The power supply drives the primary coil at \(9.9 \mathrm{MHz}\). If this frequency is doubled, how must the capacitor in the secondary circuit be changed?

A. Increase by a factor of 2 

B. Increase by a factor of \(\sqrt{2}\)

C. Decrease by a factor of 2 

D. Decrease by a factor of 4 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