What magnitude electric field is necessary to exactly balance this magnetic force?

A. \(1.8 \times 10^{-4} \mathrm{~N} / \mathrm{C}\)

B. \(1.5 \times 10^{-4} \mathrm{~N} / \mathrm{C}\)

C. \(1.0 \times 10^{-4} \mathrm{~N} / \mathrm{C}\)

D. \(0.9 \times 10^{-4} \mathrm{~N} / \mathrm{C}\)

The ocean is salty because it contains many dissolved ions. As these charged particles move with the water in strong ocean currents, they feel a force from the earth's magnetic field. Positive and negative charges are separated until an electric field develops that balances this magnetic force. This field produces measurable potential differences that can be monitored by ocean researchers.
The Gulf Stream moves northward off the east coast of the United States at a speed of up to \(3.5 \mathrm{~m} / \mathrm{s}\). Assume that the current flows at this maximum speed and that the earth's field is \(50 \mu \mathrm{T}\) tipped \(60^{\circ}\) below horizontal.