A small immersion heater can be used in a car to heat a cup of water for coffee

Question

A small immersion heater can be used in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of water from 25degreeC to 95degreeC in 7.5 min. Assume the manufacturer's claim of 87 % efficiency. The specific heat of water is 4186 J/(kg middotdegree C). Approximately how much current does it draw from the car's 12-V battery? Express your answer to two significant figures and include the appropriate units. What is its resistance? Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

heat capacity of water: 4186 J / kg C
mass water = 0.12 kg

To heat water:
Q = 0.12*4186*(95-25) = 35162.4 J

Power = Q /(7.5*60) = 78.1386 J/s
Pbat = 78.1386/0.87 = 89.814 J/s

Pbat = v^2/r
r = 144/89.814 = 1.603 ohms
i = v/r = 12/1.603 = 7.486 A

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.