일반물리학 2 — Current and Resistance: Problem 24

24 Swimming during a storm. Figure 26-22 shows a swimmer at distance $D = 38.0\text{ m}$ from a lightning strike to the water, with current $I = 78\text{ kA}$. The water has resistivity $30\text{ }\Omega\cdot\text{m}$, the width of the swimmer along a radial line from the strike is $0.70\text{ m}$, and his resistance across that width is $4.00\text{ k}\Omega$. Assume that the current spreads through the water over a hemisphere centered on the strike point. What is the current through the swimmer?