Question

The resistance of the series combination of two resistances is , when they are joined in parallel the total resistance is P If = n P, then the minimum possible value of n is....

(A) 4

(B) 3

(C) 2

(D) 1

Answer 1

The correct option (A) 4

Explanation:

For series connection, R1 + R2 = *

For parallels connection {(R1 ∙ R2)/(R1 + R2)} = p

given * = n P

∴ R1 + R2 = n ∙ [{R1 R2}/{R1 + R2}]

∴ Rxad12 + R22 + 2R1 R2 = nR1 R2

∴ (R1 – R2)2 + 4R1 R2 = nR1 R2

∴ (R1 – R2)2 – (n – 4)R1 R2 = 0

it R1 = R2 then

n – 4 = 0

n = 4

∴ minimum value = 4