Investigation II: What is your resistance? You have a resistance in your body, which means that current can flow through your body. Small currents aren't a big deal (in fact all the cells in your body create their own currents to move ions and many other things around), but big currents can cause electrocution. In this procedure, you'll use the meters to measure your own resistance and then see how that varies through different body parts when they are wet and dry. After that, you'll measure the resistance of some objects that you can find around your house. A video on moodle will help you set this up this if you're working at home. 1. Use the meters to measure your internal resistance with dry hands. Place one probe in each hand as shown in the photo to the right, and record the smallest value that you measure in the table. Turn the dial to the 2000K setting in the section labeled "SQ" and then go down from there if you can to obtain the most precise reading possible. The red probe should be in the middle socket, black probe in the bottom socket, and top socket empty. (Figure 1) Figure 1: To measure the resistance between your hands, hold the two probes like this. 2. Have you ever heard that electricity and water don't mix? This is because water is an excellent conductor. Measure how your internal resistance changes when you're in water by sticking your fingers under water while they're holding the probes. (Figure 2) 3. Not all body parts have the same resistance. Find the resistance for a few more body parts and write the results in the table. Pay close attention to how wet your skin is because wet skin has a much smaller resistance than dry skin. Note: you'll likely observe that it's Figure 3: To measure the the wetness of your skin, and not the distance between the body parts, that matters most. Inside, your body is mostly water so it is an excellent conductor with very little resistance. (Figure 3). resistance under water, dip your hands in water while they're holding the probes. Figure 2: On the left, my dry skin measures >2000k2 On the right, a thick layer of lotion 4. I've reminded you several times this semester that when you use the meters you should be careful not to touch both of the probes because you'll be hooking yourself up parallel with the circuit. Let's test how much this matters by measuring the resistance the three resistors in this lab when 085 moistened my skin, and now the resistance is 443k2 you are touching both sides of the probe. (Figure 4) 5. Find a few common household objects and measure their resistance. Record those values in the table below. Try to make sure you get a good mix of insulators and conductors. You will likely need to use a variety of different settings - if the resistance is small, use the 2000 2 or 200 2 settings. If the number is large, use the 20k , 200k 2, or 2000k 2 settings. If the meter Figure 4: This is how NOT to use a meter. I'm touching both probes, so I am hooked up in parallel with this resistor. The reading I see is 85kkfor this 100k2 resistor - a huge error! records "1" on the 2000K setting, then this means that the resistance is >2000k2 (this will happen if you are measuring an insulator). Question 2-1: Why did the resistance between your two hands get smaller when they were wet? Question 2-2: Conductors are objects that have a small resistance to the flow of charge, which means they can easily support a current. What types of household objects were conductors? Insulators?