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IGCSE · 6 · structured

Space physics · Question 7

Space physics · Original GioPhysics question with a detailed, mark-by-mark answer guide.

Demand
routine
Marks
6
Topics
1
Answer
Complete
The Earth orbiting the Sun and the Moon orbiting the EarthSunEarthMoondashed lines show the orbits — not to scale
Fig. 7.1A not-to-scale plan view of the Sun, the Earth and the Moon. The Sun is a disc at the centre of a large dashed circle, and the Earth is a smaller disc sitting on that circle to the right of the Sun. A second, much smaller dashed circle is drawn around the Earth with the Moon on it, up and to the right of the Earth. A short arrow on each dashed circle shows the direction in which the Earth travels around the Sun and the Moon around the Earth.
structured6 marks

The Earth spins on its own axis and also orbits the Sun. The Moon orbits the Earth, taking about one month to complete an orbit.

  1. (a)

    State State the approximate time taken for one rotation of the Earth on its axis, and for one orbit of the Earth around the Sun.

    2 marks
  2. (b)

    Explain Explain why the Moon can be seen from Earth even though it produces no light of its own.

    2 marks
  3. (c)

    Explain The Sun is much further from the Earth than the Moon is, yet the Sun and the Moon appear almost the same size in the sky. Explain how this is possible.

    2 marks
Ready to self-mark?Reveal the detailed answer guide
Answer overviewKey answer: rotation: 24 hours (1 day) orbit: 365 days (1 year) light from the Sun falls on the Moon
01

(a)

2 marks

State State the approximate time taken for one rotation of the Earth on its axis, and for one orbit of the Earth around the Sun.

How to approach it

Answer the command word directly and use precise physical vocabulary. Include only the distinct features or facts that earn marks, without burying them in unrelated background information.

  1. 1

    rotation: 24 hours (1 day)

  2. 2

    orbit: 365 days (1 year)

02

(b)

2 marks

Explain Explain why the Moon can be seen from Earth even though it produces no light of its own.

How to approach it

State the outcome first, then link cause to effect with the relevant physical principle. Each link in the reasoning should be explicit enough to earn its own marking point.

  1. 1

    light from the Sun falls on the Moon

  2. 2

    and is reflected from the Moon's surface to the Earth

03

(c)

2 marks

Explain The Sun is much further from the Earth than the Moon is, yet the Sun and the Moon appear almost the same size in the sky. Explain how this is possible.

How to approach it

State the outcome first, then link cause to effect with the relevant physical principle. Each link in the reasoning should be explicit enough to earn its own marking point.

  1. 1

    the Sun's diameter is very much larger than the Moon's — about 400 times larger

  2. 2

    and the Sun is about 400 times further away, so the two subtend almost the same angle at the Earth

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