why are pole pieces of moving coil galvanometer made concave?
Answers
The moving coil of a moving coil galvanometer, moves in a magnetic field produced by a permanent magnet. When a current passes through the coil, its sides which are perpendicular to the magnetic field, experience equal and opposite force. This force is separated by the width of the coil. These two equal and opposite forces seperated by the width of the coil constitute a couple, which rotates the coil.
We want the current carrying coil to be always perpendicular to the magnetic field, even when it has rotated. The magnetic field produced by concave shaped pole faces is always radial. A radial field is always perpendicular to a conductor rotating about a axis passing through the centre of the concave shaped pole faces and parallel to the faces.
Explanation:
The moving coil of a moving coil galvanometer, moves in a magnetic field produced by a permanent magnet. When a current passes through the coil, its sides which are perpendicular to the magnetic field, experience equal and opposite force. This force is separated by the width of the coil. These two equal and opposite forces seperated by the width of the coil constitute a couple, which rotates the coil.
We want the current carrying coil to be always perpendicular to the magnetic field, even when it has rotated. The magnetic field produced by concave shaped pole faces is always radial. A radial field is always perpendicular to a conductor rotating about a axis passing through the centre of the concave shaped pole faces and parallel to the faces.
Pole faces are concave to make the magnetic field radial to keep it always normal to the moving coil.