Name: ________________________


                                        Student Number: ______________

Pressure pushing out and Gravity pulling in

as well as

Energy Generation in the interior and Energy Loss from the surface

2. (3 pts) Luminosity and Internal Structure
If the insulating ability of a star increases, its luminosity will
(a) increase.
(b) decrease.
(c) not change.

3. (3 pts) Pressure
Pressure is a force exerted by many
(a) closely packed particles (atoms, nuclei and electrons)
(b) expanding particles (atoms, nuclei and electrons)
(c) hot particles (atoms, nuclei and electrons)
(d) colliding particles (atoms, nuclei and electrons)
(e) cold particles (atoms, nuclei and electrons)

4. (3 pts) Thermodynamics
When the core of a star expands, the core becomes
(a) a white dwarf.
(b) a red giant.
(c) warmer.
(d) denser.
(e) cooler.

5. (4 pts) Sources of Energy
Why was gravitational contraction rejected as the primary source of energy for stars?

Gravitational contraction, down to the size of the present sun, can NOT supply enough energy to keep the Sun losing energy at its present rate for as long as the age of the oldest rocks on Earth

6. The temperature at the center of the Sun is 15 million K and the temperature at the surface of the Sun is 5750 K. What is the typical type of photon emitted at the center of the Sun and what is the typical type of photon emitted at the surface of the Sun?

(3 points) Center:
(a)X-rays
(b)Ultraviolet
(c)Visible
(d)Infrared
(e)Radio

(3 points) Surface:
(a)X-rays
(b)Ultraviolet
(c)Visible
(d)Infrared
(e)Radio

(3 points) What happens to the photon emitted at the center that changes it to the type of photon emitted at the surface that we see?

(a)The photons lose energy and change their type while they fly directly from the center to the surface of the Sun and escape.
(b)The photons emitted from the surface are unrelated to the photons emitted in the center.
(c)The photons slow down as they try to escape from the gravity of the Sun.
(d)The photons emitted from the center of the Sun escape directly through the surface, but we can not see them because they have too much energy.
(e)The photons are absorbed and reemitted with slightly less energy many times as they make their way from the center to the surface.

7. (4 points) Look at the stars Vega and Arcturus in the HR Diagram figure 15-9 in your textbook. Which star is hotter?

Arcturus ___
Vega _X_

Which star is more luminous?

Arcturus _X_
Vega ___