Question

Compare the formula ∆V=ε∆d and ∆V=(kq/r1) – {kq/r2). Explain the meaning of each symbol and

under what conditions can each formula be used.

Answer 1

The meaning of each symbol:

ε (but it should be E) - magnitude of electric field

∆d - distance between two points

$k=1/(4\pi\epsilon_0)$ - a constant

q - electric charge

r1, r2 - distance from the origin to the given point

The first equation ∆V=E∆d helps to determine the voltage drop between two points ∆d meters apart along a uniform electric field of magnitude E.

The second equation ∆V=(kq/r1) – {kq/r2) helps to determine the potential difference (or voltage drop) between two points distance r1 and r2 respectively from a charge q. We know that the field from the charge fades with distance. Therefore, the last equation is applicable for charges, the first one is applicable for uniform fields (like in capacitors or between two large charged sheets).