Using an electromagnet, you can make a working model of a railway

signal as shown in Fig.14.26.

1. Take a cardboard and make a hold into it.

2. Attach the carbon hole to a stand.

3. Tie a thread to one end of the cardboard and tie an iron nail to the thread.

4. Make an electromagnet and rotate the coil of wire on it. Connect the wire to a battery and a key.

In this way, a railway signal can be made.