Question

Calculate the current flowing through an electric drill, connected to a 200 V supply, if it drills a hole in a metal plate of mass 500 g, such that its temperature rises from 10°C to 60°C in 5 minutes, assuming all the work done is converted into heat energy. [S.H.C. of metal 0.6 Jg⁻¹°C⁻¹]

Answer 1

p.d. = 200 V; t = 5 min = 300 s; I = ?

m = 500 g; S.H.C. of metal 0.6 Jg⁻¹°C⁻¹; θ_R = (60 − 10)°C = 50°C

Energy produced in the drill = I × V × t

= I × 200 × 300 J

Energy absorbed by metal = m c θ_R

= 500 × 0.6 × 50 J

∴ By the law of conservation of energy

I × 200 × 300 = 500 × 0.6 × 50

\[\Rightarrow I = \frac{500 \times 0.6 \times 50}{200 \times 300}\]

\[\Rightarrow I = \frac{15000}{60000}\]

\[\therefore I = 0.25\text{A}\]