A farmer uses an aircraft to spray insecticide over a field. The insecticide droplets are given a static charge as they leave the spray nozzle. Explain how giving the droplets a static charge improves the effectiveness of the spray.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Farmers sometimes use aircraft to spray crops with insecticide. Modern spray systems charge the insecticide droplets as they are released from the nozzle.
Model answer (4 marks)
1. The droplets are given the same electrical polarity, so they all carry like charges.
2. Like charges repel each other, causing the droplets to spread out evenly across the spray pattern.
3. The droplets are attracted to the earth and to the crop, which have opposite charge, pulling them downwards.
4. This attraction and repulsion reduces drift, ensuring the droplets stay on the crop and give more even, complete coverage.
2. Like charges repel each other, causing the droplets to spread out evenly across the spray pattern.
3. The droplets are attracted to the earth and to the crop, which have opposite charge, pulling them downwards.
4. This attraction and repulsion reduces drift, ensuring the droplets stay on the crop and give more even, complete coverage.
Examiner tips
- Use the exact terms ‘like charges’, ‘repel’, ‘attracted’, and ‘coverage’ as the mark scheme expects.
- Show the causal chain: charge → repulsion → spread → attraction → coverage.
- Keep each point concise – one sentence per mark is sufficient.
Common mistakes
- Confusing ‘attract’ with ‘repel’ for like charges.
- Failing to mention that the droplets are attracted to the crop/earth.
- Giving extra detail about the spray nozzle that isn’t asked for.
Mark scheme (4 marks)
- The charged droplets all carry the same polarity / like charges
- Like charges repel, so the droplets spread out evenly / repel each other
- The charged droplets are attracted towards the earth / crop (unlike charges attract)
- This reduces the risk of droplets blowing away / ensures more even / complete coverage of the crop
Key terms in this question
Related
- All Edexcel GCSE Physics (1PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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