Question

If electric field intensity at a certain distance from a dipole on its axis is E1 and at the same distance but on the perpendicular bisector of the dipole is E2, then __________

(a) E1=E2

(b) E1=2 E2

(c) E1=4 E2

(d) E1=3 E2

The question was posed to me in a national level competition.

Enquiry is from Electric Dipole in chapter Charges and Fields of Physics – Class 12

Answer 1

Correct choice is (b) E1=2 E2

Explanation: If the dipole moment of a dipole is p, then electric field intensity at a distance r from the dipole on its axis will be \(\frac {2p}{r^3}\). But electric field intensity at a distance r from the dipole on its perpendicular bisector is \(\frac {p}{r^3}\). Both the formulas are derived by assuming r >> length of the dipole. Thus E1=\(\frac {2p}{r^3}\) and E2=\(\frac {p}{r^3}\) and hence E1=2 E2.