Magnets at the Next Level: Fields, Electromagnets, and Limits

Start with a fair-test mindset. In Curiosity: Textbook of Science for Grade 6, Chapter 4 (Exploring Magnets), you met attraction and repulsion. Now compare strength fairly: change one variable at a time, keep the magnet, paper clips, surface, and method the same, and record results.

A home investigation could ask: How does distance change the number of paper clips a magnet can hold? Use a small stack of identical paper clips, a ruler, and one bar magnet. Touch the magnet to the first clip, then lift gently; record how many clips stay. Repeat at 0 cm, 0.5 cm, 1 cm, 1.5 cm, and 2 cm, three times each. Example pattern (not a universal law):

Distance	Trial 1	Trial 2	Trial 3	Average
0 cm	8	9	8	8.3
0.5 cm	5	4	5	4.7
1 cm	2	2	3	2.3
1.5 cm	0	1	0	0.3
2 cm	0	0	0	0

Evidence: the pull drops sharply as distance grows. Doubling the gap does not just halve the force; for small magnets it usually falls much faster, which is why a paper clip that is close sticks but one a little farther away does not.

Use the same fair-test plan for barriers: keep distance fixed, insert one material at a time such as paper, cardboard, plastic, a water-filled plastic bag, or a steel sheet. For damage tests, compare identical magnets: keep one untouched as a control, drop another ten times, and with an adult's help and safety goggles, gently heat or hammer a third. For poles, count clips on the north pole and the south pole. In an undamaged bar magnet, both poles should hold about the same number; if one is weaker, the magnet may be damaged or unevenly shaped. For field mapping, place a compass at points around a magnet and draw the needle direction at each point.

Domains and why iron differs. In iron, nickel, and cobalt, tiny regions called domains act like groups of aligned atomic magnets. In an unmagnetised piece of iron, the domains point in many directions and their effects cancel. When you stroke iron with a magnet, some domains align, and the whole piece becomes a magnet. Heating, dropping, or hammering can shake the domains into random directions, weakening the magnet. The domain model is useful, but it is a model: domain boundaries are not fixed little bricks, and the model does not explain every magnetic behaviour.

Earth as a magnet. Earth behaves like a giant magnet. A compass needle's north end points toward Earth's magnetic pole near the geographic North Pole. That means Earth's magnetic pole near the geographic North Pole is actually a magnetic south pole, because opposite poles attract.

Electromagnets. When current flows through a coil of wire, it creates a magnetic field. An iron core inside the coil strengthens the field. More turns and more current generally make a stronger electromagnet. This is the reverse idea from Electricity explained: How electricity is generated, where moving a magnet near a coil can generate current. A compass, a fridge magnet, and a motor all rely on magnetic fields: the compass follows Earth's field; the fridge magnet uses a permanent field; a motor uses the push between an electromagnet's changing field and a permanent magnet. A loudspeaker also uses this push, as described in Loudspeaker.

Wider contexts. Maglev trains use magnetic repulsion or attraction to float the train above the track, reducing friction. MRI scanners use very strong magnetic fields and radio waves to image soft tissue. Hard drives store data in tiny magnetic regions. Recycling plants use electromagnets to lift iron and steel from mixed waste. Some animals, including birds, turtles, and bees, appear to sense Earth's magnetic field to navigate, though the exact sensor is still an open question.

History. People in ancient times found lodestone, a naturally magnetised rock. William Gilbert studied Earth's magnetism in the 1600s. Hans Christian Oersted noticed that an electric current could move a compass needle, connecting electricity and magnetism.

What magnets cannot do. Magnets cannot attract all metals; aluminium and copper do not stick. Magnets cannot cure diseases, and magnetic bracelets or healing magnets do not have strong scientific evidence for health claims. Magnets also cannot do work for free; an electromagnet needs a current, and a permanent magnet does not create unlimited energy.