To solve this problem we will apply the concepts related to the Magnetic Force, this is given by the product between the current, the body length, the magnetic field and the angle between the force and the magnetic field, mathematically that is,

Here,
I = Current
L = Length
B = Magnetic Field
= Angle between Force and Magnetic Field
But 

Rearranging to find the Magnetic Field,

Here the force per unit length,

Replacing with our values,


Therefore the magnitude of the magnetic field in the region through which the current passes is 0.0078T
The amount of water needed is 287 kg
Explanation:
The amount of energy that we need to produce with the power plant is

We also know that the power plant is only 30% efficient, so the energy produced in input must be:

The amount of water that is needed to produce this energy can be found using the equation

where:
m is the amount of water
is the specific heat capacity of water
is the increase in temperature
And solving for m, we find:

Learn more about specific heat capacity:
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