EduNinja
(a)

The radiant flux intensity of the radiation from the star in (b) is 2.52×10−8Wm−22.52 \times 10^{-8} \mathrm{Wm}^{-2} when observed at a distance of 4.16×1016 m4.16 \times 10^{16} \mathrm{~m} from the star.

[ 2 ]
(i)

Calculate the luminosity of the star. Give a unit with your answer.
luminosity = unit

[ 2 ]
(a)

A student observes different stars from the Earth.
Give two reasons why some stars appear brighter than others.
1
2

[ 2 ]
(b)

State what is meant by a standard candle.

[ 1 ]
(a)

State what is meant by the luminosity of a star.

[ 1 ]
(b)

A star in the constellation Canis Major is a distance of 8.14×1016 m8.14 \times 10^{16} \mathrm{~m} from the Earth and has a luminosity of 9.86×1027 W9.86 \times 10^{27} \mathrm{~W}. The surface temperature of the star is 9830 K .

[ 2 ]
(i)

Calculate the radiant flux intensity of the radiation from the star observed from the Earth. Give a unit with your answer.
radiant flux intensity = unit

[ 2 ]
(a)

The Sun has a surface temperature of 5780 K . The luminosity of the Sun is 3.85×1026 W3.85 \times 10^{26} \mathrm{~W}.

[ 2 ]
(i)

The Earth is a distance of 1.50×1011 m1.50 \times 10^{11} \mathrm{~m} from the Sun.

Calculate the radiant flux intensity F of the radiation from the Sun at a distance of 1.50×1011 m1.50 \times 10^{11} \mathrm{~m}. Give a unit with your answer.

F=

unit

[ 2 ]
(a)
(i)

State what is meant by the luminosity of a star.

[ 2 ]
(ii)

Explain how a standard candle in a distant galaxy can be used to determine the distance of the galaxy from an observer.

[ 3 ]
(b)

The Sun has a radius of 6.96×108 m6.96 \times 10^{8} \mathrm{~m} and a surface temperature of 5780 K . Light from the Sun is observed to have a peak intensity at a wavelength of 501 nm .

[ 2 ]
(i)

Calculate the luminosity of the Sun. Give a unit with your answer.

luminosity =

unit

[ 2 ]
(a)

A star has a luminosity that is known to be 4.8×1029 W4.8 \times 10^{29} \mathrm{~W}. A scientist observing this star finds that the radiant flux intensity of light received on Earth from the star is 2.6nWm−22.6 \mathrm{nW} \mathrm{m}^{-2}.

[ 3 ]
(i)

Name the term used to describe an astronomical object that has known luminosity.

[ 1 ]
(ii)

Determine the distance of the star from Earth.

distance =
[ 2 ]
(a)

A cosmology student observes the electromagnetic radiation received from a star in a galaxy. The student uses Wien's law to estimate the surface temperature of the star, a standard candle to estimate the distance to the galaxy, and the Stefan-Boltzmann law to estimate the radius of the star.

The student observes that the radiation from the star is redshifted.

[ 1 ]
(i)

State what is meant by a standard candle.

[ 1 ]
(a)

A star of luminosity 3.8×1031 W3.8 \times 10^{31} \mathrm{~W} is a distance of 1.8×1024 m1.8 \times 10^{24} \mathrm{~m} from the Earth.

Calculate the radiant flux intensity at the Earth of the radiation emitted by the star.
radiant flux intensity = Wm−2\mathrm{Wm}^{-2}

[ 2 ]
(a)

A star of luminosity 3.8×1031 W3.8 \times 10^{31} \mathrm{~W} is a distance of 1.8×1024 m1.8 \times 10^{24} \mathrm{~m} from the Earth.

Calculate the radiant flux intensity at the Earth of the radiation emitted by the star.
radiant flux intensity = Wm−2\mathrm{Wm}^{-2}

[ 2 ]
(a)

State what is meant by luminosity of a star.

[ 1 ]
(b)

The luminosity of the Sun is 3.83×1026 W3.83 \times 10^{26} \mathrm{~W}. The distance between the Earth and the Sun is 1.51×1011 m1.51 \times 10^{11} \mathrm{~m}.

Calculate the radiant flux intensity F of the Sun at the Earth. Give a unit with your answer.

unit
[ 2 ]
0