Revision sheet · night-before
Exploring Magnets
Read top to bottom — it follows the order of the chapter. Tick each section off as you finish it.
1 · Natural vs artificial magnets
- Lodestone = natural magnet, discovered in ancient times; used by olden-day sailors.
- Artificial magnets — lab magnets, pencil boxes, stickers, toys; first made from iron pieces.
- Shapes: bar, U-shaped, ring, disc, cylindrical, spherical — every shape has two poles.
2 · Magnetic or not?
| Magnetic | Non-magnetic |
|---|---|
| Iron, nickel, cobalt (and some combinations) — steel pins, U-clips, iron nails | Wood, rubber, plastic, glass, paper, cardboard |
3 · Poles
- Iron filings cling most at the ends → poles; very few in the middle.
- Two poles: North and South. Break a magnet → every piece still has both.
- Pole markings: N/S letters, a white dot on North, or red = North, blue = South.
4 · Directions and the compass
- Freely suspended magnet → rests north–south. Reason: Earth behaves like a giant magnet.
- An iron bar rests in any direction → suspension test tells a magnet from iron.
- Compass: needle magnet on a pin, rotates freely, red end points North, dial below, transparent cover.
- Use: let needle settle → rotate the box until dial N–S matches the needle.
- Home-made compass: stroke needle 30–40 times, same pole, same direction → cork → bowl of water.
- Matsya-yantra: magnetised fish-shaped iron in a vessel of oil.
5 · Attraction and repulsion
The most-asked rule in the chapterLike repel, unlike attract.
| Poles brought together | Result |
|---|---|
| N – N | Repulsion |
| S – S | Repulsion |
| N – S / S – N | Attraction |
| Either pole – iron bar | Attraction (always) |
The sure testRepulsion proves something is a magnet; attraction alone does not.
6 · Through materials, and safety
- Wood, cardboard, plastic, glass in between → no appreciable change: magnetism acts through non-magnetic materials.
- Safety: don't heat, drop or hammer; keep away from mobile phones and remote controls.
- Storage: pairs, unlike poles on the same side, wood between, soft iron pieces across the ends.
7 · 10 facts most likely to be asked
- Magnetic materials: iron, nickel, cobalt.
- A magnet always has two poles — they exist in pairs.
- Iron filings stick most at the poles, least in the middle.
- A freely suspended magnet rests north–south.
- Earth behaves like a giant magnet.
- Like poles repel; unlike poles attract.
- Repulsion is the sure test for a magnet.
- Magnetism acts through non-magnetic materials.
- Lodestone = natural magnet; matsya-yantra = Indian fish-shaped compass in oil.
- Store magnets in pairs, unlike poles on the same side, with soft iron across the ends.
Common mistakes to avoid
Don't lose marks here
- Saying "all metals are magnetic" — only iron, nickel, cobalt (and some combinations) are.
- Saying a broken magnet gives a "North-only piece" — every piece has both poles.
- Saying the middle of a bar magnet is strongest — it is the weakest; the poles are strongest.
- Using attraction to prove an object is a magnet — iron is attracted too; only repulsion proves it.
- Thinking glass, wood or plastic "block" magnetism — the effect passes through them.
- When magnetising a needle, rubbing back and forth — you must stroke in one direction with the same pole, lifting the magnet each time.