AQA A Level Physics Astrophysics
Exam Questions with Answers
Definition parsec - Answer>> the distance to an object
subtending 1 second of arc to the radius of the Earth's orbit.
(1 second of arc (arcsecond) = 1/3600 of a degree).
Units parsec - Answer>> pc
Definition light year - Answer>> Distance light travels in a
vacuum in 1 year.
(number of seconds in 1 year = 365 x 24 x 60 x 60 = 3.15x107s
Units light year - Answer>> ly
Definition astronomical unit - Answer>> The mean distance
between the Earth and the Sun
Units astronomical unit - Answer>> AU
Definition of absolute magnitude - Answer>> The brightness an
object would appear if it was 10 parsecs from the Earth.
Definition of apparent magnitude - Answer>> The brightness of
an object as seen from Earth
What is black body radiation? - Answer>> The electromagnetic
radiation emitted by an object because of its temperature
General shape of black body curves - Answer>> Temperature
is DECREASING going from P to R.
, Area under curve is total power output per m2 (as given by
Stefan's Law)
You need to able to sketch these curves
Definition λmax - Answer>> The wavelength at which maximum
emission occurs.
Assumption about a star to use Wein's displacement law (λmax) -
Answer>> Star is acting as a black body.
Effect of atmosphere on estimate of a star's temperature -
Answer>> • Ozone in atmosphere preferentially absorbs UV
part of spectrum
• This increases observed λmax (longer wavelength)
• Resulting in an underestimate of the star's temperature
Definition of intensity - Answer>> energy arriving every second
on a 1 m² surface orientated perpendicular to the direction of
radiation
Units of intensity - Answer>> Wm-2
Relation between intensity and apparent magnitude - Answer>>
Each change in magnitude of 1 (on the magnitude scale)
corresponds to a change in intensity of 2.51 .
So a star which has a magnitude that is 5 times brighter than
another star, has an intensity which is 100 times greater (2.515 =
100).
Inverse square law and assumptions in its application -
Answer>> the intensity I at a distance r from a star with a total
power output P, is given by
Intensity I = P/4πr²
Exam Questions with Answers
Definition parsec - Answer>> the distance to an object
subtending 1 second of arc to the radius of the Earth's orbit.
(1 second of arc (arcsecond) = 1/3600 of a degree).
Units parsec - Answer>> pc
Definition light year - Answer>> Distance light travels in a
vacuum in 1 year.
(number of seconds in 1 year = 365 x 24 x 60 x 60 = 3.15x107s
Units light year - Answer>> ly
Definition astronomical unit - Answer>> The mean distance
between the Earth and the Sun
Units astronomical unit - Answer>> AU
Definition of absolute magnitude - Answer>> The brightness an
object would appear if it was 10 parsecs from the Earth.
Definition of apparent magnitude - Answer>> The brightness of
an object as seen from Earth
What is black body radiation? - Answer>> The electromagnetic
radiation emitted by an object because of its temperature
General shape of black body curves - Answer>> Temperature
is DECREASING going from P to R.
, Area under curve is total power output per m2 (as given by
Stefan's Law)
You need to able to sketch these curves
Definition λmax - Answer>> The wavelength at which maximum
emission occurs.
Assumption about a star to use Wein's displacement law (λmax) -
Answer>> Star is acting as a black body.
Effect of atmosphere on estimate of a star's temperature -
Answer>> • Ozone in atmosphere preferentially absorbs UV
part of spectrum
• This increases observed λmax (longer wavelength)
• Resulting in an underestimate of the star's temperature
Definition of intensity - Answer>> energy arriving every second
on a 1 m² surface orientated perpendicular to the direction of
radiation
Units of intensity - Answer>> Wm-2
Relation between intensity and apparent magnitude - Answer>>
Each change in magnitude of 1 (on the magnitude scale)
corresponds to a change in intensity of 2.51 .
So a star which has a magnitude that is 5 times brighter than
another star, has an intensity which is 100 times greater (2.515 =
100).
Inverse square law and assumptions in its application -
Answer>> the intensity I at a distance r from a star with a total
power output P, is given by
Intensity I = P/4πr²
