 0.532, 11.2 Surface gravitational field strength / N/kg: 3.7, 8.9, 9.8, 1.6, 3.7, 24.8
(a)
Give the names of the two bodies in the table that have the same surface gravitational field strength.
(1)
(b)
Jupiter has 318 times the mass of the Earth, but its surface gravitational field strength is only about 2.5 times that of the Earth. Use the data to suggest why.
(2)
(c)
A student says: 'The greater the mass of a planet, the greater the gravitational field strength at its surface.' Evaluate this statement using the data in the table.
(3)
Show mark scheme
(a)
Mercury and Mars;
Do not accept
only one named
(b)
Jupiter has a (much) larger radius / is much bigger;
(so) surface is further from the centre (of the planet), reducing g;
Allow
radius 11.2 times Earth's quoted for MP1
g also depends on radius / size for MP2
Do not accept
Jupiter is a gas so has less gravity
Jupiter is further from the Sun
(c)
any three from:
trend supported for most bodies, e.g. Moon has smallest mass and smallest g / Jupiter largest mass and largest g;
Mars has (about twice) more mass than Mercury but the same g;
(because) Mars has a larger radius (than Mercury);
conclusion: g depends on radius as well as mass, so statement is not always true;
Allow
comparison of Venus and Earth (mass ratio 0.815, g ratio 0.91) as a valid trend example
Do not accept
unsupported 'the student is right/wrong' with no data
16IGCSE-PHY-8-011Practical: determining g on the Moon from a light-gate dropPapers 1 & 2Grade 6–79 marks
Astronauts on the Moon test a light gate. A small steel ball is released from rest and falls a measured distance s through the light gate. The light gate measures the speed v of the ball. The astronauts repeat this for different distances s. The graph shows v² plotted against s, with a line of best fit. There is no atmosphere on the Moon.
(a)
State the equation linking final speed, initial speed, acceleration and distance moved.
(1)
(b)
Explain why the graph of v² against s is a straight line through the origin.
(2)
(c)
Use the graph to determine the acceleration of the ball on the Moon.
(4)
(d)
A scientific instrument has a mass of 4.5 kg. Use your answer to (c) to calculate how much less the instrument weighs on the Moon than on the Earth. (g on Earth = 10 N/kg)
17IGCSE-PHY-8-025Comparing the orbital speeds of two satellitesPapers 1 & 2Grade 6–71 mark
Satellites X and Y are in circular orbits around the Earth. The orbital radius of Y is 4 times the orbital radius of X. The time period of Y is 8 times the time period of X. How does the orbital speed of Y compare with the orbital speed of X?
Show mark scheme
D (half the speed of X);
A is incorrect: this comes from dividing the period ratio by the radius ratio (8 ÷ 4) instead of radius ratio ÷ period ratio
B is incorrect: this uses only the radius ratio and ignores the longer time period
C is incorrect: this uses only the period ratio (1 ÷ 8) and ignores the larger radius
18IGCSE-PHY-8-027Data: how g varies with distance from the EarthPapers 1 & 2Grade 6–76 marks
The graph shows how the gravitational field strength, g, varies with distance from the centre of the Earth. The dashed line shows the Earth's surface.
(a)
Describe how g changes as the distance from the centre of the Earth increases.
(2)
(b(i))
A weather satellite orbits at a height of 3600 km above the Earth's surface. Use the graph to determine the gravitational field strength at the satellite.
(1)
(b(ii))
The mass of the satellite is 1500 kg. Calculate the gravitational force (weight) acting on the satellite in orbit.
(2)
(c)
State the effect of this gravitational force on the motion of the satellite.
(1)
Show mark scheme
(a)
(g) decreases (as distance increases);
rate of decrease gets less / curve not straight / not (inversely) proportional to distance / doubling distance gives about a quarter of g;
Allow
falls quickly near the Earth and more slowly further away, for MP2
Do not accept
g decreases linearly
g becomes zero
(b(i))
(read at 10 000 km) 4.0 (N/kg);
Allow
3.9–4.1 (N/kg)
Do not accept
a value read at 3.6 (thousand km) on the axis (height used instead of distance from centre)
9.8 (surface value)
(b(ii))
substitution;
evaluation;
e.g. W = 1500 × 4.0
(W =) 6000 (N)
Allow
ECF from b(i)
5850–6150 (N) from a reading in the range 3.9–4.1
14 700 (N) (using 9.8 N/kg) scores 1 for substitution of a value of g
Do not accept
6.0 (N) (POT error with mass in tonnes) for evaluation
(c)
keeps it in orbit (around the Earth) / makes it move in a circle (rather than a straight line);
19IGCSE-PHY-8-028Practical: weight against mass with a newtonmeterPapers 1 & 2Grade 6–78 marks
A student investigates the relationship between the weight and the mass of objects in the laboratory. The student hangs slotted masses on a newtonmeter, as shown in the diagram, and records the reading for each mass. Mass / kg: 0.10, 0.20, 0.30, 0.40, 0.50, 0.60 Weight / N: 1.0, 2.0, 2.9, 3.9, 4.9, 5.9
(a)
Give two things the student should do to make sure each newtonmeter reading is accurate.
