If a wire is carrying electric current it generates a magnetic field around itself. The higher the current, the stronger the field. Some people believe that this field is a health hazard, particularly around high voltage
distribution lines, but research into the topic has been unable to demonstrate any risk so far.
If the current is travelling along a long straight wire the field looks like this (below).
Magnetic field in a current carrying conductor (right hand screw rule)
- A conductor carrying current creates magnetic field around it.
- The strength of the magnetic field can be increased by increasing the current. In IGCSE course we are only interested in finding the direction of this magnetic field.
- In order to determine the direction of the magnetic field around a current carrying conductor we apply right hand screw rule. According to this rule if a right-hand thumb held in a way that it is pointing towards the direction of the conventional current (means flow of positive charges from positive terminal to negative terminal of the battery), then the direction of rotation of the fingers gives the direction of the magnetic field (N-S) around the conductor.
Magnetic field due to solenoid (right hand grip rule)
- Solenoid is a long cylindrical coil with number of turns. It produces magnetic field similar to that of a bar magnet.
- In solenoid the direction of the magnetic field can be found by applying the right hand grip rule.
- According to this rule if the fingers of the right hand grip the solenoid in the direction of the flow of conventional current, the thumb points towards the north pole.
- Higher the number of turns or larger the current in the coil, it gives the stronger magnetic field.
- Permanent magnets can be made by allowing molten ferromagnetic metals to solidify in such solenoid fields.
- Relays and electric bells are the good example of use of magnetic field due to a current carrying conductor.