Case 1 — Lost Compass
Rahul used a small compass during his nature walk. When he placed the compass near a large magnet kept in a school lab, the needle pointed away from geographic north and towards the magnet.
Q. Explain why the needle pointed towards the magnet.
A. The magnet produced a stronger local magnetic field than Earth's field; the compass needle aligned with the nearby magnet's field instead of Earth's field.
Case 2 — Iron Filing Pattern
A teacher places a bar magnet under a sheet of paper and sprinkles iron filings. The filings form curved lines that are denser at the ends.
Q1. What do the dense clusters at the ends represent?
A. These show stronger magnetic fields at the poles where field lines are closer together.
Q2. Why do filings form lines instead of random scatter?
A. Filings align along field lines because each tiny piece becomes a small magnet and orients with the field direction, forming visible curves.
Case 3 — Magnetised Needle Compass
Sima magnetises a needle by stroking it with a strong magnet and floats it on cork in water. The needle points in one direction consistently.
Q. How does this simple compass show direction?
A. The magnetised needle aligns with Earth's magnetic field; the end pointing towards geographic north is the north-seeking pole of the needle, showing direction.
Case 4 — Coin Test
A student tests several coins with a magnet. Some coins stick, others do not.
Q. Why do some coins stick to the magnet while others don't?
A. Coins made of or containing iron/steel are magnetic and stick; coins made of non-magnetic metals like copper or aluminium do not.
Case 5 — Broken Magnet
A bar magnet accidentally breaks into two pieces during a demonstration.
Q. What will be the pole structure of the two pieces? Explain.
A. Each piece becomes a complete magnet with both a North and a South pole because magnetic poles always occur in pairs; cutting doesn't produce single poles.
Case 6 — Paper Clip Chain
A magnet lifts one paper clip, which then holds another paper clip, forming a small chain.
Q. Why can the magnet lift many clips in a chain?
A. The magnet magnetizes the first clip (temporary magnet), which attracts the second clip, and so on; the pull weakens with distance, limiting chain length.
Case 7 — Refrigerator Magnet
A decorative magnet holds a note on the fridge door for months without losing strength.
Q. What type of magnet is the fridge magnet and why does it retain magnetism?
A. It's a permanent magnet made from materials that retain domain alignment; manufacturing and material choice lock in magnetism for long use.
Case 8 — Magnet and Electronics
A student places a strong magnet near an old cassette and finds data is erased.
Q. Why did the magnet erase the cassette data?
A. Magnetic storage media store information magnetically; a strong external magnet disturbs the stored magnetic patterns, erasing or corrupting data.
Case 9 — Temporary Magnet in Switch
An electromagnet in a simple circuit attracts a soft iron piece only when current flows, acting as a switch.
Q. Why does the iron piece act like a magnet only when current flows?
A. The electromagnet produces a magnetic field when current passes through the coil; the soft iron becomes temporarily magnetized and is attracted only while the field exists.
Case 10 — Compass Near a Magnet
During a science fair, a compass placed near a display magnet shows a wrong direction to visitors using it to navigate.
Q. What advice would you give to someone using a compass near strong magnets?
A. Keep the compass away from large magnets and electronic devices; move to an open area away from magnetic interference before taking bearings.
Case 11 — Magnetic Separation
A recycling facility uses magnets to remove metal scraps from a conveyor of mixed waste.
Q. How does magnetic separation help recycling and what are its limits?
A. Magnets attract ferrous metals (iron/steel) allowing removal and recycling, improving purity. Limits: non-ferrous metals (aluminium, copper) are not separated and fine metal dust or coated particles may reduce efficiency.
Case 12 — Demagnetising a Magnet
A magnet loses strength after being dropped several times in the workshop.
Q. Explain why the magnet lost strength and how to avoid it.
A. Mechanical shocks disturb magnetic domains causing partial demagnetization. Avoid dropping, store with keepers or spacers, and protect from strong heat to preserve strength.
Case 13 — Needle Magnetised by a Student
A student magnetizes a needle and uses it to pick up small pins. Later the needle stops picking pins as effectively.
Q. Why did the needle's magnetic strength reduce and what can be done to improve it?
A. Needle lost induced magnetism over time due to thermal motion or poor initial magnetisation. Re-stroke with a strong magnet in one direction to re-magnetize it; use harder steel for longer retention.
Case 14 — Field Between Two Magnets
Two bar magnets are placed with north of one near south of the other and then reversed with north near north.
Q1. Describe the field when north faces south.
A. Field lines connect between opposite poles, showing strong attraction and dense field between them.
Q2. Describe what happens when north faces north.
A. Field lines oppose each other; magnets repel and field between them weakens or shows complex patterns with divergence.
Case 15 — Magnet and Paper Clip Through Paper
A student tests whether a magnet can attract a paper clip through several sheets of paper.
Q. Will the paper clip be attracted through paper and why?
A. Yes, magnetic forces act through non-magnetic materials like paper; attraction depends on strength and distance — more paper increases separation and reduces force.
Case 16 — Magnets in Toys
A toy uses small magnets to make parts snap together easily.
Q. Explain the safety considerations for toys with small magnets.
A. Small magnets can be swallowed; swallowing multiple magnets is hazardous. Ensure toys keep magnets enclosed, age-appropriate labeling, and supervise young children.
Case 17 — Speaker Demonstration
In class, a teacher shows how a speaker converts electrical signals into sound using a magnet and a coil.
Q. Briefly explain how the magnet and coil in a speaker produce sound.
A. Electrical signals through the coil create changing magnetic forces that push and pull the cone attached to the coil; cone vibrations create sound waves we hear.
Case 18 — Magnetic Compass in Pocket
A student keeps a compass in a pocket next to a mobile phone and later finds it pointing incorrectly.
Q. Why might the compass give wrong readings and how to fix it?
A. Mobile phones contain magnetic components and can disturb compass needles. Keep compass away from phones and strong magnets; recalibrate by moving to open area and rotate to check again.
Case 19 — Magnetic Latch
A cabinet uses a magnetic latch that keeps the door closed until pulled with force.
Q. How does the magnetic latch keep the door closed and why might it fail over time?
A. A magnet attracts a metal strike plate keeping door closed. Over time demagnetization or misalignment can reduce holding force; dust or wear may also affect performance.
Case 20 — Classroom Demo Gone Wrong
During a demo, two strong magnets snap together quickly, pinching a student's finger.
Q. What safety lessons can be learned and how should such demonstrations be handled?
A. Use protective gloves, keep small strong magnets away from children, demonstrate at safe distances with tools (tongs), warn students of pinch risks, and keep first aid ready. Plan demonstrations to minimise sudden contact.