# Worksheet: Luminosity

In this worksheet, we will practice calculating the flux density due to the energy radiated by a star at a given distance away from the star.

Q1:

At what distance from the Sun is the flux density equal to 300 W/m2? Give your answer in astronomical units to 3 significant figures. Use a value of m for the length of 1 AU and W for the luminosity of the Sun.

Q2:

The Peony star, which is located near the galactic center, has a luminosity of . At what distance from this star is the flux density equal to the flux density from the Sun at Earth? Use a value of m for the length of 1 AU and W for the luminosity of the Sun. Give your answer in astronomical units to 3 significant figures.

Q3:

Which of the following is the correct unit of luminous flux density?

• AW⋅m
• BW/m
• CW/m2
• DW⋅m2
• EJ/m2

Q4:

The flux density at a distance of 15.6 AU from a star is 89.4 W/m2. What is the luminosity of the star? Give your answer in terms of the luminosity of the Sun to 3 significant figures. Use a value of m for the length of 1 AU and W for the luminosity of the Sun.

• A4.02
• B6.53
• C5.11
• D16.1
• E8.03

Q5:

A star has a luminosity of 4 . What is the flux density from the star at a distance of 3 AU? Use a value of W for the luminosity of the Sun and m for the length of 1 AU. Give your answer to 3 significant figures.

Q6:

A star has a luminosity of W. What is the flux density from the star at a distance of m? Give your answer to 3 significant figures.

Q7:

Star A has a luminosity and star has a luminosity . At a distance away from star and a distance away from star , the flux densities due to each star are equal. What is the ratio ?

• A1
• B2
• C
• D4
• E

Q8:

The flux density at a distance of 0.7 AU from a star is 2,800 W/m2. What is the luminosity of the star? Use a value of m for the length of 1 AU. Give your answer in watts to 3 significant figures.

• A W
• B W
• C W
• D W
• E W

Q9:

The Sun has a luminosity of W. What is the flux density from the Sun at Neptune, a distance of 30.1 AU away from the Sun? Use a value of m for the length of 1 AU. Give your answer to 3 significant figures.

Q10:

Sirius A is a nearby star with a luminosity of W. The luminosity of the Sun, , is W. What is the luminosity of Sirius A in terms of ? Give your answer to 3 significant figures.

• A
• B
• C
• D
• E

Q11:

Which of the following is the correct unit of luminosity?

• AW/m2
• BW/m
• CW
• DJ
• EW⋅m2