Standard electrocardiography measures time-dependent potential differences between multiple points on the body, giving cardiologists multiple perspectives on the heart?s electrical activity. In contrast, Fig. 22.26 is a ?snapshot? showing a more detailed picture at an instant of time. The lines are equipotentials on the surface of a human torso, associated with the heart?s electrical activity. Relative to the line marked V = 0, the potential is negative to the upper left (black) and positive to the lower right (color).

The electric field in region A is approximately

a. 20 ?N/C.b. 2 mN/C.c. 20 mN/C.d. 2 kN/C.

V = 0 V = -0.5 mV V= 0 FIGURE 22.26 Equipotentials on a human toro (Passage Problems 82-85)