Electric Dipole Moment
For charges -q and +q separated by vector d from negative to positive, p = qd. The ideal-dipole approximation requires observation distance much larger than |d|.
Why this shows up in the exam
Building a dipole from two charges · Converting units to C m · Comparing dipole strengths
Learn the idea
A dipole's moment points from negative to positive charge and equals charge times separation. At distances much larger than its separation, a neutral pair is summarized by one vector p that records both orientation and strength.
🧠 Memory hook: Dipole moment points minus to plus.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- p = q d — dipole moment vector from -q to +q
- |p| = q d — magnitude for equal opposite charges
How to approach it
- 1Mark -q and +q
- 2Draw d from negative to positive
- 3Check the far-field condition before idealizing
Common slip-ups that cost marks
- •Pointing p from positive to negative
- •Using half-separation instead of full separation
- •Applying ideal-dipole formulas too close to the charges
🌟 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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