AQA A-level PHYSICS Paper 3 Section B Astrophysics June
2025 Question Paper Questions And Correct Making Scheme.
Definition of Principal focus (Focal Point) - 100% correct answer as The point
through which all light parallel to the axis of the lens passes through
Assumption for estimating age of Universe from Hubble's Law -
100% correct answer as Hubble's constant, H, has been constant since the
Big Bang.
Features of Big Bang - 100% correct answer as • Expanding
universe
• from an extremely hot and dense single point
• Suggest about 15 billion years ago (from Hubble's constant)
• "explosion" - creation of space/matter and time
Evidence for Big Bang - 100% correct answer as Redshift of distant galaxies
• In keeping with Hubble's law (see Hubble observations
above).
• Hubble's law can be used to age universe
.
Cosmological microwave background radiation
• If Universe is about 15 billion years old and has been expanding and cooling
since Big Bang.
• would estimate temperature of "empty space" to be a few
Kelvin after this time.
• black body curve of "empty space" corresponds to
temperature of about 2.7 Kelvin (appropriate max)
,• consistent with temperature universe would have cooled to after 15 billion
years
Relative abundance of Helium and Hydrogen
• short time after Big Bang universe hot enough to fuse matter
• Hydrogen fused to form Helium
• Universe continued to expand, and cool
• making fusion of helium into heavier elements impossible
• creating predicted ratio of 3:1 (Hydrogen to Helium)
• consistent with observation of matter in Universe.
Properties of quasars - 100% correct answer as • Originally identified as strong
radio sources (though now known to emit at all parts of em spectrum)
• They have very large red shifts (and hence large distance from
Hubble's law)
• They are very faint (dim apparent magnitudes)
• They are very small (about size of a solar system)
• Application of m-M=5log(d/10), using d calculated from Hubble's law,
suggests they are the brightest objects in the universe (same absolute magnitude
as several galaxies put together)
• Now believed to be super massive black holes at centre of active galaxies
• Most distant measurable objects.
Exoplanets - 100% correct answer as orbit stars other than our sun
only reflect light from the star they orbit, therefore are fainter than star and can be
hard to see as are obscured by star
Exoplanets methods of detection - 100% correct answer as 1. Radial velocity
method
, - Star and exoplanet both have mass, so exert gravitational force on one
another
- centre of mass of system is closer to centre of mass of star as it is larger
- this causes star to 'wobble' - shows as doppler shift
- doppler shift used to calculate radial velocity of star about centre of mass of
system
2. Transit method
- detects dimming of star's brightness as exoplanet moves infront of it ,
perpendicular to our line of sight
- allows radius of exoplanet to be calculated if radius of star is known
- drop in fractional brightness = pir^2planet/ pir^2star = r^2planet/r^2star
=(rplanet/rstar)^2
Definition of Focal length - 100% correct answer as The distance between the
centre of the lens and the focal point.
Formation of images by converging lenses
object beyond 2f - 100% correct answer as image upside down, small
Formation of images by converging lenses
object between F and lens - 100% correct answer as image behind lens,
upright, small
Ray diagram of a refracting telescope in normal adjustment -
100% correct answer as
2025 Question Paper Questions And Correct Making Scheme.
Definition of Principal focus (Focal Point) - 100% correct answer as The point
through which all light parallel to the axis of the lens passes through
Assumption for estimating age of Universe from Hubble's Law -
100% correct answer as Hubble's constant, H, has been constant since the
Big Bang.
Features of Big Bang - 100% correct answer as • Expanding
universe
• from an extremely hot and dense single point
• Suggest about 15 billion years ago (from Hubble's constant)
• "explosion" - creation of space/matter and time
Evidence for Big Bang - 100% correct answer as Redshift of distant galaxies
• In keeping with Hubble's law (see Hubble observations
above).
• Hubble's law can be used to age universe
.
Cosmological microwave background radiation
• If Universe is about 15 billion years old and has been expanding and cooling
since Big Bang.
• would estimate temperature of "empty space" to be a few
Kelvin after this time.
• black body curve of "empty space" corresponds to
temperature of about 2.7 Kelvin (appropriate max)
,• consistent with temperature universe would have cooled to after 15 billion
years
Relative abundance of Helium and Hydrogen
• short time after Big Bang universe hot enough to fuse matter
• Hydrogen fused to form Helium
• Universe continued to expand, and cool
• making fusion of helium into heavier elements impossible
• creating predicted ratio of 3:1 (Hydrogen to Helium)
• consistent with observation of matter in Universe.
Properties of quasars - 100% correct answer as • Originally identified as strong
radio sources (though now known to emit at all parts of em spectrum)
• They have very large red shifts (and hence large distance from
Hubble's law)
• They are very faint (dim apparent magnitudes)
• They are very small (about size of a solar system)
• Application of m-M=5log(d/10), using d calculated from Hubble's law,
suggests they are the brightest objects in the universe (same absolute magnitude
as several galaxies put together)
• Now believed to be super massive black holes at centre of active galaxies
• Most distant measurable objects.
Exoplanets - 100% correct answer as orbit stars other than our sun
only reflect light from the star they orbit, therefore are fainter than star and can be
hard to see as are obscured by star
Exoplanets methods of detection - 100% correct answer as 1. Radial velocity
method
, - Star and exoplanet both have mass, so exert gravitational force on one
another
- centre of mass of system is closer to centre of mass of star as it is larger
- this causes star to 'wobble' - shows as doppler shift
- doppler shift used to calculate radial velocity of star about centre of mass of
system
2. Transit method
- detects dimming of star's brightness as exoplanet moves infront of it ,
perpendicular to our line of sight
- allows radius of exoplanet to be calculated if radius of star is known
- drop in fractional brightness = pir^2planet/ pir^2star = r^2planet/r^2star
=(rplanet/rstar)^2
Definition of Focal length - 100% correct answer as The distance between the
centre of the lens and the focal point.
Formation of images by converging lenses
object beyond 2f - 100% correct answer as image upside down, small
Formation of images by converging lenses
object between F and lens - 100% correct answer as image behind lens,
upright, small
Ray diagram of a refracting telescope in normal adjustment -
100% correct answer as
