Fundamentals of Physics

During an MRI (magnetic resonance imaging) scan, a patient is placed in an apparatus in which there is a large steady magnetic field and a small sinusoidally varying magnetic field. This medical procedure has been performed countless times without harm to patients. Indeed, a magnetic field should not be harmful. In a few cases, however, the patient has been burned during a scan because the operating staff made a simple error about the physics of the arrangement.

How can a magnetic field cause burns?

The answer is in this chapter.

30-1   What Is Physics?

In Chapter 29 we discussed the fact that a current produces a magnetic field. That fact came as a surprise to the scientists who discovered the effect. Perhaps even more surprising was the discovery of the reverse effect: A magnetic field can produce an electric field that can drive a current. This link between a magnetic field and the electric field it produces (induces) is now called Faraday’s law of induction.

The observations by Michael Faraday and other scientists that led to this law were at first just basic science, interesting in that they revealed another facet of how our universe works. Today, however, applications of that basic science are almost everywhere. For example, induction is the basis of the electric guitars that ...