Magnetic Field Around a Wire
- When a current flows through a conducting wire a magnetic field is produced around the wire
- A conducting wire is any wire that has current flowing through it
- The shape and direction of the magnetic field can be investigated using plotting compasses
- The compasses would produce a magnetic field lines pattern that would like look the following
Diagram showing the magnetic field around a current-carrying wire
- The magnetic field is made up of concentric circles
- A circular field pattern indicates that the magnetic field around a current-carrying wire has no poles
- As the distance from the wire increases the circles get further apart
- This shows that the magnetic field is strongest closest to the wire and gets weaker as the distance from the wire increases
- The right-hand thumb rule can be used to work out the direction of the magnetic field
The right-hand thumb rule shows the direction of current flow through a wire and the direction of the magnetic field around the wire
- Reversing the direction in which the current flows through the wire will reverse the direction of the magnetic field
Side and top view of the current flowing through a wire and the magnetic field produced
- If there is no current flowing through the conductor there will be no magnetic field
- Increasing the amount of current flowing through the wire will increase the strength of the magnetic field
- This means the field lines will become closer together
In my experience of teaching the right-hand thumb rule (and the left-hand rule), students can feel a little embarrassed that they may have to use it in the exam. My advice to them is always, no one will be looking at what you are doing in the exam. Everyone will be so busy focusing on their own work they won't even notice, and it's true! I have taken many exams, and I have invigilated many as well. Time passes so quickly in exams that everyone is only focused on finishing their paper before the time runs out.