Two 3 cm wide magnets are placed on an electronic balance with opposite poles facing each other. A 1 Ω length of wire is connected to a battery with EMF 1.5 V and internal resistance 0.5 Ω. The wire is arranged so that it passes through the magnets perpendicular to the field between them.
If the reading on the balance goes down by 4g what is the flux density between the poles of the magnet?