Question

A system has two charges q_A = 2.5 × 10⁻⁷ C and q_B = −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?

Answer 1

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 = q_A + q_B = 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
= q_A × d = q_B × 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.