Answer:
B=0.047mT
Explanation:
The magnetic field in this region is given by the followin equation[tex]F_g=F_b+F_e[/tex]
Where [tex]F_g = mg, F_b=qvB, F_e=qE[/tex]
Replacing all of this values,
m = 5.0 g, q = −70 μC, g= 9.8 m/s^2, E=700N/C
We have,
[tex]mg=qvB+qE\\(0.005)(9.8) = (-70*10^{-6})(30*10^3)(B)-(70*10^{-6})(700)\\B=0.047T\\B=0.047mT[/tex]