Question

magnetic flux is directly proportional to area while magnetic flux density is inversely proportional to area??? ​

Answer 1

Faraday’s law of induction states that an electromotive force is induced by a change in the magnetic flux.

Key Points

• It is a change in the magnetic field flux that results in an electromotive force (or voltage).
• The magnetic flux (often denoted Φ or ΦB) through a surface is the component of the magnetic field passing through that surface.
• In the most general form, magnetic flux is defined as ΦB=∬AB⋅dA. It is the integral (sum) of all of the magnetic field passing through infinitesimal area elements dA.

Key Terms

• Vector area: A vector whose magnitude is the area under consideration, and whose direction is perpendicular to the surface area.
• Galvanometer: An analog measuring device, denoted by G, that measures current flow using a needle deflection caused by a magnetic field force acting upon a current-carrying wire.

The apparatus used by Faraday to demonstrate that magnetic fields can create currents is illustrated in the following figure. When the switch is closed, a magnetic field is produced in the coil on the top part of the iron ring and transmitted (or guided) to the coil on the bottom part of the ring. The galvanometer is used to detect any current induced in a separate coil on the bottom.

It was found that each time the switch is closed, the galvanometer detects a current in one direction in the coil on the bottom. Each time the switch is opened, the galvanometer detects a current in the opposite direction. Interestingly, if the switch remains closed or open for any length of time, there is no current through the galvanometer. Closing and opening the switch induces the current. It is the change in magnetic field that creates the current. More basic than the current that flows is the electromotive force (EMF) that causes it. The current is a result of an EMF induced by a changing magnetic field, whether or not there is a path for current to flow.