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IGCSE · Cambridge (CIE) · 0625

Compare low-orbit and geostationary satellite communication

Connect microwave links to the two listed satellite-phone arrangements and direct-broadcast television.

Electromagnetic spectrum pathway · 3.3

Core and Extended; Physics 0625, 2026–2028. Follow the selected spectrum or sound section. Diagrams illustrate stated ideal models and supplied data. Written practice is self-checked.

Before you begin

  • Explain electromagnetic vacuum propagation.
  • Distinguish a microwave carrier from voice information.

Work on paper. Try each question before revealing help, and explain why your method works.

Quick readiness check

Which carrier is mainly used to communicate with artificial satellites?

What you will learn

  • Identify microwaves as the main satellite communication carrier.
  • Distinguish the listed low-orbit and geostationary uses.
Original unscaled communication sketch contrasts changing apparent positions in low orbit with the fixed apparent direction of a geostationary link. Both use mainly microwaves; some phones use either arrangement and direct-broadcast satellite television uses geostationary satellites. A relay contains an uplink and a downlink.Main carrier: microwavesLow orbit: changing sky position123Some satellite-phone systemsGeostationary: fixed sky positionUplinkDownlinkPhones and direct-broadcast TV
Original unscaled communication sketch contrasts changing apparent positions in low orbit with the fixed apparent direction of a geostationary link. Both use mainly microwaves; some phones use either arrangement and direct-broadcast satellite television uses geostationary satellites. A relay contains an uplink and a downlink.

Choose the correct satellite link

Communication with artificial satellites is mainly by microwaves. Some satellite phones use low-orbit satellites; others use geostationary satellites. Direct-broadcast satellite television uses geostationary satellites. The word 'satellite' alone does not identify the orbit type.

A geostationary satellite appears at a fixed position in the sky relative to a suitable ground location. A receiving television dish can point toward that direction. Low-orbit satellites change their apparent position, so systems use tracking, coverage changes or handover between links.

Separate orbit from propagation

Both arrangements use electromagnetic paths rather than sound crossing space. Orbit choice changes path length and coverage, not the common vacuum speed of a microwave. A longer path can add delay because the signal travels farther.

A diagram of ground → satellite → ground has two path segments. Do not replace the total communication path with satellite altitude or count only the upward segment. Real paths are slanted and real systems include processing; use a supplied ideal path only when stated.

Pause and explain

Which orbit is used for the listed direct-broadcast satellite television arrangement?

Put the idea to work

Worked example

A direct-broadcast television dish points in a fixed direction toward a satellite. Identify the usual carrier and orbit type.

Show the worked solution
  1. The satellite communication carrier is mainly microwave.
  2. Direct-broadcast satellite television uses a geostationary satellite.
  3. Its fixed apparent direction supports the fixed pointing arrangement.

Answer Microwaves and a geostationary satellite.

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Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.

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From guided practice to a new situation

Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.

1 · Guided

Name the main region used for artificial-satellite communication.

Give me a hint

Identify the carrier, not the information content.

Compare my reasoning
  1. The route includes space.
  2. It uses electromagnetic radiation.
  3. The main listed region is microwaves.

Microwaves.

Look for these in your work

  • Name the region.
  • Keep voice separate from carrier.
2 · Independent

List the two stated satellite-phone arrangements and the television orbit.

Give me a hint

Do not force all satellite applications into one orbit.

Compare my reasoning
  1. Some phones use low-orbit satellites.
  2. Some phones use geostationary satellites.
  3. Direct-broadcast satellite television uses geostationary satellites.

Phones: low orbit or geostationary; direct-broadcast TV: geostationary.

Look for these in your work

  • Include both phone cases.
  • Identify the television case.
3 · Transfer

An ideal relay has an upward path of 40 000 km and downward path of 38 000 km. What path length should a later delay calculation use?

Give me a hint

Add both stated travel segments.

Compare my reasoning
  1. The wave travels 40 000 km upward.
  2. It then travels 38 000 km downward.
  3. Total path = 78 000 km, not one altitude.

78 000 km total relay path.

Look for these in your work

  • Count both legs.
  • Do not infer an orbital altitude from the supplied path lengths.

Common mistakes

  • Some satellite phones use each listed orbit type.
  • Orbit does not change vacuum wave speed.
  • A relay route includes both path segments.
Recall without your notes

What can you explain now?

Do all satellite phones use geostationary satellites?

Compare with the explanation

No.

Some use low-orbit satellites; some use geostationary satellites.

After trying it yourself, choose your next review. This is your self-assessment.

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Make it stick

Describe satellite carriers, the two phone orbit arrangements and the direct-broadcast television orbit.

If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.

Keep learning Physics

Course scope and assessment

491 sequenced Physics lessons provide 1473 guided, independent and application problems. 58 of 58 syllabus sections have full linked teaching sequences; 0 sections remain pending. Three earlier starter overviews remain available but are not counted as full sequences. The map covers all six subject areas for 2026–2028 and keeps review and assessment limits visible. This is available content, not full programme completion, an exam grade or certified mastery. Written practice is self-checked. Supervised practical experience, cumulative assessment and human subject-teacher review remain pending. Paper method exercises do not demonstrate practical competence or complete either practical-assessment route.

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