When describing stars

PHYSICS · Multi-part · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter

Problem

1. When describing stars, state what is meant by the term *luminosity*,

L

? 2. Assuming a star to be a black-body radiator, with a surface temperature

T

and a radius

R

at a distance

d

from the Earth, write a mathematical expressions for the luminosity,

L

, of the star. 3. Using the Stefan–Boltzmann constant of

\sigma = 5.67 \times 10^{-8} \text{ Wm}^{-2} \text{ K}^{-4}

, calculate the luminosities of the following stars (you may assume that they are black bodies): - i** Star A, radius

7 \times 10^8 \text{ m}

, surface temperature 5700 K - ii** Star B, radius

8.2 \times 10^{11} \text{ m}

, surface temperature 3500 K. - iii** Star C, radius

4.9 \times 10^{10} \text{ m}

, surface temperature 11 200 K. (1) When describing stars, state what is meant by the term *luminosity*,

L

? (2) Assuming a star to be a black-body radiator, with a surface temperature

T

and a radius

R

at a distance

d

from the Earth, write a mathematical expressions for the luminosity,

L

, of the star. (3) Using the Stefan–Boltzmann constant of

\sigma = 5.67 \times 10^{-8} \text{ Wm}^{-2} \text{ K}^{-4}

, calculate the luminosities of the following stars (you may assume that they are black bodies): - i** Star A, radius

7 \times 10^8 \text{ m}

, surface temperature 5700 K - ii** Star B, radius

8.2 \times 10^{11} \text{ m}

, surface temperature 3500 K. - iii** Star C, radius

4.9 \times 10^{10} \text{ m}

, surface temperature 11 200 K. (4) The luminosity of our Sun is

3.8 \times 10^{26} \text{ W}

. For each of the stars in part c, give their luminosities relative to the luminosity of the Sun,

L_{\odot}