The timing device in an automobile's intermittent wiper system is based on an RC time constant and utilizes a 0.350 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 17.0 s?

Explanation:

Given that,

Capacitance of the capacitor is

C = 0.350 µF = 0.35 × 10^-6 F

Time constant ranges from

τ(min) = 2.5s

τ(max) = 17s

We want to find the range the resistance

Now, using the time constant formulae

τ = RC

Then, R= τ/C

So,

R(min) = τ(min) /C

R(min) = 2.5 / 0.35 × 10^-6

R(min) = 7.143 × 10^6 Ω

R(min) = 7.143 MΩ

R(max) = τ(max) /C

R(max) = 17 / 0.35 × 10^-6

R(max) = 48.57 × 10^6 Ω

R(max) = 48.57 MΩ

So the resistance ranges from

7.143 MΩ < R < 48.57 MΩ

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia