Build An Electric Door Bell
We learnt about electromagnets probably at the beginning of our high school. The definition, if my memory serves me well, is when an insulated coil is wound around iron piece and the when the current is flown through this coil, a magnetic field is created. Note the word - insualated coil and we will come to this later again.
The physics book also had few practical purposes of this electromanget and one of them is the electric door bell. The door bells we currently get in the market are electronic door bells and they do not have any electromangnets - they instead have a musical circuit. We can cover this too sometime in a later post.
Circuit
Please have a look into the circuit below. It is the simplest form of a circuit to build an electric door bell. And this is exactly what I built when I was 12. Did it work? No it didn’t. But will it work? Yes, it will. Let’s read ahead.
What we need
| Sr. No | What we need | What I did |
|---|---|---|
| 1 | A nail | A cycle wheel spoke and bent it into an U |
| 2 | Insulated coil | Pulled copper wire from a cable |
| 3 | Gong | From my cycle bell |
| 4 | Batteries | From a flash light (torch) |
| 5 | Spring | From a ball point pen |
| 6 | A thin rod | Another spoke of the same cycle wheel |
| 7 | Connectors | Nails/screws |
How does it work
As we know, then current is flown through the coil a magentic field is created. Here the circuit starts from the battery (B) to the U shaped spoke (U), then into the vertical thin rod (R) and finally closes the circuit via the connector (C).
This is a closed circuit and creates a magnetic field which attracts the rod R towards it. In that process, it hits the gong (G). But the moment the rod is attracted towards the electromagnet, the connection between rod (R) and the connecter (C) breaks, leaving the circuit open.
When the circuit is open, there is no electromagnetism. At this moment, the spring (S) pull the rod (R) back. When the rod (R) is back to its position, it creates contact with the connector (C) resulting a closed circuit and we get the magnetic field again. This process gets into a loop.
Simple isn’t it? To make the entire circuit sturdy, I fixed them all into a wooden plank. After all this effort, it never worked for me. Reason is simple. By definition we need to have an insulated coil, but I used a copper wire. So basically I was shorting the circuit. It took me over two years to understand my mistake when I opened up the cycle dynamo. At that moment, I realised two things - a) an electromagnet is a simple thing and b) I’d be into Physics for the rest of my life.