Stars, Fusion & Element Formation — Practice · Grade 9 Science

Chapter: Stars & the Universe

What this practice covers

By the end of Stars, Fusion & Element Formation you should be able to:

8 questions, multiple choice and written answer, each with a worked explanation.

Vocabulary used: fusion, main sequence, white dwarf.

Problem 1

The Sun’s main energy source is…
  1. coal combustion
  2. nuclear fusion
  3. reflected moonlight
  4. friction with air
Answer and explanation

nuclear fusion

Hydrogen fusion supplies energy in its core.

Problem 2

How does solar energy cross the near-vacuum to Earth?
Answer and explanation

As electromagnetic radiation.

Problem 3

Why does more stellar fuel not necessarily mean a longer lifetime?
Answer and explanation

A higher-mass star can consume fuel much faster.

Problem 4

Why can a massive star have a shorter main-sequence lifetime than a smaller star? Explain the reasoning in your own words.
Answer and explanation

The larger fuel supply can be consumed disproportionately faster.

Its energy output and fuel-consumption rate can be much greater.

Compare available fuel with the rate of use rather than fuel amount alone.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 5

What distinguishes fusion from chemical burning in a star? Show the reasoning, not just the conclusion.
Hints

Compare supply with consumption rate.

Answer and explanation

Fusion changes nuclei and releases nuclear energy; ordinary chemical reactions rearrange electrons and atoms without that nuclear transformation.

Problem 6

Why does a star's color provide temperature evidence?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Its emitted spectrum depends on surface temperature; bluer stars generally have hotter surfaces than redder ones.

Problem 7

More fuel does not guarantee a longer lifetimeMore fuel does not guarantee a longer lifetimeSupplied relative fuel / rate indicesStar A: available fuel1Star B: available fuel5Star A: use rate1Star B: use rate100Lifetime scale B/A = 5/100 = 0.05 in this model.
Original relative fuel/use-rate model. A and B are invented examples and the index values are not a calibrated stellar mass relation. Full-scale bars make the much greater rate visible; the lifetime inference uses the explicitly supplied normalization and assumptions.
Interpret the supplied visual model. If A’s model lifetime is 10 billion years, what lifetime follows for B under the supplied ratios?
Answer and explanation

0.05×10 billion = 0.5 billion years, or 500 million years. This is a teaching comparison, not a measured lifetime for a named star or all stars of a given mass.

Fuel amount and use rate are unlike kinds of quantity, with separate normalization. Calculate their ratio rather than adding bar heights.

0.05×10 billion = 0.5 billion years, or 500 million years. This is a teaching comparison, not a measured lifetime for a named star or all stars of a given mass.

Response criteria

  • Read the labeled quantities, reference frame or objects correctly.
  • Explain the relation between the visual evidence and the mechanism.
  • Keep the drawing’s stated assumptions and limits in the conclusion.

Problem 8

Model star B has four times A’s available fuel but eighty times its fuel-use rate. Estimate its lifetime relative to A and explain why this is a ratio model rather than a complete stellar-evolution forecast.
Answer and explanation

The ratio is 4/80 = 0.05, so B’s lifetime scale is one twentieth of A’s. Actual evolution also depends on initial mass, composition, core structure and changing conditions; these supplied ratios are not a universal stellar formula.

The ratio is 4/80 = 0.05, so B’s lifetime scale is one twentieth of A’s. Actual evolution also depends on initial mass, composition, core structure and changing conditions; these supplied ratios are not a universal stellar formula.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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