(2)
(b)
The student plots a graph of weight (y-axis) against mass (x-axis). The graph is a straight line through the origin. State what the gradient of this graph represents and give its unit.
(2)
(c)
Use the data in the table to determine a value for the gravitational field strength in the laboratory.
(2)
(d)
The unit of gravitational field strength can also be written as m/s². Use the relationship force = mass × acceleration to show that 1 N/kg is the same as 1 m/s².
(2)
Show mark scheme
(a)
any two from:
check newtonmeter reads zero before adding masses / zero the newtonmeter;
read scale at eye level / perpendicular to the scale;
wait for masses to stop moving (oscillating) before reading;
newtonmeter vertical / not touching the stand;
Allow
use a newtonmeter with a smaller scale division (higher resolution)
Do not accept
repeat readings (alone, improves reliability not accuracy of a single reading)
use a balance
(b)
(gravitational) field strength / g;
N/kg;
Allow
m/s² for MP2
weight per unit mass for MP1
Do not accept
gravity for MP1
N for MP2
acceleration (alone) for MP1
(c)
substitution into g = W ÷ m (any pair of values) or gradient calculation;
evaluation;
e.g. g = 5.9 ÷ 0.60
(g =) 9.8 (N/kg)
Allow
9.67–10 (N/kg) from any pair of data or a gradient
10 (N/kg) from 1.0 ÷ 0.10 or 2.0 ÷ 0.20
Do not accept
10 N/kg quoted from memory with no working (scores 0)
(d)
1 N = 1 kg × 1 m/s² (from F = m × a);
so N/kg = (kg × m/s²) ÷ kg = m/s²;
Allow
argument using units only: N = kg m/s², N/kg = kg m/s² ÷ kg
20IGCSE-PHY-8-029Speed of a lunar orbiterPapers 1 & 2Grade 6–76 marks
A spacecraft called an orbiter moves in a circular orbit around the Moon. The orbiter is 100 km above the Moon's surface. The radius of the Moon is 1740 km. The time period of the orbit is 118 minutes.
(a)
Calculate the orbital speed of the orbiter. Give your answer in m/s.
(4)
(b)
A satellite in a low orbit around the Earth has an orbital speed of about 7800 m/s. Suggest why the orbital speed of the orbiter around the Moon is much smaller.
(2)
Show mark scheme
(a)
orbital radius = 1840 km / 1.84 × 10⁶ m;
T = 7080 s;
substitution into v = 2πr/T;
evaluation;
e.g. v = 2 × π × 1.84 × 10⁶ ÷ 7080
(v =) 1630 (m/s)
Allow
1633 (m/s), 1600 (m/s)
1540 (m/s) (using r = 1740 km) scores 3
1.63 (m/s) or 1630 km/s POT error scores 3
98 000 (using T in minutes and r in m) scores 3
Do not accept
89 (m/s) (using 100 km as radius) for MP1
(b)
Moon has a (much) smaller mass (than the Earth);
(so) gravitational force on the orbiter / gravitational field strength (at the orbit) is weaker;
Allow
Moon's gravitational field is weaker for MP2
(so) a smaller speed is enough for gravity to keep it in orbit, as an alternative to MP2 if linked to weaker gravity
21IGCSE-PHY-8-030The Crab Nebula: evidence from a supernova remnantPapers 1 & 2Grade 6–76 marks
In the year 1054, astronomers in China recorded a 'guest star' that suddenly appeared in the sky. It was bright enough to be seen in daylight for several weeks and then slowly faded. Today, telescopes pointed at the same position show the Crab Nebula: an expanding cloud of gas and dust with a neutron star at its centre.
(a)
Name the event that the astronomers saw in 1054.
(1)
(b)
Astronomers know that the star that produced the Crab Nebula had a much greater mass than the Sun. Explain how the information above shows this.
(2)
(c)
Before this event, the core of the star collapsed. Explain why the core collapsed.
(2)
(d)
A neutron star is one type of object that can be left after this event. Name the other type of object that can be left.
