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Question
A system has two charges qA = 2.5 × 10−7 C and qB = −2.5 × 10−7 C located at points A: (0, 0, − 15 cm) and B: (0, 0, + 15 cm), respectively. What are the total charge and electric dipole moment of the system?
Solution
Both the charges can be located in a coordinate frame of reference as shown in the given figure.
At A, amount of charge, qA = 2.5 × 10−7C
At B, amount of charge, qB = −2.5 × 10−7 C
Total charge of the system,
q = qA + qB
= 2.5 × 107 C − 2.5 × 10−7 C
= 0
Distance between two charges at points A and B,
d = 15 + 15 = 30 cm = 0.3 m
Electric dipole moment of the system is given by,
p = qA × d = qB × d
= 2.5 × 10−7 × 0.3
= 7.5 × 10−8 C m along positive z-axis
Therefore, the electric dipole moment of the system is 7.5 × 10−8 C m along positive z−axis.
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