Many computer keyboards operate on the principle of capacitance. As shown in Figure 20-18, each key forms a small parallel-plate capacitor whose separation is reduced when the key is depressed.

Figure 20-18,

(a) Does depressing a key increase or decrease its capacitance? Explain.
(b) Suppose the plates for each key have an area of 47.5 mm2 and an initial separation of 0.550 mm. In addition, let the dielectric have a dielectric constant of 3.75. If the circuitry of the computer can detect a change in capacitance of 0.425 pF, what is the minimum distance a key must be depressed to be detected?

Transcribed Image Text:

Pushing the key... moves the plates closer together. Plates Dielectric