Electrical Work and Energy
For charge Q crossing a constant potential difference V, work is QV. For time-varying conditions, energy is the integral of VI over time; kilowatt-hour is an energy unit.
Why this shows up in the exam
Battery work · Electricity consumption · Energy supplied to mixed systems
Learn the idea
Moving charge through a potential difference transfers electrical energy. A source gives each coulomb E joules of energy, while circuit elements convert that energy to heat, light, motion, or stored energy.
🧠 Memory hook: Volts are joules per coulomb.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- W = Q V — energy transfer for charge Q across constant V
- W = integral V(t) I(t) dt — general electrical energy transfer
- 1 kWh = 3.6 x 10⁶ J — commercial energy conversion
How to approach it
- 1Identify charge, current-time, or power-time data
- 2Choose QV or integrate VI
- 3Report joules or convert energy units
Common slip-ups that cost marks
- •Calling kWh a unit of power
- •Using W = QV when V varies without integration
- •Ignoring energy leaving as useful work
🌟 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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