How long will it take to heat 4 kg of water from 30ºC to 65ºC using an electric kettle taking 5 A from a 240 V…

Analyze the question: We need the time for an electric kettle to supply enough heat energy to raise the temperature of 4 kg of water from 30°C to 65°C.

Concept:

• Heat needed: Q = mcΔθ
• Electrical energy supplied: E = IVt
• Assuming no heat loss, IVt = mcΔθ

Solution:

1. Temperature change: Δθ = 65 − 30 = 35 K

2. Heat required: Q = 4 × 4200 × 35 = 588,000 J

3. Power of the kettle: P = IV = 5 × 240 = 1200 W

4. Time: t = Q / P = 588,000 / 1200 = 490 s

Answer: The time is 490 s, which is option C.

Tip: For heating questions with electrical appliances, always equate the two energy formulas: IVt = mcΔθ. Compute the power (IV) first, then divide the heat needed by it. Also, check that Δθ is the difference in temperatures, not either temperature itself.