Electrical Heating with Calorimetry
With efficiency eta, eta Pt equals mc Delta T plus mL for the included thermal stages. For an insulated thermodynamic system receiving heat and doing work, apply the first law with a declared sign convention.
Why this shows up in the exam
Electric kettles · Melting ice by resistance heating · Heating gases and internal-energy accounting
Learn the idea
Electrical energy becomes sensible heat, latent heat, or internal-energy change according to the thermal process. A heater's VI t energy must pay every thermal energy requirement: raising temperature, changing phase, and any stated losses or useful work.
🧠 Memory hook: Electrical energy pays each thermal bill in sequence.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- eta P t = m c Delta T + m L — heating plus phase change with efficiency eta
- Delta U = Q - W_by — first law using work done by the system
- P = I² R — resistive heater power if I and R are known
How to approach it
- 1List all thermal stages
- 2Set supplied electrical energy equal to required energy with efficiency
- 3Solve time and check units
Common slip-ups that cost marks
- •Omitting latent heat
- •Using Celsius instead of Delta T incorrectly
- •Mixing power and energy
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A cell of emf 6 V and internal resistance 1 ohm is connected to a 2 ohm resistor. Find the circuit current.
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