Ampere balance

The current scale was developed by André- Marie Ampère in attempts to electricity. It consists of a fixed conductor to which a U-shaped wire bracket hangs freely can move like a pendulum. This unit tests can be performed that show the interaction between two current-carrying conductors.

Ampère showed that parallel electrical conductors attract each other when they are traversed by current and the current in the two conductors in the same direction flows and repel when the current flow is opposite. He suspected that a magnetic field around the current carrying conductor is formed.

In further experiments discovered amperes that is an electrical conductor, which is wound up into a coil, acts as a bar magnet. As voltage source he used a Volta element, a simple chemical battery.

Kelvinsche current balance

Lord Kelvin developed in 1882 a current balance new type. This consists of a beam balance, and on both beam ends ever is a coil. Two other immovable coils are mounted above the two moving coils. The four coils are connected in series so that each coil by the same current flows in such a way that the coils tighten on one side of the balance and push off on the other side. From the weight that is required to keep the balance in the balance, a function of the current strength, the force can be calculated between the coils and this makes it possible to calibrate the current levels in amperes.

Kelvinsche current scales were manufactured by White in Glasgow and exported by James W. Queen of Philadelphia in the United States, where they were in 1889 sold for $ 200 apiece.

Current balance in physics experiment

In physics class provides a current balance building a popular means for the experimental study of the magnetic flux density B represents an energized field coil generates a constant magnetic field, which is guided by a soft magnetic material. A U-shaped grab bar is placed in the magnetic field and through which a known (measured) stream. An electronic scale measures the power change from the non-energized state, in which only the weight force is applied. By changing the current flow and different length head strap to the connection points with the force of:

Hence the magnetic flux density determined by the following relationship: