What is a solenoid? Draw the field lines of a current-carrying solenoid. How can it be used to make an electromagnet?
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Define. A solenoid is a coil of many circular turns of insulated copper wire wound closely in the shape of a cylinder.
2 · Draw the field. [Solenoid with battery and key; parallel lines inside; curved lines outside; ends marked N and S; arrows on all lines]
3 · Describe the field.
Like a bar magnet: one end N, the other S.
Inside: parallel straight lines, so the field is uniform.
Reversing the current swaps the poles.
4 · Make an electromagnet. Place a soft iron rod inside the solenoid. The strong field inside magnetises it, and it stays magnetic only while current flows.
5 · Make it stronger.
More turns
More current
Soft iron core
6 · Real life. Electric bells and scrap-yard cranes use electromagnets.
7 · Close in one line. A solenoid with a soft iron core is a magnet you can switch on and off with current.
Scoring tip: The diagram carries most of the marks: parallel lines inside, arrows on every line, and N and S labelled.
