Topic 5.5: Fusion and Stars Questions

State one assumption made when estimating a star's main-sequence lifetime from t = E ÷ L.

State the difference between the luminosity of a star and its apparent brightness.

A main-sequence star has a mass roughly equal to that of the Sun.

State the type of object this star leaves behind at the very end of its life.

Two main-sequence stars are observed.

Star P glows blue-white and Star Q glows orange-red.

State, with reference to Wien's displacement law, which star has the higher surface temperature.

State what is meant by nuclear fusion.

A star has a measured parallax angle of 0.040 arc-seconds.

Calculate the distance to the star, in parsecs.

When light nuclei fuse, the heavier product nucleus has slightly less mass than the nuclei that formed it.

Identify the source of the energy released by the reaction.

A bright star is plotted in the top-right region of a Hertzsprung-Russell diagram, where the surface temperature is low but the luminosity is very high.

State the type of this star.

An astronomer measures the parallax angle of the star Velora to be 0.025 arc-seconds, observed from opposite ends of Earth's orbit around the Sun.

What is the distance to Velora?

A main-sequence star has a mass of about twelve solar masses.

Identify the correct order of stages it passes through from the main sequence to the end of its life.

A red giant's black-body spectrum peaks at a wavelength of λ_{max} = 700 nm.

Calculate the surface temperature of the star.

(Wien's constant = 2.9 × 10⁻³ m K.)

A fusion reaction in a star's core has a mass defect of Δm = 0.025000 u.

(a) Determine the energy released by one such reaction, in joules.

(b) State how this energy would change if the mass defect were doubled. (1 u = 1.661 × 10⁻²⁷ kg; c = 3.00 × 10⁸ m s⁻¹.)

In the core of a star, light nuclei fuse into a heavier nucleus.

The combined mass of the fusing nuclei exceeds the mass of the product by Δm = 0.026500 u.

Calculate the energy released by this reaction, in MeV.

(1 u = 931.5 MeV c⁻².)

The black-body spectrum of a star is found to peak at a wavelength of about λ_{max} = 385 nm.

Show that the surface temperature of the star is approximately 7500 K.

(Wien's constant = 2.9 × 10⁻³ m K.)

A particular star is observed from two different planets.

The star appears much fainter when seen from the more distant planet, even though it is the same star.

Explain this observation in terms of luminosity and apparent brightness.

Two main-sequence stars, P and Q, each have the same amount of fusible hydrogen, worth E = 1.6 × 10⁴⁴ J of energy.

Star P has luminosity L_P = 2.0 × 10²⁶ W and star Q has luminosity L_Q = 8.0 × 10²⁶ W.

(a) Deduce which star has the longer main-sequence lifetime.

(b) Determine the ratio of their lifetimes, t_P ÷ t_Q.

Outline how the parallax method is used to determine the distance to a nearby star.

Over its main-sequence life a star radiates a total energy of about E = 2.5 × 10⁴⁴ J.

Estimate the total mass the star loses by radiating this energy.

(c = 3.00 × 10⁸ m s⁻¹.)

A star has a luminosity of 4.0 × 10²⁸ W and is at a distance of 5.0 × 10¹⁸ m from Earth.

Calculate the apparent brightness of the star as observed from Earth.

A main-sequence star has a mass of about one solar mass, and a second main-sequence star has a mass of about twenty solar masses.

(a) State the sequence of stages each star passes through from the main sequence to the end of its life.

(b) Explain why the two stars end their lives so differently.