Question

An electric iron rated 2.2 kW, 220 V is operated at 110 V supply. Find:

1. its resistance, and
2. heat produced by it in 10 minutes.

Answer 1

Given: P = 2.2 kW = 2200 W, 

V = 220 V 

i. Power (P) = `V^2/R`

⇒ R = `V^2/P`

= `220^2/2200`

= `48400/2200` 

= 22 Ω

New power consumed operated at 110 V:

P' = `V^2/R`

= `110^2/22`

= `12100/22`

= 550 W

ii. Heat produced (H) = Pt

Heat produced in 10 minutes:

H = P' × t

= 550 × 10 min

= 550 × 600 s

= 330000 J

= 3.3 × 10⁵ J