AQA GCSE Combined Science: Trilogy Physics Paper 2 (Higher), 2021: Question 5

✅ Correct answer

Different temperatures emit different intensities of infrared radiation, and the camera shows these as different shades or colours.

💡 Key knowledge

• All objects emit infrared radiation.
• Hotter objects emit more infrared radiation.
• The camera detects the infrared and converts it into a visible image using shades/colours.

🧠 Exam technique

For 2 marks, you need both ideas:

1. temperature changes the intensity of infrared emitted
2. the camera displays this as different shades/colours

❌ Common errors

• Saying the camera “measures heat directly” — it detects infrared radiation.
• Saying different parts have different “brightness” without linking it to intensity of infrared.
• Forgetting the camera converts the signal into colours/shades.

✅ Correct answer

Visible light

💡 Key knowledge

Infrared has wavelengths from 700 nm to 1 mm. 6.5 × 10⁻⁷ m = 650 nm , which is shorter than 700 nm, so it is in the visible range.

🧠 Exam technique

Always convert units first. If you do not convert nm to m or vice versa, it is easy to choose the wrong section of the spectrum.

❌ Common errors

• Choosing infrared because the number looks “small”.
• Forgetting that 1 nm = 10⁻⁹ m .
• Not checking the infrared lower limit of 700 nm.

✅ Correct answer

Both X-rays and gamma rays are ionising radiation, so both can damage cells and increase the risk of cancer. Gamma rays are generally riskier because the whole body is irradiated and the exposure time is longer. With X-rays, only part of the body is exposed.

💡 Key knowledge

• Ionising means they can remove electrons from atoms/molecules, damaging cells.
• Damage to DNA can lead to mutations and cancer.
• Gamma-ray imaging involves a radioactive isotope in the blood, so radiation comes from inside the body.
• X-ray imaging uses a machine to send a short burst at the target area only.

🧠 Exam technique

This is a compare question, so you must mention both methods. Strong answers compare:

1. the radiation type risk: both are ionising
2. the body area exposed: gamma rays affect the whole body, X-rays only part
3. the exposure time: gamma rays last longer

❌ Common errors

• Saying one is “safe” — both carry risk.
• Missing the idea that gamma rays can expose the whole body.
• Not using the word ionising.
• Writing only similarities or only differences, not a comparison.

📐 Calculation

Given:

• Work done = 1.2 × 10⁻¹³ J
• Distance = 15 mm = 0.015 m

Formula: Work done = Force × distance

Rearrange: Force = Work done ÷ distance

Answer: F = 1.2 × 10⁻¹³ ÷ 0.015 = 8.0 × 10⁻¹² N

💡 Key knowledge

• Use SI units: work in joules, distance in metres, force in newtons.
• 15 mm must be converted to 0.015 m.
• Final answer should be given to 2 significant figures here, matching the data.

🧠 Exam technique

1. Write the formula first.
2. Substitute the numbers clearly.
3. Show the unit conversion.
4. Check the final unit is N.

❌ Common calculation traps

• Using 15 instead of 0.015.
• Forgetting the division and multiplying instead.
• Leaving the answer in joules or millimetres.
• Rounding too early and losing accuracy.

✅ Correct answer

When the electrons hit the tungsten target, some of their energy is transferred to heating. Tungsten has a very high melting point, so it can get very hot without melting. This means more electrons can be collided with the target per second, so more energy per second can be transferred and the X-ray machine can be more powerful.

💡 Key knowledge

• Not all kinetic energy becomes X-rays; much of it becomes thermal energy.
• A target in an X-ray tube must withstand high temperatures.
• Tungsten is suitable because it has the highest melting point of any metal.

🧠 Exam technique

To reach full marks, link the material property to the effect on the machine:

1. electron collisions cause heating
2. tungsten does not melt easily
3. therefore more electrons can hit the target each second / more energy per second can be transferred

❌ Common errors

• Saying tungsten “creates more X-rays” without explaining the heating issue.
• Talking only about “being strong” without mentioning the high melting point.
• Missing the idea of more collisions per second or more energy per second.

💡 Must-know facts

• Infrared cameras show temperature by detecting different infrared intensities.
• 6.5 × 10⁻⁷ m is visible light.
• X-rays and gamma rays are both ionising and can increase cancer risk.
• Gamma imaging usually exposes the whole body for longer.
• Force = work done ÷ distance
• Tungsten is used because it can withstand very high temperatures.

🧠 How to score well

• Use the correct science word: intensity, ionising, melting point.
• For compare questions, always give both sides.
• For calculations, show units and conversions.
• For explanation questions, link cause → effect → result.