(1)
Show mark scheme
(a)
supernova;
Do not accept
nova
red giant / red supergiant
white dwarf
(b)
it exploded as a supernova / it left a neutron star (at the centre);
stars with a mass similar to the Sun do not explode / end as a white dwarf (after losing their outer layers gently);
Allow
only stars much more massive than the Sun become supernovae / neutron stars, for MP2
Do not accept
it was very bright so it was very big (with no reference to supernova or remnant)
the Sun will become a neutron star
(c)
(nuclear) fusion (in the core) stopped / fuel for fusion ran out / no more outward pressure (from energy released);
inward gravitational force no longer balanced / gravity pulled the core inwards;
Allow
the outward force no longer balanced the inward force of gravity scores 2
Do not accept
fission for fusion
the star ran out of oxygen / stopped burning (chemical)
22IGCSE-PHY-8-012Evaluating a claim about planetary orbital speedsPapers 1 & 2Grade 8–98 marks
The table gives data about the orbits of four planets around the Sun. Planet / name: Mercury, Earth, Mars, Jupiter Orbital radius / 10⁹ m: 57.9, 150, 228, 778 Time period / days: 88.0, 365, 687, 4330 A student makes this claim: 'Planets further from the Sun must travel faster, because they have a longer distance to travel in each orbit.'
(a)
Calculate the orbital speed of Mercury. Give your answer in km/s.
(3)
(b)
Evaluate the student's claim. Use calculations based on the data in the table to support your answer.
(3)
(c)
Suggest why the orbital speed of a planet depends on its distance from the Sun.
(2)
Show mark scheme
(a)
conversion of time to seconds;
substitution;
evaluation in km/s;
e.g. T = 88.0 × 24 × 3600 = 7 603 200 (s)
v = 2 × π × 57.9 × 10⁹ ÷ 7 603 200
(v =) 47.8 (km/s)
Allow
47.85, 48 (km/s)
47 800 m/s scores 2
ECF from incorrect time conversion
Do not accept
v = 2πrT
(b)
any three from:
orbital speed of at least one other planet correctly calculated (Earth 29.9 / Mars 24.1 / Jupiter 13.1 km/s);
statement that further planets have lower orbital speeds;
idea that time period increases by a greater factor than orbital radius / circumference (e.g. Jupiter radius ×13.4 but period ×49);
conclusion that the claim is incorrect;
Allow
ECF from (a)
speeds in m/s
Do not accept
unsupported conclusion with no calculation or comparison
(c)
gravitational force (of Sun) is weaker further from the Sun;
(so) a lower speed is needed to stay in orbit / planet is accelerated less;
23IGCSE-PHY-8-013Life cycle of a massive starPapers 1 & 2Grade 8–96 marks
A star forms with a mass about 20 times the mass of the Sun.
(a)
Describe and explain the life cycle of this star, from its formation to its final stage. You should refer to the roles of gravity and nuclear fusion in your answer.
(6)
Show mark scheme
(a)
Indicative content:
MP1. star forms from a nebula / cloud of gas and dust;
MP2. gravity pulls the gas and dust together / nebula collapses and heats up;
MP3. (hydrogen) fusion starts in the core → main-sequence star;
MP4. star is stable because (outward) force/pressure from fusion energy balances (inward) gravity;
MP5. massive star uses up its hydrogen faster / spends less time on main sequence (than the Sun);
MP6. when hydrogen in the core runs out, the star expands to become a red supergiant;
MP7. fusion of heavier elements in the core;
MP8. fusion stops and gravity causes the core to collapse;
MP9. supernova explosion;
MP10. leaves a neutron star;
MP11. or a black hole if the remaining core is massive enough (gravity so strong light cannot escape);
MP12. material thrown out forms new nebulae;
Allow
award 1 mark per MP to a maximum of 6, but use levels to judge overall quality
red giant for red supergiant
max 4 marks if no reference to gravity or fusion
Do not accept
white dwarf as final stage of this star
fission for fusion
star 'burns' fuel (chemical combustion)
Level 0 (0)
No rewardable content.
Level 1 (1–2)
Names some stages, possibly out of order, with little or no explanation; may include incorrect final stage.
Level 2 (3–4)
Stages mostly in correct order including supernova; some explanation of the role of gravity or fusion at one or two stages.
Level 3 (5–6)
Complete correct sequence nebula → main sequence → red supergiant → supernova → neutron star / black hole, with linked explanations of the role of gravity and fusion at several stages.
