Work-Energy in an Electric Field
For electrostatic fields, W_field = -Delta U = q(V_i-V_f) and Delta K = W_field when no other force does work.
Why this shows up in the exam
Speed after moving through a field · Work between charged sheets · Released-charge energy changes
Learn the idea
Electric work changes kinetic energy and depends on the potential difference, not the path. Instead of tracking time, compare electric potential energy at the endpoints. In a uniform field, only displacement along the field contributes.
🧠 Memory hook: Field work is minus potential-energy change.
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_i - V_f) — work done by the electric field
- Delta K = W_net — work-energy theorem
- Delta V = -E dot Delta r — uniform-field potential change
How to approach it
- 1Choose initial and final points
- 2Compute Delta V or electric work
- 3Include all work before solving for speed
Common slip-ups that cost marks
- •Using path length instead of displacement projection
- •Dropping the sign of q
- •Equating electric work to Delta K when other forces also 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.
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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