D.4 Induction

How is magnetic flux defined in words?

Magnetic flux equals the magnetic flux density times the area of the surface times the cosine of the angle between the field and the normal to the surface.

What does Faraday’s Law of Induction state?

The magnitude of the induced electromotive force (emf) is directly proportional to the rate of change of magnetic flux linkage.

What is the formula for the emf induced in a straight conductor moving through a magnetic field?

Induced emf equals magnetic flux density times the velocity of the conductor times the length of the conductor.

What is Lenz’s Law regarding the direction of induced emf?

The direction of the induced emf is such that it creates a magnetic field that opposes the change in magnetic flux that produced it.

Why is Lenz’s Law considered a consequence of the conservation of energy?

If the induced field supported the change, energy would be created from nothing; instead, work must be done against the opposing force to induce the current.

What type of emf is produced when a coil rotates at a constant speed within a uniform magnetic field?

The rotation produces a sinusoidally varying (alternating) electromotive force.

How does increasing the frequency of rotation affect the induced emf in a generator?

Increasing the frequency increases both the maximum (peak) emf and the frequency of the alternating current.

What are the three main ways to induce an emf in a system?

By using a time-varying magnetic field, by rotating a coil in a magnetic field, or by creating relative motion between a conductor and a field.

What is the Faraday's Law formula including the number of turns in a coil?

Emf equals negative the number of turns times the change in magnetic flux divided by the change in time.

What is self-induction qualitatively?

It is the process where a changing current in a circuit induces an electromotive force in the same circuit that opposes the change in current.

In a graph of magnetic flux versus time, what does the gradient represent?

The gradient of the graph represents the magnitude of the induced electromotive force at that instant.