In this picture an ammeter is connected in the circuit of a conducting loop.  When the bar magnet is moved closer to, or farther from, the loop, an electromotive force (emf) is induced in the loop.  The ammeter indicates currents in different directions depending on the relative motion of magnet and loop.  Notice that, when the magnet stops moving, the current returns to zero as indicated by the ammeter.

Q:     A current loop is placed in a uniform magnetic field.  What orientation of the loop makes the magnetic flux maximum?  What orientations make the magnetic flux minimum?

A:    The concept of the flux is defined as the "amount of lines of field" traversing a surface.   Therefore, the maximum "amount of lines of field" passes through a surface when the surface is perpendicular to the lines of field, and the "amount of lines of field" passing through a surface is minimum (equal to zero) when the surface is parallel to the lines of field.  A convenient mathematical representation of this conceptual definition of flux is given by expressing flux as the dot (scalar) product between field and surface (both considered as vectors): _B = B ^. dA.  The magnitude of this scalar product is _B = BA cos .  When = 0 (meaning that the area is perpendicular to the field), cos = 1 and the flux has its maximum value.   When = 90° (meaning that the area is parallel to the field), cos = 0 and the flux has its minimum (zero) value.   Remember that an area can be considered a vector with magnitude equal the magnitude of the area and the direction in the normal of the area.

Q:     Will dropping a magnet down a long tube of conducting material cause a current in the tube?

A:    According to Faraday-Lenz law of electromagnetic induction, a current is generated in a closed conducting path (in this case the wall of the tube) if the cross-sectional area defined by the tube is traversed by a variable magnetic flux.  The magnet creates a dipole-like magnetic field that will pass through the cross-sectional area of the cylinder, thus defining a magnetic flux.  This flux varies in time only when the magnet approaches entrance and enters into the tube, and also when it approaches the exit and exits from the tube.  Only during these transient periods of time a current will be induced in the tube.  During the time when the magnet travels through the interior of the tube (as assuming that the tube is very long and the magnet is very far from both of the tubes ends) the magnetic flux remains constant and therefore no current will be induced in the tube.

Q:     What is the purpose of putting an inductor in a circuit?

A:    Presence of an inductor in an electric circuit has the effect of slowing down the increase of the current when the circuit is being closed, and slowing down its decrease when the circuit is being opened.  The behavior of such a circuit is characterized by the "time constant" ( = L/R ) of the circuit.  The larger the inductance, the larger the time constant.

Inductances in circuits maybe purposely inserted or parasitic.  The purposely inserted inductors are most often used in oscillating circuits used e.g. in radio emission or radio transmission applications.