CBSE Class 10 Answered

Given that,

Ratio of area of cross-section = 3:1

Resistance of thick wire, R₁ = 12 Ω

(a)

Now,

The resistance of a wire is inversely proportional to its cross-sectional area.

i.e., 

Thus,

Resistance of the thinner wire, R₂ = 3 × R₁ = 3× 12 = 36 Ω

(b)

(i) When two wires are connected in series, their equivalent resistance will be

R_eq = 12 Ω + 36 Ω = 48 Ω

(ii) When two wires are connected in parallel, their equivalent resistance will be

1/Req = 1/R₁ + 1/R₂

i.e., 1/(1/12 + 1/36) = 9 Ω.

(c)

The heat produced in a wire is inversely proportional to the resistance of the wire.