A ship uses a search-and-rescue device that contains a coil of wire connected to a detector. When the device is held near a submerged metal object, the changing magnetic field from the object induces a potential difference in the coil. Explain how electromagnetic induction produces a potential difference in the coil and describe two ways the size of the induced potential difference could be increased.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A ship uses a search-and-rescue device that contains a coil of wire connected to a detector. When the device is held near a submerged metal object, a changing magnetic field passes through the coil.
Model answer (4 marks)
A changing magnetic field passing through the coil induces a potential difference.
The potential difference is produced because the magnetic field lines linking the coil change, which cuts the field lines and creates an emf.
The induced emf can be increased by:
1. Increasing the number of turns of wire in the coil.
2. Increasing the strength of the magnetic field (e.g. using a stronger magnet or moving the field source closer or faster).
The potential difference is produced because the magnetic field lines linking the coil change, which cuts the field lines and creates an emf.
The induced emf can be increased by:
1. Increasing the number of turns of wire in the coil.
2. Increasing the strength of the magnetic field (e.g. using a stronger magnet or moving the field source closer or faster).
Examiner tips
- Use the phrase "changing magnetic field" and "induced potential difference". Show the two methods: more turns and stronger field. Keep answer concise and to the points.
Common mistakes
- Forgetting that the field must change. Describing emf as caused by current instead of changing flux. Mentioning only one method to increase emf.
Mark scheme (4 marks)
- A changing magnetic field (passing through the coil) induces a potential difference / the magnetic field must be changing to induce a potential difference
- The induced potential difference is due to the change in the magnetic field cutting through / linking with the coil (lines of magnetic field passing through the coil change)
- First method to increase induced potential difference: increase the number of turns/coils of wire
- Second method to increase induced potential difference: increase the strength of the magnetic field / use a stronger magnet or move the source of the field closer / faster
Key terms in this question
electromagnetic induction · induced potential difference · coil · magnetic field
Related
- All OCR GCSE Physics A: Gateway Science (J249) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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