The same magnet can be a weak toy or a serious clamp. The difference is the magnetic circuit — the path the magnetic field takes through the magnet, the steel around it, and the air in between. Arrange it well, and a tiny magnet can out-pull a bare magnet several times its size.
Field lines take the easy road
Magnetic field lines (flux) always take the path of least resistance. Steel gives them an easy ride; air does not. That is why every design question comes back to two ideas:
- Give the flux a steel path. A steel shell or plate lets the field loop back efficiently instead of leaking into the air.
- Keep air gaps tiny. Air is the bottleneck. A 1 mm gap between magnet and target can resist the field more than a metre of steel — which is why a magnet held a few millimetres from a steel plate falls off almost immediately.
Three classic setups
- Bare magnet: flux spreads everywhere, so much of it is wasted. Cheap and fine for light jobs.
- Pot magnet (a magnet inside a steel cup): the steel gathers the flux onto one face. Huge holding force for the size — but it drops fast with distance.
- Multi-pole magnet: many small north/south poles on one face make the flux close inside the target. This is how flexible fridge magnets get their surprising grip.
Why this matters for you
When a magnet “isn't strong enough”, the first suspects are the circuit: is there a steel return path? How big is the air gap? Are the surfaces flat and clean? A coat of paint or a thin gap can quietly halve the holding force. Fix the circuit before buying a bigger magnet — often you do not need one.
Read on: Pc and operating point → · Halbach arrays →