Question

The timing device in an automobile's intermittent wiper system is based on an RC time constant and utilizes a 0.520 µF capacitor and a variable resistor. Over what range (in MΩ) must R be made to vary to achieve time constants from 2.50 to 19.0 s?

Answer 1

Range of R is from 4.81MΩ to 36.54 MΩ

Step-by-step explanation:

Capacitance(C) = 0.520 µF = 0.52 x 10^(-6) F

Time constant = from 2.5 to 19 seconds

In RC circuits, time constant is;

r = RC

Where R is the range (in MΩ)

And r is time constant

Thus,

R = r/c

So minimum range will be at 2.5seconds.

Thus; Rmin = 2.5/(0.52 x 10^(-6)) = 4.81 x 10^(6) Ω = 4.81MΩ

Rmax = 19/(0.52 x 10^(-6)) = 36.54 x 10^(6) Ω = 36.54 MΩ