Question

(4) charges are placed each at a distance `a` from origin . The dispole moment of configuration is .
.
A. ` 2qa hat j`
B. ` 3 q a hat j`
C. ` 2 a q [ hat I + hat j]`
D. none

Answer 1

Correct Answer - A

` | vec P_1 | = | vec P _3 | =q sqrt 2 a rArr |vec P_2| =2 P_1`
` vec P =vec P_1 +vec P_2 + vec P_3`
` P_x =P_1 cos 45^@ -2 P_1 cos 45^@ + P_1 cos 45^@`
` P_x =0`
` P_y =P_1 sin 45^@ + 2 P_1 sin 45^@ - P_1 sin 45^@`
` P_y = sqrt 2P_1`
` vec P =P_x i + P_y har j` `rArr vec P =2 qa hat j`.