A bell that rings itself
A gate bell rattles while a finger stays on the button.
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Step 1 of 3
- Circuit closed. The coil pulls the arm across.
- The arm hits the gong. It also breaks the contact.
- A spring pulls the arm back. The contact closes again.
The rule
An electric bell has an electromagnet. Pressing the button closes the circuit.
The arm is an iron strip near the coil. The gong is the metal part that rings. With the button pressed, current flows while the arm touches the screw. That touch is the contact.
The coil pulls the arm, and the arm hits the gong. The same move breaks the contact. The coil lets go, because no current flows.
A spring pulls the arm back. The contact closes, so current flows again. The steps repeat while you press the button. So the bell keeps ringing.