24IGCSE-PHY-8-031GPS satellite: orbits per dayPapers 1 & 2Grade 8–96 marks
Satellites in the Global Positioning System (GPS) orbit the Earth in circular orbits. A GPS satellite orbits at a height of 20 200 km above the Earth's surface. The radius of the Earth is 6370 km. The orbital speed of the satellite is 3870 m/s.
(a)
Determine the number of times the satellite orbits the Earth in one day.
(4)
(b)
A student says: 'GPS satellites always stay above the same point on the Earth's surface, because the Earth spins at the same rate as they orbit.' Use your answer to (a) to evaluate the student's statement.
(2)
Show mark scheme
(a)
orbital radius = 26 570 km / 2.657 × 10⁷ m;
rearrangement and substitution into T = 2πr ÷ v;
T = 43 100 s / 12.0 hours;
(number of orbits =) 2.0;
e.g. T = 2 × π × 2.657 × 10⁷ ÷ 3870 = 43 138 s
86 400 ÷ 43 138 = 2.00
Allow
43 000–43 200 (s), 2 / 2.00 / 'twice'
ECF for MP3 and MP4 from an incorrect radius: r = 20 200 km gives T = 32 800 s and 2.6 orbits (scores 3)
alternative route: distance travelled in a day = 3870 × 86 400 = 3.34 × 10⁸ m, divided by 2πr (1.67 × 10⁸ m) = 2.0, for MP2–MP4
Do not accept
answer given as a time with no number of orbits for MP4
T = 2πv ÷ r
(b)
Earth rotates once (per day) while satellite completes two orbits / satellite has a shorter period than the Earth's rotation (24 h);
so it does not stay above the same point / the student is wrong;
25IGCSE-PHY-8-032Data: period and orbital radius of an exoplanet from a light curvePapers 1 & 2Grade 8–98 marks
Astronomers measure the brightness of a distant star over 20 days. A planet orbits this star in a circular orbit. Each time the planet passes between the star and the Earth, the brightness of the star decreases slightly. The graph shows the results.
(a)
State the force that causes the planet to orbit the star.
(1)
(b)
Use the graph to determine the time period of the orbit of the planet. Explain how you used the graph to make your value as accurate as possible.
(3)
(c)
The orbital speed of the planet is 95 km/s. The orbital radius of the planet Mercury around the Sun is 5.8 × 10¹⁰ m. A student says that the planet is much closer to its star than Mercury is to the Sun. Evaluate the student's statement. Use a calculation in your answer.
(4)
Show mark scheme
(a)
gravity / gravitational (force of the star);
Do not accept
magnetic force
centrifugal force
(b)
time between consecutive dips (centres) read from the graph;
(T =) 5.5 days;
measured over several dips (first to last) and divided by number of orbits (3);
Allow
5.4–5.6 (days)
MP1 for e.g. 7.5 − 2.0 = 5.5
Do not accept
11 days (time for two dips counted as one orbit)
width of one dip
(c)
conversion of T to seconds (475 200 s);
substitution into r = vT ÷ 2π (with v in m/s);
evaluation of r;
comparison with Mercury and conclusion (student correct);
e.g. r = 95 000 × 475 200 ÷ (2 × π)
(r =) 7.2 × 10⁹ (m)
7.2 × 10⁹ m is (about 8 times) less than 5.8 × 10¹⁰ m so student is correct
26IGCSE-PHY-8-033Comparing the orbits of four objectsPapers 1 & 2Grade 8–96 marks
The table gives information about four objects that move in orbits. Object / name: Titan, Neptune, Comet Hale–Bopp, Hubble Space Telescope Type of object / type: moon, planet, comet, artificial satellite Shape of orbit / description: almost circular, almost circular, very elliptical, almost circular Time period / approximate: 16 days, 165 years, 2500 years, 95 minutes
(a)
Use the information in the table and your own knowledge to compare the orbits of these four objects. In your answer you should explain the role of gravity.
(6)
Show mark scheme
(a)
Indicative content:
MP1. gravitational force keeps each object in orbit / provides the force towards the body it orbits;
MP2. moon (Titan) orbits a planet / Saturn;
MP3. planet (Neptune) and comet both orbit the Sun;
MP4. artificial satellite (Hubble) orbits the Earth;
MP5. moon, planet and satellite have (almost) circular orbits so distance (and speed) stays (nearly) constant;
MP6. comet's orbit is very elliptical so its distance from the Sun changes a lot;
MP7. comet moves fastest when closest to the Sun because the gravitational force is strongest there;
MP8. comet moves slowly far from the Sun / spends most of its time far from the Sun;
MP9. for objects orbiting the Sun, a larger orbit means a longer time period (Neptune 165 years, the comet, which travels much further from the Sun, 2500 years);
MP10. comet's orbit may cross the orbits of planets / comet is not in the same plane (tilted orbit);
Allow
award 1 mark per MP to a maximum of 6, but use levels to judge overall quality
Saturn need not be named for MP2
max 4 marks if there is no reference to gravity
Do not accept
centrifugal force balances gravity
comet orbits the Earth
speed of comet constant
Level 0 (0)
No rewardable content.
