Red-shift (AQA GCSE Physics)

What is the Universe?

What name is given to the theory that the Universe started with a giant explosion?

What are the main ideas of this theory?

What is thought to be happening to the size of the Universe?

State and explain briefly, one piece of scientific evidence which may be used to support this belief.

Explain, in as much detail as you can, the main scientific evidence supporting the big bang theory of the Universe.

Astronomers use special telescopes that can detect different types of electromagnetic waves to observe the Universe.

Why is it important that we use the entire electromagnetic spectrum to study the Universe?

What is meant by red-shift?

In 2005 astronomers discovered a star with the biggest red-shift ever detected.

What does this tell us about this star?

The Big Bang theory is a theory about the origin of the Universe.

Explain how the light arriving from distant galaxies provides important evidence in support of this theory.

In 1998 some astronomers produced some evidence that suggested that some of the ideas scientists had about the Universe was incorrect.

What should scientists do when a theory does not appear to be supported by new data?

Although scientists have studied how the Universe was created, they do not know why the Universe was created.

Suggest a reason why this question cannot be answered by scientists.

Binary stars are pairs of stars that both move around a common point.

Figure 1 below shows one star in a binary system at two positions in its orbit.

Figure 1

The spectrum of light coming from the stars contains some dark lines known as absorption lines. The position of these lines in the spectrum is shown in Figure 2 for the two positions above, along with the same lines in the Sun’s spectrum.

Figure 2

These spectra provided important information about the movement of this star in the binary system.

Explain how.

The light emitted from most galaxies is red-shifted relative to similar light observed on Earth.

What does red-shift tell scientists about the direction most galaxies are moving?

The size of this red-shift is different for different galaxies.

What information about a galaxy can be found out by measuring the size of its red-shift?

What do the above observations suggest is happening to the Universe?

The table in Figure 3 below shows the distance to several galaxies along with the speeds at which they are moving away from us.

The final column shows the time for which the galaxies have been moving, which has been calculated using the formula:

Figure 3

Complete the data for galaxy C.

Describe the relationship between the speed of a galaxy and the distance the galaxy is from us.

The data in the fourth column (time) provides evidence supporting the idea that the Universe was created in a big bang.

Explain how.

Redshift can be used to determine whether a star is moving away from or towards the Earth. 

State and explain what is meant by 'redshift' in this context.

In a laboratory, hydrogen is found to emit light of wavelength 656.61 nm. The spectrum of a star observed on Earth is found to have the same line in the spectrum shifted to 656.68 nm.

The following equation can be used to calculate the redshift:

Where:

• = change in observed wavelength

• = wavelength observed in the laboratory

• = speed of the galaxy

• = speed of light = 3.0 × 10⁸ m/s

(i) Use the equation to calculate the speed of the star relative to the Earth.  

speed of the star = ................................... m/s  [4]

(ii) Explain whether the star is moving towards or away from the Earth.

[2]

A second spectral line is observed at 567.34 nm in the laboratory. 

Determine the frequency of the spectral line from the star, as observed on Earth.

 Frequency = ......................................... Hz

Explain the effect on the colour of light from the star if it were travelling towards the Earth.

Define redshift.

The shift in wavelength can be identified using spectral lines in an absorption spectrum.

The following absorption spectrum is generated using light from a source in a laboratory:

Sketch the spectrum obtained using light from a galaxy moving away from the Earth.

Redshift can be calculated using:

Where

• = wavelength

• = frequency

• = velocity of the galaxy

• = speed of light = 3.0 × 10⁸ m/s

An absorption line in the spectrum of light from a source in a lab in part (b) has a frequency of 5.783 × 10¹⁴ Hz. The same line in the spectrum of light from a distant galaxy has a frequency of 5.791 × 10¹⁴ Hz.

Calculate the speed of the distant galaxy in relation to the Earth.

The Big Bang theory suggests that the Universe is approximately 14 billion years old.

Describe the evolution of the Universe from the Big Bang until the present day.

Describe the evidence for dark energy and dark matter.

Describe the observations of distant galaxies compared to closer galaxies and discuss what this tells us about the universe.

In 1929, the astronomer Edwin Hubble noticed that the majority of galaxies in the Universe are moving away from us.

The graph in Figure 1 shows some of the data that was collected by Hubble.

Describe the relationship between speed and distance shown by the best fit line in Figure 1.

Hubble determined the speed of galaxies by measuring the red-shift of dark lines in the light being emitted by the galaxies.

Explain how red-shift affects the wavelength and frequencies of these lines as observed from the Earth.

The gradient of the best fit lines gives the value of an important quantity known as the Hubble Constant.

Use the graph in Figure 1 to calculate a value for the Hubble constant.

Show clearly how you obtained your answer.

Hubble constant =................................ km/s per MPc

Astronomers have continued to take measurements of the speeds and distances of galaxies, and have used these measurements to calculate more accurate values of the Hubble Constant.

The graph in Figure 2 below shows some more recent data. 

Using Figures 1 and 2, explain why the value of the Hubble constant given by this more recent data can be considered to be more accurate than Hubble’s original value.

Figure 1 below shows the spectrum of light received on the Earth from the Sun and from a star in a distant galaxy.

Figure 1

The spectrum contains some characteristic dark lines, which occur at very specific wavelengths in the laboratory.

Explain how the shift in the position of the dark lines provides evidence to support the Big Bang theory.

The data in Figure 1, along with data from other galaxies, can be used to plot a graph showing how the shift in position changes with the distance of each galaxy from the Earth, as shown in Figure 2.

A new galaxy is discovered with a red-shift of 0.02.

Using the graph in Figure 2, estimate the distance to this new galaxy.

Show clearly how you obtained your answer

State an assumption you made in obtaining the answer to part (b).