AQA GCSE Combined Science: Trilogy Physics Paper 2 (Foundation), June 2025: Question 5

✅ Correct Answer

Tick: Microwaves

💡 Key Knowledge

Certain frequencies of microwaves pass straight through the Earth's upper atmosphere (ionosphere) without being reflected or absorbed, making them ideal for communication with geostationary satellites.

❌ Common Errors

Selecting gamma rays (dangerous ionising radiation, not used for broad communications) or visible light (scattered easily by clouds and rain in atmosphere-to-space links).

Mark allocation: 1 mark for ticking "Microwaves". Any other tick scores 0.

✅ Correct Answer

Tick: Gamma rays

💡 Key Knowledge

The EM spectrum in order of increasing frequency (and photon energy):

Radio → Micro → Infrared → Visible → UV → X-rays → Gamma

Gamma rays have the shortest wavelength and the highest frequency.

❌ Common Errors

Confusing wavelength with frequency. Radio waves have the longest wavelength, whereas gamma rays have the highest frequency.

🧠 Exam Technique

Remember the mnemonic: Raging Martians Invaded Venus Using X-ray Guns. The right-hand end has the highest frequency and hazard level!

✅ Correct Answer

Tick: The time taken for one wave to pass a fixed point

💡 Key Knowledge

• Period (T): Time for one complete wave cycle (measured in seconds).
• Frequency (f): Number of waves passing per second (measured in Hertz).
• Wave Speed (v): Distance travelled by a wave crest in one second (m/s).

❌ Common Errors

Selecting "The number of waves passing a fixed point each second" — this is the definition of frequency, not period.

🧠 Exam Technique

Look at the units: Period is measured in seconds, which is a unit of time. The definition must refer to "the time taken".

Step 1: Convert gigahertz (GHz) into hertz (Hz)
The prefix 'giga' means 10⁹ (1 billion):
48 GHz = 48 × 10⁹ Hz (or 48 000 000 000 Hz ) [1 mark]

Step 2: Select the equation and substitute
From the physics equation sheet: Period = 1 / frequency ( T = 1 / f )
T = 1 / 48 000 000 000 [1 mark]

Step 3: Calculate the numerical answer
T = 2.083... × 10⁻¹¹ (accept 2.1 × 10⁻¹¹ or 0.000 000 000 021 ) [1 mark]

Step 4: Select the correct unit from the box ( J , N/kg , s )
Period is time, so the unit is s (seconds). [1 mark]

❌ Common Traps

• Missing the prefix: Calculating 1 / 48 = 0.021 scores partial credit via Error Carried Forward (ECF), but loses the conversion mark.
• Unit error: Selecting J (joules - energy) or N/kg (gravitational field strength).
• Calculator input error: Forgetting brackets when typing 1 / (48 × 10⁹) .

🧠 Top Tip for Full Marks

Always check your standard form powers on negative exponents. Very high frequencies ( 10⁹ Hz ) must produce extremely small periods ( 10⁻¹¹ s ).

✅ Correct Answer (give any ONE)

• Speed (travel at the same speed in a vacuum / air: 3 × 10⁸ m/s )
• They can all travel through a vacuum (do not require a medium)
• They all transfer energy
• They are all transverse waves

❌ Common Errors

• Stating "they have the same wavelength" or "same frequency" (the question explicitly mentions different frequencies!).
• Writing just "speed" without ensuring it's clear — while "speed" alone is accepted, writing "speed in air/vacuum" is best practice.

✅ Acceptable Answers (give any ONE)

• Cables may not reach remote / rural / isolated areas.
• It is too expensive / difficult / impractical to lay underground cables over long or difficult terrain (e.g. mountains, islands).
• Satellites may provide faster connection than old copper lines in areas where fibre cables do not exist.

🧠 Exam Technique

Whenever an exam asks why a wireless/satellite system is used over physical cables, think about geography and cost of installation. Laying miles of underground fibre to reach only a handful of remote farmhouses is not economically viable.