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, q_A = 2.5 × 10⁻⁷C

At B, amount of charge, q_B = −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.