Question

An electric kettle takes 4 A current at 220 V. If the entire electric energy is converted into heat energy, then the time (in minutes) taken to increase the temperature of 1 kg of water from 34 °C to 100 °C is

• A. 7.50
• B. 4.50
• C. 5.25
• D. 6.25

Hint:

Use energy conservation and power formulas to calculate heating time for electric appliances.

Answer 1

The Correct Option is C

Step 1: Calculate energy required to heat water
Energy needed to raise temperature: \[ Q = m c \Delta T, \] where, \(m = 1\, \mathrm{kg}\), \(c = 4200\, \mathrm{J/kg^\circ C}\) (specific heat of water), \(\Delta T = 100 - 34 = 66^\circ C.\)
So, \[ Q = 1 \times 4200 \times 66 = 277200\, \mathrm{J}. \] Step 2: Calculate power input
Power \(P = VI = 220 \times 4 = 880\, \mathrm{W}\) (watts = joules/second).
Step 3: Calculate time
Time \(t = \frac{Q}{P} = \frac{277200}{880} = 315\, \mathrm{seconds}.\)
Convert to minutes: \[ t = \frac{315}{60} = 5.25 \, \mathrm{minutes}. \] Step 4: Conclusion
The time taken to heat the water is 5.25 minutes.