Explain briefly: a) Your buddy, studying with you, notices that in your notes yo

Question

Explain briefly: a) Your buddy, studying with you, notices that in your notes you mention an "example
where the net charge is zero but the electric field (of that same thing) is not zero." Your buddy says that's
clearly a mistake and is impossible. What's the simplest example of such a thing?
b) A +q and -q charge lie on the x-axis, separated by some short distance. Is there any point in the space
surrounding these two charges where the field is equal to zero? (Stay in the vicinity of the two.)
c) A +q and -4q charge lie on the x-axis, separated by some short distance. Is there any point in the space
surrounding these two charges where the field is equal to zero? (Stay in the vicinity of the two.)
d) How does the direction of the electric field of a dipole compare to the direction of the dipole moment
on the axis of the dipole? and, off-axis from the dipole?

Explanation / Answer

a)

The net charge is zero for a dipole ( two same magnitude opposite polarity of charges separated by a small distance) but the field due to this dipole is non zero.

b)

Yes, along the line joining the two charges, there are points where the net electric field results to zero. The field due to the postiive charge at a location would be equal to the field due to the negative charge but in opposite direction which results to zero net electric field.

c)

Same as part b. Yes possible.

d)

Along the axis:

The direction of the field due to the charges would be along the direction of the dipole moment towards the positive charge.

off-axis from the dipole

The direction of the field due to the charges would be along the direction of the dipole moment is normal to the plane and given by the right hand rule.

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