Example
1. A wire carrying a current at right angles to a magnetic field experiences a force. List 3 ways of increasing the size of the force.
2. An electric current flows in a loop of wire in the direction shown in the diagram below. The loop is between the poles of a magnet.
Complete the table below to show which sections of the loop experience a force.
| Section of the loop | Force acting? Yes or No | Direction | Reason |
| AB | Yes | Down | Fleming’s left hand rule |
| BC | |||
| CD |
| Section of the loop | AB |
|---|---|
| Force acting? Yes or No | Yes |
| Direction | Down |
| Reason | Fleming’s left hand rule |
| Section of the loop | BC |
|---|---|
| Force acting? Yes or No | |
| Direction | |
| Reason |
| Section of the loop | CD |
|---|---|
| Force acting? Yes or No | |
| Direction | |
| Reason |
3. What electrical device is based on this arrangement of coil and magnet?
4. What would happen if the north and south poles were reversed?
Answer
1. 3 ways of increasing the size of the force are:
- Increasing the size of the current.
- Using a stronger magnet.
- Increasing the length of wire inside the magnetic field.
2. Completed table:
| Section of the loop | Force acting? Yes or No | Direction | Reason |
| AB | Yes | Down | Fleming’s left hand rule |
| BC | No | The current BC is parallel to the direction of the magnetic field and so experiences no force. | |
| CD | Yes | Up | Using Fleming’s left hand rule the direction of the force is vertically upwards (and opposite to the direction of the force on side AB) |
| Section of the loop | AB |
|---|---|
| Force acting? Yes or No | Yes |
| Direction | Down |
| Reason | Fleming’s left hand rule |
| Section of the loop | BC |
|---|---|
| Force acting? Yes or No | No |
| Direction | |
| Reason | The current BC is parallel to the direction of the magnetic field and so experiences no force. |
| Section of the loop | CD |
|---|---|
| Force acting? Yes or No | Yes |
| Direction | Up |
| Reason | Using Fleming’s left hand rule the direction of the force is vertically upwards (and opposite to the direction of the force on side AB) |
3. An electric motor.
4. The coil would rotate in the opposite direction but at the same speed.