Potential Difference and Conservative Work
For a time-independent electrostatic field, the work done by the field from A to B equals q(V_A-V_B); external quasistatic work is the opposite, with no kinetic-energy change.
Why this shows up in the exam
path-independence questions · work on equipotential paths · sign of external versus field work
Learn the idea
Potential difference measures electrostatic work per unit charge, independent of path. Think of electric potential as electrical height: a charge moving between two levels changes energy, while the route between the levels does not matter in electrostatics.
🧠 Memory hook: Field work falls with potential; external work raises it.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- W_field = q(V_A - V_B) — electrostatic field; q is the moved test charge
- Delta U = q(V_B - V_A) — potential energy change between fixed endpoints
How to approach it
- 1Mark initial and final points
- 2Compute Delta V before multiplying by q
- 3State whose work is requested
Common slip-ups that cost marks
- •Using distance traveled instead of endpoint potentials
- •Confusing work by field with work by an external agent
- •Dropping the sign of the moved charge
🌟 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.
Two point charges 1 microC and 2 microC are 1 m apart in vacuum. Take k = 9 x 10^9 SI. Find the force magnitude.
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