A relay is a switch flipped by a magnet. A solenoid is a magnet that pulls an iron rod. Both are just a coil of wire with current flowing through it.
Coil supply0.0 V
Multimeter (Ω) · supply must be off for coil
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Coil current: 0 mA
Why use a relay?A tiny current (30 mA) in the coil safely switches a big current in the load circuit. The two circuits never touch: the magnet links them.
Think of it like…A railway point switch. The train (load current) goes one way (NC) until a small push from the coil flips the points, and then it goes the other way (NO).
Relay (12 V coil)
Parameter
Rated
Measured
Status
Ammeter
0.00 A
Load on the hook
50 g
Coil heat
Think of it like…A fridge magnet you can turn up. More volts push more current through the coil (I = V ÷ R), and more current makes a stronger magnet that lifts more weight.