If two resistors of value r are connected in series and then in parallel, what is the difference in equivalent resistance in both cases?
a) 0 b) 3R/2 c)R/2 d)2/R

b) 3R/2

Explanation:

When in series, the equivalent resistance is:

R = r + r

R = 2r

When in parallel, the equivalent resistance is:

R = (1/r + 1/r)⁻¹

R = (2/r)⁻¹

R = r/2

The difference is:

ΔR = 2r − r/2

ΔR = 3r/2