A generator with a single loop produces the greatest magnetic force on the charges and the greatest induced emf when

a.
the plane of the loop is parallel to the magnetic field.
b.
half of the loop segments are moving perpendicular to the magnetic field.
c.
the plane of the loop is perpendicular to the magnetic field.
d.
none of the above

a. The wires are cutting the maximum concentration of magnetic field lines.

The correct answer is c. the plane of the loop is perpendicular to the magnetic field.

To understand why, we need to consider the concept of magnetic flux. Magnetic flux is a measure of the number of magnetic field lines passing through a given area. When a loop of wire is placed in a magnetic field, the magnetic field lines passing through the loop change with time, causing an induced emf (electromotive force) and generating a current.

The magnitude of the induced emf and the force experienced by the charges in the loop depend on the rate of change of magnetic flux through the loop. According to Faraday's Law of electromagnetic induction, the induced emf is directly proportional to the rate of change of magnetic flux.

When the plane of the loop is parallel to the magnetic field (option a), the number of magnetic field lines passing through the loop remains constant. As a result, there is no change in magnetic flux, leading to no induced emf or magnetic force.

When half of the loop segments are moving perpendicular to the magnetic field (option b), the magnetic flux through the loop changes as the moving segments cross the magnetic field. However, since only half of the loop is moving, the overall change in magnetic flux is reduced compared to the case where the entire loop is perpendicular to the magnetic field. As a result, the induced emf and magnetic force are also reduced.

Only when the plane of the loop is perpendicular to the magnetic field (option c), the maximum number of magnetic field lines pass through the loop, resulting in the highest rate of change of magnetic flux. This leads to the greatest induced emf and magnetic force.

Therefore, the correct option is c. the plane of the loop is perpendicular to the magnetic field.