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) \(\frac {p}{2lr}\)
View Answer

Answer: c
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 \(\frac {p}{(r^2-l^2)}\).
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2. What is the electric potential at the perpendicular bisector of an electric dipole?
a) Positive
b) Negative
c) Zero
d) Depends on medium
View Answer

Answer: c
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)

View Answer

Answer: a
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
View Answer

Answer: a
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]
View Answer

Answer: a
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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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn | Youtube | Instagram | Facebook | Twitter