Level 1 (1–2)
Isolated statements about one or two objects, e.g. what they orbit or orbit shape, with little or no comparison or reference to gravity.
Level 2 (3–4)
Some comparison of what the objects orbit and the shapes of their orbits; some reference to gravity or to changes in speed or period, but links are incomplete.
Level 3 (5–6)
Coherent comparison covering what each object orbits, orbit shapes and time periods, with linked explanation of the role of gravity including the changing speed of the comet.
27IGCSE-PHY-8-014Doppler effect for a receding galaxyPaper 2 onlyGrade 4–51 mark
A galaxy is moving away from the Earth. Light from the galaxy is compared with light from the same element in a laboratory on Earth. Which row describes the light observed from the galaxy?
Show mark scheme
C (wavelength longer, frequency lower);
A is incorrect because this happens when the source moves towards the observer (blue-shift)
B is incorrect because wavelength and frequency cannot both increase when the speed of light is unchanged (v = f × λ)
D is incorrect because a change in frequency must be accompanied by a change in wavelength
29IGCSE-PHY-8-035Doppler effect: a passing train horn and an orbiting starPaper 2 onlyGrade 4–56 marks
A train travels at a constant speed along a straight track and passes through a station without stopping. The driver sounds the train's horn, which emits sound with a frequency of 400 Hz. A passenger stands still on the platform.
(a)
Describe how the frequency of the sound heard by the passenger compares with 400 Hz • as the train approaches the station • as the train moves away from the station.
(2)
(b)
The speed of sound in air is 340 m/s. Calculate the wavelength of the sound emitted by the horn.
(2)
(c)
Some stars orbit another star. As one of these stars moves around its orbit, it moves towards the Earth for part of the time and away from the Earth for the rest of the time. Describe how the observed wavelength of a line in the spectrum of this star changes as it moves around its orbit.
(2)
Show mark scheme
(a)
higher (than 400 Hz) as the train approaches;
lower (than 400 Hz) as the train moves away;
Allow
higher / lower pitch
'higher then lower' with no reference to 400 Hz scores 1
Do not accept
louder / quieter (loudness is not frequency)
stays at 400 Hz
lower as it approaches and higher as it moves away (scores 0)
(b)
substitution;
evaluation;
e.g. λ = 340 ÷ 400
(λ =) 0.85 (m)
Allow
85 cm
rearrangement of v = f × λ seen for MP1
Do not accept
136 000 (m) (340 × 400) for evaluation
1.18 (m) (400 ÷ 340) for evaluation
(c)
(observed) wavelength is shorter (than the reference wavelength) when the star moves towards the Earth;
(observed) wavelength is longer when the star moves away from the Earth;
Allow
blue-shift for MP1 and red-shift for MP2
wavelength alternately increases and decreases / changes periodically, with no link to direction of motion, scores 1
Do not accept
longer when moving towards the Earth
the star changes colour because its temperature changes
30IGCSE-PHY-8-016Blue-shift of light from the Andromeda galaxyPaper 2 onlyGrade 6–76 marks
The Andromeda galaxy is moving towards the Milky Way. The velocity of Andromeda towards the Earth is 3.0 × 10⁵ m/s. A line in the spectrum of sodium has a reference wavelength of 589.0 nm when measured in a laboratory. The speed of light is 3.0 × 10⁸ m/s.
(a)
Explain whether the wavelength of this sodium line observed in light from Andromeda is longer or shorter than 589.0 nm.
(2)
(b)
Calculate the observed wavelength of this sodium line in light from Andromeda. Give your answer to 4 significant figures.
(3)
(c)
State how the frequency of this line observed in light from Andromeda compares with the frequency measured in the laboratory.
(1)
Show mark scheme
(a)
(observed wavelength is) shorter;
(because) galaxy / source is moving towards the observer / Earth;
Allow
blue-shift for MP1
waves are squashed / compressed for MP2 if linked to motion towards
Do not accept
longer / red-shift (scores 0)
shorter because the galaxy is closer (for MP2)
(b)
rearrangement / substitution;
evaluation of change in wavelength;
subtraction from reference wavelength;
e.g. Δλ = 589.0 × 3.0 × 10⁵ ÷ 3.0 × 10⁸
Δλ = 0.589 (nm)
(λ =) 588.4 (nm)
Allow
588.41 (nm)
589.6 (nm) from adding Δλ scores 2
Do not accept
589.0 (nm) / no change (scores max 1 for the rearrangement)
32IGCSE-PHY-8-019Tracking the Sun's evolution on an HR diagramPaper 2 onlyGrade 6–76 marks
The HR diagram shows the main sequence and the present position of the Sun, S.
