What is :
(a) the highest
(b) the lowest total resistances that can be secured by combinations of four coils of resistances `4 Omega,8 Omega,12 Omega,24 Omega` ?

Options

A. `50 ohm, 4 ohm`
B. 48 ohm, 2 ohm
C. 48 ohm, 8 ohm
D. None of the above

Answer

B

Explanation

(a) The highest resistance is secured when all the four coils are connected in series. In that case,
`R_s = 4 Omega + 8 Omega + 12 Omega + 24 Omega = 48 Omega`
(b) The lowest resistance is secured when all the four coils are connected in parallel. In that case,
`(1)/(R_p) = (1)/(4)+(1)/(8)+(1)/(12)+(1)/(24) = (6+3+2+1)/(24) = (12)/(24)`, where `R_p = (24)/(12) Omega = 2 Omega`.