a uniform magnetic field equal to 4 T is in the +Z direction. find the force exrted by the field on a proton if the velocity of the proton is 7km/s in the i direction
F = q(v x B)
Where the bold terms are the usual vectors.
Here, B = 4T, v = 7000 m/s, q = +e
From the above formula,
F = qvBsinθ
But since the vectors are crossed, θ = 90, sinθ = 1
=> F = qvB
Put in the values of q, B, and v for the force.
As for the direction, it is given by the direction of the cross product of the velocity and field vectors, which in this case is in the negative Y direction.