# Electromagnetic Theory Questions and Answers – Electric Potential

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This set of Electromagnetic Theory Multiple Choice Questions & Answers (MCQs) focuses on “Electric Potential”.

1. Potential difference is the work done in moving a unit positive charge from one point to another in an electric field. State True/False.
a) True
b) False

Explanation: The electric potential is the ratio of work done to the charge. Also it is the work done in moving a unit positive charge from infinity to a point in an electric field.

2. A point charge 2nC is located at origin. What is the potential at (1,0,0)?
a) 12
b) 14
c) 16
d) 18

Explanation: V = Q/(4πεr), where r = 1m
V = (2 X 10-9)/(4πε x 1) = 18 volts.

3. Six equal point charges Q = 10nC are located at 2,3,4,5,6,7m. Find the potential at origin.
a) 140.35
b) 141.35
c) 142.35
d) 143.35

Explanation: V = (1/4πεo) ∑Q/r = (10 X 10-9/4πεo)
(0.5 + 0.33 + 0.25 + 0.2 + 0.166 + 0.142) = 143.35 volts.

4. A point charge 0.4nC is located at (2, 3, 3). Find the potential differences between (2, 3, 3)m and (-2, 3, 3)m due to the charge.
a) 2.5
b) 2.6
c) 2.7
d) 2.8

Explanation: Vab = (Q/4πεo)(1/rA) + (1/rB), where rA and rB are position vectors rA = 1m and rB = 4m. Thus Vab = 2.7 volts.

5. Find the potential of V = 60sin θ/r2 at P(3,60,25)
a) 5.774
b) 6.774
c) 7.774
d) 8.774

Explanation: V = 60sin θ/r2, put r = 3m, θ = 60 and φ = 25, V = 60 sin 60/32 = 5.774 volts.

6. Given E = 40xyi + 20x2j + 2k. Calculate the potential between two points (1,-1,0) and (2,1,3).
a) 105
b) 106
c) 107
d) 108

Explanation: V = -∫ E.dl = -∫ (40xy dx + 20x2 dy + 2 dz), from (2,1,3) to (1,-1,0), we get Vpq on integrating from Q to P. Vpq = 106 volts.

7. The potential difference in an open circuit is
a) Zero
b) Unity
c) Infinity
d) Circuit does not exist open

Explanation: In an open circuit no current exists due to non-existence of loops. Also voltage/potential will be infinity in an open circuit.

8. The potential taken between two points across a resistor will be
a) Positive
b) Negative
c) Zero
d) Infinity

Explanation: The resistor will absorb power and dissipate it in the form of heat energy. The potential between two points across a resistor will be negative.

9. What is the potential difference between 10sinθcosφ/r2 at A(1,30,20) and B(4,90,60)?
a) 2.386
b) 3.386
c) 4.386
d) 5.386

Explanation: Potential at A, Va = 10sin30cos20/12 = 4.6985 and Potential at B, Vb = 10sin90cos60/42 = 0.3125. Potential difference between A and B is, Vab = 4.6985 – 0.3125 = 4.386 volts.

10. The voltage at any point in an ac circuit will be
a) Peak voltage
b) RMS voltage
c) Average voltage
d) Source voltage

Explanation: In any ac circuit, the voltage measured will not be exact maximum. In order to normalise, we assume the instantaneous voltage at any point be 70.7% of the peak value, which is called the root mean square (RMS)voltage.

Sanfoundry Global Education & Learning Series – Electromagnetic Theory.
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