AQA GCSE Physics Physics Paper 1 (Foundation), November 2021: Question 5

✅ Correct Answer

Atomic number

💡 Key Knowledge

• The atomic number (proton number) defines what element an atom is. Every atom of the same element has the exact same number of protons.

❌ Common Errors

Confusing atomic number with mass number or neutron number, both of which can vary between atoms of the same element (isotopes).

✅ Correct Answer

Number of neutrons

💡 Key Knowledge

• Isotopes are atoms of the same element (same protons/atomic number) that have different numbers of neutrons, leading to a different mass number.

🧠 Exam Technique

Read carefully: make sure you look for what is different for isotopes, not what is the same.

✅ Correct Answer

Alpha

💡 Key Knowledge

• An alpha particle consists of 2 protons and 2 neutrons (a helium nucleus, ₄₂He).
• During alpha decay, the atomic number decreases by 2 and the mass number decreases by 4. Looking at graph D: atomic number drops from 88 to 86, and mass number drops from 226 to 222.

❌ Common Errors

Guessing beta emission without checking how atomic and mass numbers change on the graph axes.

✅ Correct Answer

Beta

💡 Key Knowledge

• During beta decay, a neutron turns into a proton and a high-speed electron (beta particle) is emitted.
• The atomic number increases by 1, while the mass number stays exactly the same. On graph E, the atomic number increases from 90 to 91 while mass number stays at 236.

🧠 Exam Technique

Memorise the nuclear equations for decay types: Alpha loses 4 from mass / 2 from atomic; Beta adds 1 to atomic / mass unchanged.

✅ Correct Answer

1. decrease
2. increase

💡 Key Knowledge

• If paper gets thicker, it absorbs more beta radiation.
• Less radiation reaches the detector behind the paper, meaning the detector reading decreases.

❌ Common Errors

Mixing up detector readings with absorption rates. Remember: more material in the way = more absorption = lower detector reading.

✅ Correct Answer

The time it takes for the count rate of a sample to halve.

💡 Key Knowledge

• Half-life is defined as the time taken for the activity (or count rate / number of radioactive nuclei) of a source to fall to half its initial value.

❌ Common Errors

Stating it is the time for all nuclei to decay, or confusing it with physical distance ranges in air.

✅ Correct Answer

So the activity of the source is approximately constant.

💡 Key Knowledge

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• Industrial thickness monitors need to run for long periods without frequent calibration or source replacements. A long half-life ensures the emitted radiation level remains steady over time.

🧠 Exam Technique

Relate practical uses to physical properties: medical tracers need short half-lives to limit patient exposure, while industrial gauges need long half-lives for consistency.