# Physics Questions and Answers – Electrostatic Potential due to an Electric Dipole

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Electrostatic Potential due to an Electric Dipole”.

1. Which one is the correct expression of electric potential on the axial point of a dipole whose dipole moment is p and length is 2l, at a distance of r?
a) $$\frac {p}{r^2}$$
b) $$\frac {p}{l^2}$$
c) $$\frac {p}{(r^2-l^2)}$$
d) $$\frac {p}{2lr}$$

Explanation: Electric potentials due to the two point charges of the dipole are $$\frac {q}{(r-l)}$$ and $$\frac {-q}{(r+l)}$$. Therefore, total potential = $$\frac {q}{(r-l)} – \frac {q}{(r+l)} = \frac {2ql}{(r^2-l^2)}$$. Now 2ql = dipole moment of the dipole=p. Therefore, the expression becomes $$\frac {p}{(r^2-l^2)}$$.

2. What is the electric potential at the perpendicular bisector of an electric dipole?
a) Positive
b) Negative
c) Zero
d) Depends on medium

Explanation: Any point on the perpendicular bisector is equidistant from both the charges of the dipole. Therefore, the electric potential at that point is equal and opposite due to the two different charges. Therefore, the total electric potential at that point is zero.

3. What is the correct diagram regarding the variation of an electric field with distance from an electric dipole if the distance is very large than the dipole length?
a)

b)

c)

d)

Explanation: If the distance of a point from the dipole is very small, we can simply neglect the l2 term compared to the r2 term in the potential expression V=$$\frac {p}{(r^2-l^2)}$$. Therefore, the expression becomes $$\frac {p}{r^2}$$.
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4. The electric potential at an axial point of a dipole is the maximum.
a) True
b) False

Explanation: Electric field at a distance r from a dipole and at an angle θ is p*$$\frac {\cos \theta}{r^2}$$, where p is the dipole moment of that dipole. If θ becomes 0 degrees, cosθ will be the maximum i.e. 1. Therefore, the electric field is the maximum at the axial points.

5. What is the dimension of the dipole moment?
a) [I L T]
b) [I L T-1]
c) [I L2 T]
d) [I T]

Explanation: Dipole moment = charge*length of the dipole. The electric charge has dimensions [I T] and length has dimensions [L]. Therefore, the dipole moment has the dimension [I T L] and has unit C*m of C*cm.

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