What is the expression for the calculation of magnetic flux density using a current balance.

This diagram shows a fixed horizontal wire passing centrally between the poles of a permanent magnet that is placed on a top-pan balance.

With no current flowing, the balance records a mass of $102.45g.$ When a current of $4.0 g.$ flows in the wire, the balance records a mass of $101.06 g.$

(c) The length of the wire in the magnetic field is $5.0 cm$ Calculate the average magnetic flux density between the poles of the magnet.

A current-carrying conductor placed at right angles to a uniform magnetic field experiences a force of$4.70\times {10}^{-3}N.$ Determine the force on the wire when, separately:

(b) the magne tic flux density is halved

A copper wire carrying a current of$1.2A$ has $3.0cm$ of its length placed in a uniform magnetic field, as shown.

The force experienced by the wire is $3.8\times {10}^{-3}N$ when the angle between the wire and the magnetic field is$50°.$

(a) Calculate the magnetic flux density.

This diagram shows a current-carrying wire frame placed between a pair of Magnadur magnets on a yoke. A pointer is attached to the wire.

A current of $8.5 A$8.5 A in the wire causes the pointer to move vertically upwards. A small paper tape is attached to the pointer and the current is adjusted until the weight of the paper tape causes the pointer to return to its initial position (with no current and no paper tape). The mass of the paper tape is $60 mg.$ The section of the wire between the poles of the magnetic has a length of $5.2cm$.

(c) Calculate the magnetic flux density of the magnetic field between
the poles of the magnet.

A wire of length$50 cm$  carrying a current lies at right angles to a magnetic field of flux density$5.0mT.$

(a) If${10}^{18}$electrons pass a point in the wire each second, what current is flowing? (electron chargee $=1.60\times 10-19 C.$)