- The current balance is used to measure the force of repulsion between identical, oppositely directed, currents in parallel conductors.This shows a direct link between the mechanical forces of Newton and the electromagnetic forces of Ampere and Maxwell.
- This apparatus is extremely delicate and must be handled with a very light touch. The current balance consists of a rectangular conducting frame which cause the current passes by entering and exiting through liquid gallium. The entire frame is suspended by a 0.006-inch diameter high strength torsion wire.
- The rectangular frame is counter-balanced by a long beam having a movable counter-balance mass on it and a magnetically damped vane on its end.The vane also serves as a zero-position indicator. Directly below the long side of the rectangular frame is a parallel conductor carrying the same current in the opposite direction.
- The height of this conductor is adjustable to allow different separations between the conductors. Each end can be lowered or raised independently of the other to make the two conductors parallel.
- The separation adjustment screws have a 1 mm pitch and are used to adjust the centre-to-centre conductor separation from 3.2 mm to 15 mm in increments of 0.05 mm. One end of the torsion support wire is fastened to a rotatable degree dial which can be rotated a total of three revolutions, one-and-a-half revolutions in either direction from the centre equilibrium position.
- The other end of the torsion wire can be rotated only about 200 degrees and is used to make fine adjustments in the zero equilibrium position. The torsion balance has a sensitivity of about 3 degrees per milligram of force.
- A change of less than 2 degrees on the degree dial is discernible. The balance has a 20 Amp fuse to protect the equipment from damage.Good measurements can be made with a current of 5 A and a maximum working current of 15 A is recommended.
Instrument Name: Current Balance