Ques. 1AIPMT 2007
Three point charges +q, -2q and + q are placed at points (x = 0, y = a, z = 0), (x = 0, y = 0, z = 0) and (x = a, y = 0, z = 0) respectively. The magnitude and direction of the electric dipole moment vector of this charge assembly are
- 2qa along the line joining points (x = 0, y = 0, z = 0) and (x = a, y = a, z = 0)
- qa along the line joining points (x = 0, y = 0, z = 0) and (x = a, y = a, z = 0)
- 2qa along +x direction
- 2qa along +y direction
Answer
(1) 2qa along the line joining points (x = 0, y = 0, z = 0) and (x = a, y = a, z = 0)
Solution
The -2q charge at the origin can be split into two charges -q and -q, which gives two dipoles:
(i) -q at origin and +q at (0, a, 0): p1 = qa j
(ii) -q at origin and +q at (a, 0, 0): p2 = qa i
Adding them, p = qa( i + j)
| p| = 2 qa
∴ The dipole moment is 2 qa, directed at 45 to the x-axis, i.e., along the line from (0, 0, 0) to (a, a, 0).
Answer: (1)