Define the term magnetic flux density.
An insulated rectangular coil of wire, made up of $40$ turns, is hung in a cradle from a newton meter, as shown in Fig. 7.1. The vertical sides of the coil measure $5.00\,\text{cm}$ and the horizontal sides measure $3.00\,\text{cm}$. The newton meter initially reads $0.563\,\text{N}$. A U-shaped magnet is placed on a top-pan balance, which has been zeroed to $0.00\,\text{g}$. The lower edge of the coil is then lowered into the space between the poles of the U-shaped magnet, as shown in the side view in Fig. 7.2.
Explain why the current produces a vertical force on the coil.
Determine the flux density $B$ of the uniform magnetic field, giving your answer to three significant figures.
Determine the new reading on the newton meter. Explain your answer.