(a)
The Sun will become a red giant. Its surface temperature will decrease and its absolute magnitude will decrease (it will be about 1000 times brighter at the standard distance). Explain how the position of the Sun on the HR diagram will change.
(3)
(b)
The Sun will then become a white dwarf. The white dwarf will have a higher surface temperature than the Sun has now but will be about 1000 times less bright at the standard distance. Describe and explain the position of the white dwarf on the HR diagram compared with S and with the main sequence.
(3)
Show mark scheme
(a)
(lower temperature so) moves to the right;
(brighter so) moves up / absolute magnitude decreases (becomes more negative);
ends above the main sequence / in the upper right (red giant region);
33IGCSE-PHY-8-036Doppler shift of radio signals from a deep-space probePaper 2 onlyGrade 6–76 marks
A space probe is travelling directly away from the Earth at a speed of 14.0 km/s. It sends radio signals to the Earth with a frequency of 8.40 GHz. The speed of radio waves is 3.0 × 10⁸ m/s. The equation used for the red-shift of light from galaxies also applies to the radio waves from the probe.
(a)
Calculate the wavelength of the radio waves emitted by the probe.
(2)
(b)
Calculate the change in wavelength of the radio waves received on the Earth.
(3)
(c)
State how the frequency of the radio waves received on the Earth compares with 8.40 GHz.
(1)
Show mark scheme
(a)
substitution;
evaluation;
e.g. λ = 3.0 × 10⁸ ÷ 8.40 × 10⁹
(λ =) 0.0357 (m)
Allow
0.036 (m), 3.57 × 10⁻² (m), 3.6 cm
Do not accept
35.7 (m) (GHz taken as MHz) for evaluation
(b)
rearrangement / Δλ = λ0 × v ÷ c;
substitution with v in m/s;
evaluation;
e.g. Δλ = 0.0357 × 14 000 ÷ 3.0 × 10⁸
(Δλ =) 1.67 × 10⁻⁶ (m)
Allow
ECF from (a)
1.7 × 10⁻⁶ (m)
1.67 × 10⁻⁹ (m) (v left in km/s) scores 2
Do not accept
0.0357 + 1.67 × 10⁻⁶ given as the change in wavelength
34IGCSE-PHY-8-037Data: classifying stars from temperature and absolute magnitudePaper 2 onlyGrade 6–77 marks
The table gives the surface temperature and the absolute magnitude of four stars, P, Q, R and S. Star / letter: P, Q, R, S Surface temperature / K: 4000, 20000, 5800, 9500 Absolute magnitude / no unit: −2, −4, +4.8, +12
(a)
Seen from the Earth, star Q appears much less bright than star R. Suggest how this is possible even though star Q has the more negative absolute magnitude.
(2)
(b)
One of the stars is a white dwarf. Identify this star and explain how the data show that it is a white dwarf.
(3)
(c)
State the group of stars on the HR diagram to which star P belongs and give the colour of star P.
(2)
Show mark scheme
(a)
Q is (much) further away from the Earth (than R);
absolute magnitude is the brightness at a standard distance / how bright a star appears (from Earth) also depends on its distance;
Allow
Q gives out more light but it spreads out over a greater distance, for MP2
Do not accept
Q is cooler (it is hotter)
absolute magnitude of Q is larger so it is dimmer
(b)
S;
high (surface) temperature / hot / white;
large positive absolute magnitude / very dim (at standard distance) / below the main sequence;
35IGCSE-PHY-8-038Practical: balloon model of the expanding universePaper 2 onlyGrade 6–710 marks
A student uses a balloon to model the expansion of the universe. The student draws five ink dots, A to E, on a partly inflated balloon. The dots represent galaxies. The student measures the distance of each dot from dot A along the surface of the balloon. The student then inflates the balloon further and measures the distances again. Dot / name: B, C, D, E Distance from A before / cm: 2.0, 3.5, 5.0, 6.5 Distance from A after / cm: 3.0, 5.3, 7.4, 9.8
(a)
Describe how the student could measure the distance between two dots along the curved surface of the balloon.
(2)
(b)
Use the data to show that the increase in distance of each dot from A is approximately proportional to its original distance from A.
