AQA GCSE Combined Science: Trilogy Physics Paper 2 (Higher), 2024: Question 3

💡 Key knowledge

• All electromagnetic waves travel at the same speed in a vacuum.
• They are transverse waves.
• Microwaves are used in satellite and mobile communication.
• Visible light ranges from red to violet; violet has the shortest wavelength.
• High-frequency EM waves can damage cells and increase cancer risk.
• Frequency and period are linked by frequency = 1 ÷ period .

🧠 Exam technique

• Use the exact physics term the mark scheme wants.
• For 2-mark explanations, give two separate clear points.
• For calculations, show the substitution and final answer in standard form.
• Include units every time: Hz for frequency, s for period.

❌ Common errors

• Saying EM waves all have the same wavelength — they do not.
• Describing transverse waves as “up and down” only, without saying the oscillations are perpendicular to the direction of travel.
• Answering “light” instead of “violet” in part 03.4.
• For part 03.6, forgetting to use standard form or calculating the wrong way round.

✅ Correct answer

They all have the same speed in a vacuum.
Also accepted: they all transfer energy.

💡 Key knowledge

Electromagnetic waves can travel through a vacuum, and in a vacuum they all move at the same speed.

🧠 Exam technique

Say one clear property. If you write more than one, that is fine — but the mark is only for a correct idea.

❌ Common errors

Do not say “they can travel through air” as your property — the mark scheme says ignore that.

✅ Correct answer

The oscillations/vibrations are perpendicular to the direction of energy transfer.

💡 Key knowledge

For a transverse wave, the wave moves one way while the vibrations are at right angles to that direction.

🧠 Exam technique

Use the words perpendicular or at right angles. These are the key marking words.

❌ Common errors

“Up and down” alone is not enough unless you also link it to the direction of travel.

✅ Correct answer

Microwaves

💡 Key knowledge

Microwaves are used for satellite communication and also for mobile phone signals.

🧠 Exam technique

One-word answers must be precise. “Radio waves” is sometimes accepted, but “microwaves” is the best answer here.

❌ Common errors

Do not write “infrared” or “visible light” — these are not used for satellite communications.

✅ Correct answer

Violet (also accepted: purple)

💡 Key knowledge

In the visible spectrum, wavelength decreases from red to violet. Violet has the shortest wavelength and highest frequency.

🧠 Exam technique

Remember the order: red → orange → yellow → green → blue → indigo → violet.

❌ Common errors

Students often write “blue” because it is at the short-wavelength end, but the shortest is violet.

✅ Correct answer

Any two of these:
• Ultraviolet, X-rays or gamma rays can damage DNA / cause mutations.
• Ultraviolet can age skin and/or cause skin cancer.
• X-rays or gamma rays can increase the risk of cancer.

💡 Key knowledge

The highest-frequency waves are the most energetic, so they can damage cells and DNA.

🧠 Exam technique

For 2 marks, give two separate risk statements. The safest way is to name the wave and the effect.

❌ Common errors

Simply saying “they are dangerous” is too vague. You need the specific harm: DNA damage, mutations, cancer, skin ageing, or eye damage.

📐 Calculations: step by step

1. Write the formula: frequency = 1 ÷ period
2. Substitute the period: frequency = 1 ÷ (4.0 × 10⁻¹⁰)
3. Calculate: frequency = 2.5 × 10⁹
4. Give the final answer in standard form and include the unit: 2.5 × 10⁹ Hz

✅ Correct answer

2.5 × 10⁹ Hz

🧠 Exam technique

Marks are for the method and the final answer. Even if your calculator does the work, show the equation and substitution clearly.

❌ Common calculation traps

• Using period instead of frequency.
• Forgetting that the answer must be in standard form.
• Leaving out Hz.
• Putting the wrong power of ten because of calculator entry errors.

✅ Correct answer

Radio waves are produced by the transmitter.
The detector absorbs the waves/energy, which produces an alternating current.
The current has the same frequency as the transmitted waves.

💡 Key knowledge

Oscillations in the transmitter create electromagnetic waves. When these waves reach the detector, they are absorbed and converted into an electrical signal.

🧠 Exam technique

To gain full marks, explain the chain: oscillations → EM waves → absorption in detector → alternating current → same frequency.

❌ Common errors

Do not just say “the signal is received”. That is too vague. You need to mention absorption and alternating current.

Examiner focus: students gained marks by making each step explicit. Answers that only mentioned “waves” and “signal” often missed marks because they did not explain how the detector converts the wave into an electrical current.

✅ Know this

• EM waves all travel at the same speed in a vacuum.
• Transverse means vibrations are perpendicular to the direction of travel.
• Microwaves are used for satellite communication.
• Violet has the shortest wavelength in visible light.
• High-frequency EM waves can damage DNA and increase cancer risk.

🧠 How to score full marks

• Use precise keywords from the specification.
• Give two separate points for 2-mark explain questions.
• Show calculator steps for any equation question.
• Write answers in standard form when asked.