Topic 5.5: Fusion and Stars Questions

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.

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

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

State what is meant by nuclear fusion.

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

Calculate the distance to the star, in parsecs.

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

Astronomers measure the parallax angle of a nearby star to be 0.018 arc-seconds.

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.)

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 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.

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

Two stars are marked on an H-R diagram.

Star R has luminosity 3600 L_sun and surface temperature 4640 K.

The Sun has surface temperature 5800 K.

Determine the radius of Star R as a multiple of the Sun's radius.

Use R_star/R_sun = (T_sun/T_star)² × √(L_star/L_sun).

A Sun-like star, Solara-F, has mass M = 1.9 × 10³⁰ kg.

About 13% of its mass is fusible core hydrogen, and 0.70% of that fusible mass is released as energy.

Its luminosity is L = 3.8 × 10²⁶ W.

Show that its main-sequence lifetime is about 1.3 × 10¹⁰ years.

(c = 3.00 × 10⁸ m s⁻¹; 1 year ≈ 3.16 × 10⁷ s.)