Question

2. The earth contains a mixture of minerals and moisture that make it a very good conductor of electricity. Therefore, it is possible to wire any circuit using the earth as the return path for the current. For example, to power a light-bulb connect the positive end of the battery to the light-bulb, the negative end of the battery to the ground, and the other end of the light bulb to ground as well. This is the top circuit illustrated. (a) The resistance of your arm from your palm to your shoulder is about 150 2. Estimate the resistance of your body from your palm to the soles of your feet. Explain. (b) An electric fence consists of a wire connected to one terminal of a voltage source; the other terminal of the voltage source is connected to ground. This is the bottom circuit illustrated. If the voltage Δ V is i 20V and you touch the fence with your hand while standing on the ground in your bare feet, how much power will your body absorb while in contact with the wire?

Answer 1

Sole to shoulder is approximately double the length from palm to shoulder but is approximately 4 times. We know that resistance is defined as $R = \rho \frac{L}{A}$ Hence resistance from shoulder to sole will be about half as compared to palm-shoulder. Hence total resistance = 150 + 150/2 = 150 +75 = 225 ohm

2) Power is defined as $P = \frac{V^2}{R}$        = 120² / 225 = 64 J/s