Answer:
Magnetic field, 0.046 T
Step-by-step explanation:
Given that,
Mass of the charged particle, m = 5 g
Charge,

Electric field, E = 700 N/C
Speed of the charge particle, v = 30 km/s = 30000 m/s
To find,
The magnitude of the magnetic field in this region.
Solution,
The charged particle is moving horizontally with a constant speed, the gravitational force is balanced by the magnetic force and the electric force.



B = 0.046 T
Therefore, the magnitude of the magnetic field in this region is 0.046 T. Hence, this is the required solution.