Spectra & Evidence for an Expanding Universe — Drills · Grade 9 Science

Chapter: Stars & the Universe

What these drills covers

By the end of Spectra & Evidence for an Expanding Universe you should be able to:

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

Vocabulary used: spectrum, redshift, cosmic microwave background, light-year, megaparsec (Mpc).

Problem 1

A 600 nm line is observed at 630 nm. Find z.
Answer and explanation

0.05

30 ÷ 600 = 0.05.

Problem 2

Name an independent observation besides galaxy redshifts supporting the Big Bang model.
Answer and explanation

The cosmic microwave background or the observed abundances of light elements.

Problem 3

Light from distant galaxies is shifted toward the red end of the spectrum, which indicates they are
  1. approaching
  2. receding
  3. stationary
  4. hotter
Answer and explanation

receding

Redshift corresponds to increasing distance between us and the source.

Problem 4

More distant galaxies generally show
  1. smaller redshift
  2. greater redshift
  3. no redshift
  4. blueshift
Answer and explanation

greater redshift

Recession speed increases with distance, which is the observational basis for expansion.

Problem 5

The cosmic microwave background is
  1. light from nearby stars
  2. faint radiation left from the early universe
  3. heat from Earth
  4. a measurement error
Answer and explanation

faint radiation left from the early universe

It is thermal radiation released when the universe first became transparent.

Problem 6

Spectral lines identify elements in a star because each element
  1. has a unique pattern of wavelengths it absorbs or emits
  2. is a different colour
  3. has the same spectrum
  4. cannot be detected
Answer and explanation

has a unique pattern of wavelengths it absorbs or emits

The pattern acts as a fingerprint, measurable across enormous distances.

Problem 7

Explain how expansion can be observed from Earth without Earth being at the centre.
Answer and explanation

In a uniformly expanding space every observer sees everything else receding, with more distant objects receding faster, because the space between all points is increasing. The same observation would be made from any galaxy. The pattern therefore shows expansion rather than a special position for us, which is why no centre is implied.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Why is the cosmic microwave background considered strong evidence rather than one observation among many?
Answer and explanation

It was predicted before it was found, its temperature matches what the model required, and its tiny variations match the structure needed to form galaxies. A prediction confirmed in detail by a later measurement is far stronger evidence than a result a theory was adjusted to fit, which is why it carries particular weight.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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