Stars & The Universe (Cambridge (CIE) IGCSE Physics)

The Sun is our nearest star.

(i) State the three main forms of electromagnetic radiation emitted by the Sun.

[2]

(ii) State the two main elements that are found in the Sun.

[1]

State and explain what can be deduced from the ‘redshift’ observed by astronomers in the light from all distant galaxies.

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Describe and explain how a stable star is formed.

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Describe and explain what can be deduced from cosmic microwave background radiation (CMBR).

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Some main sequence stars become black holes. 

Describe the evolution of a main sequence star to the point at which it becomes a black hole. 

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State and explain whether the Sun will eventually become a black hole. 

The visible part of the electromagnetic spectrum from a star includes a dark line. This line is at a specific wavelength.

Fig 1.1 shows the position of the dark line in the spectrum from the Sun and in the spectrum from two different galaxies, galaxy A and galaxy B.

Explain what the spectrum ‘shifts’ of the dark lines tells us about the direction of the galaxies.

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State which galaxy is:

(i) is moving faster.

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(ii) is further away.

[1]

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Galaxy A is 150 000 × 10⁹ m away.

Calculate its recession velocity.

Hubble constant = 2.2 × 10^–18 per second.

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A galaxy C is twice as far as galaxy A.

Determine the recession velocity of galaxy C.

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Describe nuclear fusion in stars.

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Derive the distance of 1 light year in metres.

Speed of light = 3.0 × 10⁸ m/s

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The Milky Way is approximately 100 000 light years in diameter.

Calculate the time it would take a spacecraft travelling at the speed of light to travel from one side of the Milky Way to the other.

 time = ......................................... s 

Below are some statements related to Cosmology.

1. Galaxies are made of up millions of stars

2. The Sun is a planet because it has a core

3. Other stars that make up the Milky Way are much further away from the Earth than the Sun is from the Earth

4. There may be other galaxies in the Milky Way

State all of the statements that are false and explain why.

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Edwin Hubble was an American scientist who studied galactic recession.

Define the Hubble constant, H₀.

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State the current value of the Hubble constant.

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The Andromeda galaxy is the Milky Way's largest galactic neighbour. The Andromeda galaxy is approximately 2.5 million light years from Earth.

Calculate the speed with which the Andromeda galaxy is receding from Earth. You should give your answer in km/s.

............................................................... km/s

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State and explain the two pieces of evidence which support the Big Bang Theory of the origin of the Universe.

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Calculate the distance of 50 light-years in metres.

Speed of light = 3.0 × 10⁸ m/s.

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Redshift measurements show that a galaxy is receding from Earth at a speed of 32 000 km/s. 

Use Hubble's Law to calculate how many light-years the galaxy is distant from the Solar System.

Take the Hubble constant to be 2.2 × 10^-18 per second.

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Explain what type of radiation the CMBR will eventually change into over the next billion years.

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Scientists measure the wavelength of the radio waves from galaxy A travelling at 260 km/hr away from Earth to be 63.2 m. Sometime later, the wavelength is measured to be 63.4 m.

The wavelength of the radio waves from galaxy B is initially measured to be 63.4 m and at the same time later, measured to be 63.8 m.

Calculate the velocity of galaxy B.

velocity of galaxy B  = ...................................... m/s 

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By measuring the redshift of galaxies, Hubble was able to calculate the speed at which they move away from the Earth. Hubble was also able to calculate the distance of these galaxies from the Earth.

The graph in Fig 1.1 shows some of the data calculated by Hubble.

Fig 1.1

The graph in Fig 1.1 was used to calculate the most up-to-date value of the Hubble constant, H₀. 

Megaparsecs are a unit for large distances commonly used in Astronomy and Cosmology. 1 megaparsec = 3.1 × 10²² m.

 Calculate H₀ in km/s megaparsec.

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Show that H₀ is roughly equal to 2.0 × 10^–18 per second.

The ‘big bang’ theory is one theory explaining the origin of the Universe.

Fig 1.1

(i) Sketch the graph of the size of the Universe with time on Fig 1.1.

[2]

(ii) Explain how your graph in part (i) supports the Big Bang Theory.

[2]

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(i) Describe and explain the main properties of CMBR.

[2]

(ii) Explain how CMBR provides evidence for the evolution of the Universe. 

[3]

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Suggest why our understanding of the very earliest moments of the Universe is unreliable.

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Nuclear fusion reactions in the Sun fuse hydrogen to make helium.

In the Solar System, the inner planets, such as the Earth, contain elements which are heavier than the elements hydrogen and helium.

Explain how this can be the case.

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From the data collected, a graph can be drawn that links the speed of a galaxy with the distance of the galaxy from the Earth. This graph is shown in Fig. 1.1.

Fig 1.1

Describe how the visible light spectrum from galaxy Q looks different from the visible light spectrum from galaxy P.

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A third galaxy, R, seems to be travelling away from the Earth at about 110 000 km/s.

Estimate how far galaxy R might be from the Earth, showing how you use the graph in Fig. 1.1 to do this.