Example
The north pole of a magnet is moved into a coil connected to a centre-zero A device used to measure electric current..
The needle deflects to the right.
a) Complete the results table to show the deflection, if any, of the ammeter needle.
| Movement of magnet | Deflection of needle |
| North pole moves towards coil | Right, and then returns to zero |
| Magnet at rest inside coil | |
| North pole moves away from coil | |
| South pole moves towards coil | |
| South pole moves away from coil |
| Movement of magnet | North pole moves towards coil |
|---|---|
| Deflection of needle | Right, and then returns to zero |
| Movement of magnet | Magnet at rest inside coil |
|---|---|
| Deflection of needle |
| Movement of magnet | North pole moves away from coil |
|---|---|
| Deflection of needle |
| Movement of magnet | South pole moves towards coil |
|---|---|
| Deflection of needle |
| Movement of magnet | South pole moves away from coil |
|---|---|
| Deflection of needle |
b) In terms of the electric current what is the difference between a deflection of the ammeter to the right and to the left.
c) List three things that could be done to make the induced current, and hence the deflection of the ammeter, bigger.
Answer
a) The completed table:
| Movement of magnet | Deflection of needle |
| North pole moves towards coil | Right, and then returns to zero |
| Magnet at rest inside coil | No deflection |
| North pole moves away from coil | Left, and then returns to zero |
| South pole moves towards coil | Left, and then returns to zero |
| South pole moves away from coil | Right, and then returns to zero |
| Movement of magnet | North pole moves towards coil |
|---|---|
| Deflection of needle | Right, and then returns to zero |
| Movement of magnet | Magnet at rest inside coil |
|---|---|
| Deflection of needle | No deflection |
| Movement of magnet | North pole moves away from coil |
|---|---|
| Deflection of needle | Left, and then returns to zero |
| Movement of magnet | South pole moves towards coil |
|---|---|
| Deflection of needle | Left, and then returns to zero |
| Movement of magnet | South pole moves away from coil |
|---|---|
| Deflection of needle | Right, and then returns to zero |
b) A deflection of the ammeter to the right and to the left indicates the current changing direction.
When the needle deflects to the right, the current flows in one direction.
When the needle deflects to the left, the current flows in the opposite direction.
c) The induced current, and hence the deflection of the ammeter, could be made bigger by:
- Moving the magnet faster.
- Using a stronger magnet.
- Having more turns of wire in the coil.