At a particular moment, the current in the primary coil is clockwise, as viewed from the secondary coil. At the center of the secondary coil, the field from the primary coil is

A. To the right.

B. To the left.

C. Zero.

Your laptop has wireless communications connectivity, and you might even have a wireless keyboard or mouse. But there's one wire you haven't been able to get rid of yet-the power cord.

Researchers are working on ways to circumvent the need for a direct electrical connection for power, and they are experiencing some success. Recently, investigators were able to use current flowing through a primary coil to power a \(60 \mathrm{~W}\) lightbulb connected to a secondary coil \(2.0 \mathrm{~m}\) away, with approximately \(15 \%\) efficiency. The coils were large and the efficiency low, but it's a start.

The wireless power transfer system is outlined in Figure VI.2. An AC supply generates a current through the primary coil, creating a varying magnetic field. This field induces a current in the secondary coil, which is connected to a resistance (the lightbulb) and a capacitor that sets the resonance frequency of the secondary circuit to match the frequency of the primary circuit.

Transcribed Image Text:

FIGURE VI.2 Primary coil Secondary coil www R C