Answer:
Step-by-step explanation:
The force on a moving charge in a magnetic field acts in a direction perpendicular to the plane containing the magnetic field and the velocity of propagation of charge.
If charge flows in the direction of magnetic field , or opposite to magnetic field ,no force will act on the charge . Here no force is acting on the moving charge , therefore magnetic field must be along or against the direction of velocity of proton. Hence , magnetic field must be along or againt positive x direction.
b = B i or - Bi
if the proton moves along positive y direction , its velocity can be represented by the formula
v = 8.7 x 10⁵ j
Direction of force positive z direction so
F = 2.1 x 10⁻¹³ k
F = q ( v x b )
2.1 x 10⁻¹³ k = 1.6 x 10⁻¹⁹ x (8.7 x 10⁵ j x B i )
2.1 x 10⁻¹³ k = - 13.92 x 10⁻¹⁴k B
It is not matching so B is not along positive x direction . If it is in - x direction
b = - Bi
F = q ( v x b )
2.1 x 10⁻¹³ k = 1.6 x 10⁻¹⁹ x (8.7 x 10⁵ j x - B i )
2.1 x 10⁻¹³ k = 13.92 x 10⁻¹⁴k B
B = 1.5 T in negative x direction