(3)
(c)
Explain how the results of this model are linked to the red-shift of light from galaxies at different distances from the Earth.
(2)
(d)
Another student says: 'All the dots moved away from dot A, so dot A must be at the centre of the expansion. This means the Earth is at the centre of the universe.' Evaluate this statement.
(2)
(e)
State what this model suggests about the universe in the past.
(1)
Show mark scheme
(a)
use string / flexible tape measure along the surface (between the dots);
then measure the string (marked length) with a ruler;
Allow
use a tape measure that bends to fit the surface scores 2
Do not accept
ruler held straight across between dots (ignores curve)
(b)
calculates increases: 1.0, 1.8, 2.4, 3.3 (cm);
calculates increase ÷ original distance (or after ÷ before) for at least three dots;
ratio is (approximately) constant ≈ 0.5 (or 1.5) so proportional;
Allow
ratios 0.48–0.51 or 1.48–1.51
comparison using doubling e.g. D is 2.5 × B's distance and its increase is 2.4 × B's increase, for MP2 and MP3
Do not accept
'the increases get bigger' alone for MP3
(c)
more distant galaxies move away faster (greater recession velocity);
so (light from) more distant galaxies has a greater red-shift;
Allow
more distant dots moved further in the same time, linked to galaxies, for MP1
Do not accept
galaxies further away have a smaller red-shift
red-shift due to galaxies being hotter
(d)
(an observer on) any dot would see all other dots moving away (with the same pattern);
so there is no centre (on the surface) / A is not special, so the statement is wrong;
Allow
the expansion is of space itself, everywhere at once, for MP1
Do not accept
agreeing with the statement
(e)
galaxies were closer together / universe was smaller (and denser, hotter);
36IGCSE-PHY-8-018Data analysis: red-shift, distance and the age of the universePaper 2 onlyGrade 8–910 marks
Astronomers measure the wavelength of a hydrogen line in the light from three galaxies, P, Q and R. The reference wavelength of this line is 486.1 nm. The speed of light is 3.0 × 10⁸ m/s. Galaxy / name: P, Q, R Distance from Earth / 10²⁴ m: 1.5, 3.0, 4.5 Observed wavelength / nm: 491.6, 497.1, 502.6 Recession velocity / 10⁶ m/s: 3.4, 6.8, not given
(a)
Calculate the recession velocity of galaxy R.
(3)
(b)
Use the data to show that the recession velocity of a galaxy is directly proportional to its distance from the Earth.
(2)
(c)
Explain why this relationship provides evidence that the universe is expanding.
(2)
(d)
Assume galaxy R has always moved away from the Earth at its present velocity. Estimate the time, in years, since galaxy R and the Milky Way were at the same place. (1 year = 3.2 × 10⁷ s)
(3)
Show mark scheme
(a)
change in wavelength calculated;
substitution / rearrangement;
evaluation;
e.g. Δλ = 502.6 − 486.1 = 16.5 (nm)
v = 16.5 × 3.0 × 10⁸ ÷ 486.1
(v =) 1.0 × 10⁷ (m/s)
Allow
1.02 × 10⁷, 1.018 × 10⁷, 10 183 090 (m/s)
9.8 × 10⁶ m/s from using 502.6 as denominator scores 2
Do not accept
3.1 × 10⁸ m/s (ratio of wavelengths × c)
(b)
v ÷ d calculated for at least two galaxies;
values the same / constant (≈ 2.3 × 10⁻¹⁸), so v ∝ d;
Allow
distance doubles (P to Q) and velocity doubles; distance ×3 (P to R) and velocity ×3
ECF from (a)
Do not accept
'velocity increases as distance increases' alone (not proportional) for MP2
(c)
(all) galaxies are moving away (from us / red-shifted);
more distant galaxies move faster so galaxies are moving apart from each other / space is expanding;
Allow
red-shift increases with distance for MP1
Do not accept
galaxies are expanding
the Milky Way is at the centre of the universe
(d)
use of time = distance ÷ speed;
evaluation in seconds;
conversion to years;
e.g. t = 4.5 × 10²⁴ ÷ 1.02 × 10⁷
(t =) 4.4 × 10¹⁷ (s)
(t =) 1.4 × 10¹⁰ (years)
Allow
1.38 × 10¹⁰, 1.41 × 10¹⁰, 14 billion (years)
ECF from (a)
use of 3.15 × 10⁷ s per year (1.40 × 10¹⁰ years)
use of data for P or Q (same time, 1.4 × 10¹⁰ years, because v ∝ d)
37IGCSE-PHY-8-020Red-shift of two spectral lines: proportional shiftPaper 2 onlyGrade 8–98 marks
The diagram shows two absorption lines measured in a laboratory, and the same two lines in the spectrum of light from galaxy G. One line is from calcium and the other is from sodium. Laboratory wavelengths: 393.4 nm (calcium) and 589.0 nm (sodium) Wavelengths in light from galaxy G: 409.1 nm (calcium) and 612.6 nm (sodium)
(a)
Explain how the diagram shows that galaxy G is moving away from the Earth.
