The variable capacitance of an old radio tuner consists of four plates connected

Question

The variable capacitance of an old radio tuner consists of four plates connected together placed alternately between four other plates, also connected together (see the figure).(Figure 1) Each plate is separated from its neighbor by 1.7 mm of air. One set of plates can move so that the area of overlap of each plate varies from 1.2 cm2 to 9.8 cm2 .

Part A

Are these seven capacitors connected in series or in parallel?

Part B

Determine the range of capacitance values.

Express your answers using two significant figures separated by a comma.

Explanation / Answer

A) these connected in parallel connection.

B) Ceq = C1 + C2 + C3 + C4 ........

this will be minimum when each capacitor is minimum.

C will be minimum when overlap area is minimum.

C = e0 A / d = (8.854 x 10^-12 x 1.2 x 10^-4 ) / (1.7 x 10^-3 )

C = 6.25 x 10^-13 F

Ceq _min = 7 x 6.25 x 10^-13 = 4.37 x 10^-12 F

Ceq will be maximum when each C will be max.

Cmax = (8.854 x 10^-12 x 9.8 x 10^-4) / (1.7 x 10^-3)

=5.10 x 10^-12 F

Ceq _max = 7 x Cmax = 3.572 x 10^-11 F

Range = from 6.25 x 10^-13 F to 357.2 x 10^-13 F

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