A type of touchscreen called \"capacitive touchscreen\" consists of an insulator

Question

A type of touchscreen called "capacitive touchscreen" consists of an insulator such as glass, coated with a transparent conductor such as indium tin oxide. As the human body is also an electrical conductor, touching the surface of the screen results in a distortion of the screen's electrostatic field, measurable as a change in capacitance.

A touchscreen capacitor is maintained at a constant potential difference of 4.5 Volts. When the screen is touched the capacitance changes from 9.3 nF to 5.9 nF.

How much charge flows through the circuit?

Make sure to get the correct sign: it should be positive if the charge leaves the capacitor, and negative if the charge flows into the capacitor.

Explanation / Answer

We know,
Q = C * V
C = Q/V

As capacitor is maintained at a constant potential difference of 4.5 Volts, Value of Capacitance is directly proportional to Charge.

As the capacitance changes from 9.3 nF to 5.9 nF, Charge leaves the capacitor -

Qinitial = 9.3 nF * 4.5
Qfinal = 5.9 nF * 4.5

Charge flows through the circut = Qinitial - Qfinal
Charge flows through the circut = (9.3 - 5.9) nF * 4.5 v
Charge flows through the circut = + 15.3 nC

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