(2)
(b)
A student says: 'The galaxy has only one velocity, so both lines should be shifted by the same number of nanometres.' Use the data to show that the student is wrong, and explain why the two lines are shifted by different amounts.
(4)
(c)
A line of magnesium has a laboratory wavelength of 517.3 nm. Determine the wavelength of this line in the light from galaxy G.
(2)
Show mark scheme
(a)
lines (in light from G) are at longer wavelengths / shifted towards the red end;
(red-shift) occurs when the source moves away from the observer;
Allow
frequency of the lines is lower for MP1
Do not accept
the galaxy is red
lines shifted to shorter wavelengths
(b)
both changes in wavelength calculated (15.7 nm and 23.6 nm), showing they are different;
Δλ/λ0 calculated for both lines (0.0399 and 0.0401);
Δλ/λ0 is the same (≈ 0.040) for both lines / both give the same velocity;
(because) Δλ/λ0 = v/c, so Δλ is proportional to λ0 / longer reference wavelength gives a bigger shift;
Allow
velocities from both lines (1.20 × 10⁷ m/s and 1.197 × 10⁷ m/s, using c = 3.0 × 10⁸ m/s) for MP2 and MP3
λ/λ0 = 1.040 for both lines for MP2
values to 2 s.f. (0.040) for MP3 but MP2 needs values to at least 3 s.f.
Do not accept
'the lines are different colours' with no reference to proportion
the galaxy has two velocities
(c)
change in wavelength = 0.040 × 517.3 / evaluation of Δλ = 20.7 (nm);
(λ =) 538.0 (nm);
e.g. Δλ = 0.0400 × 517.3 = 20.7 (nm)
λ = 517.3 + 20.7
Allow
537.9 to 538.1 (nm)
538 (nm)
ECF from ratio in (b)
517.3 × 1.04 for both marks
Do not accept
517.3 + 15.7 or 517.3 + 23.6 (copying one shift) (scores 0)
38IGCSE-PHY-8-039Data: measuring the rotation of a galaxy from red-shiftPaper 2 onlyGrade 8–98 marks
A spiral galaxy is seen edge-on from the Earth. The galaxy is moving away from the Earth and is also rotating about its centre. Astronomers measure the wavelength of a hydrogen line in light from three points on the galaxy: X, C (the centre) and Y. The reference wavelength of this hydrogen line is 656.3 nm. The speed of light is 3.0 × 10⁸ m/s. Point / name: X, C, Y Observed wavelength / nm: 664.7, 664.0, 663.3
(a)
Explain why the wavelength observed from X is longer than the wavelength observed from Y.
(3)
(b)
Determine the speed at which the edge of the galaxy is rotating about its centre.
(4)
(c)
Explain why the astronomers needed to measure the wavelength at the centre C as well as at X and Y.
(1)
Show mark scheme
(a)
galaxy rotating so X is moving away from the Earth and Y towards the Earth (relative to the centre);
X has the greater velocity away from the Earth (recession velocity);
39IGCSE-PHY-8-040Red-shift of a quasar: reference wavelength and observed frequencyPaper 2 onlyGrade 8–99 marks
A quasar is a very distant, very bright object at the centre of a galaxy. A spectral line in the light from a quasar is observed at a wavelength of 529.9 nm. The quasar is moving away from the Earth at 2.7 × 10⁷ m/s. The speed of light is 3.0 × 10⁸ m/s.
(a)
Determine the reference wavelength of this spectral line.
(4)
(b)
Light from galaxy G has a fractional change in wavelength, Δλ/λ0, of 0.030. State and explain whether the quasar or galaxy G is further from the Earth.
(2)
(c)
Calculate the frequency of the light in this spectral line when it is received on the Earth. State how this frequency compares with the frequency of the light emitted by the quasar.
We use essential cookies to make this site work. With your permission we'd also use analytics and advertising cookies to understand which resources help students most and how families find us. Nothing optional is set unless you accept. Privacy policy
EssentialNeeded for the site and your cookie choice to work.
Always on
AnalyticsAnonymous visit statistics that help improve the free resources.
MarketingMeasures whether ads reach the right families. Off unless you turn it on.