A charge `+2q` moves vertically upwards with speed `v`, a second charge `-q` moves horizontally to the right with the same speed `v`, and a third charge `+q` moves horizonatlly to the right with the same speed `v`. The point `P` is located a perpendicular distance a away from each charge as shown in the figure. The magnetic field at point `P` is

Options

A. Into the page with magnitude `(mu_(0))/(4pi)(2qv)/(a^(2))`
B. Into the page with magnitude `(mu_(0))/(4pi)(4qv)/(a^(2))`
C. out of the page with magnitude `(mu_(0))/(4pi)(2qv)/(a^(2))`
D. out of the page with magnitude `(mu_(0))/(4pi)(4qv)/(a^(2))`

Answer

D

Explanation

`vecB_(p)=vecB_(q)+vecB_(2q)+vecB_(-q)`
`(mu_(0))/(4pi)(qv)/(a^(2))odot+(mu_(0))/(4pi)(2qv)/(a^(2))odot+(mu_(0))/(4pi)(qv)/(a^(2))odot=(mu_(0))/(4pi)(4qv)/(a^(2))odot`