Question

Calculate the current flowing through a nichrome wire, immersed in 100 g of oil at 20°C, such that the final temperature of the oil rises to 80°C in five minutes, when the supply of e.m.f. is 10 V. [Sp. heat capacity of oil is 0.85 Jg⁻¹°C⁻¹]

Answer 1

I = ?; p.d. = 10 V; t = 5 min = 300 s

m = 100 g; S.H.C. = 0.85 Jg⁻¹°C⁻¹; θ_R = (80 − 20)°C = 60°C

Energy produced in wire = I × V × t

= I × 10 × 300 Vs

Energy absorbed by oil = m c θ_R

= 100 × 0.85 × 60 J

∴ By the law of conservation of energy

I × 10 × 300 = 100 × 0.85 × 60

\[\text{I} =\frac{100 \times 0.85 \times 60}{10 \times 300}\]

= 1.7 A