Phun with Electricity

In todays lab we will investigate a variety of subjects associated with electricity. Some of these phenomena you will have seen in class others will be new to you and hopefully you will be able to figure them out.

Part 1: Electrostatics: In this experiment we will use a device called an electroscope. Remove the cap from the top. Move the rod on your table near the ball on the top. What do you observe? Now vigorously rub the rod with the cloth provided on the table. Do this for a minute or so. Now move the rod near the top of the electroscope. What do you observe? Why does what you observe happen? Now place the metal cap back on and again rub the rod with the cloth. What do you observe now? What do you think is happening?









Part 2: A Hair Raising Experience: For this part we need a volunteer from the class. The volunteer will stand on a platform and place their hand on the dome of the Van de Graaff generator. The Van de Graaf generator romoves charge from the bottom of the device and moves this charge to the metal dome, the charge then goes to the surface of the dome. When the device is running what do you observe about our volunteer? Why does this happen?








Part 3: What conducts electricity? In this experiment you will use a very useful device that is called a digital voltmeter or what physics types call a DVM. This device can measure a variety of electrical quantities. Here we will use it to see what conducts electricity and what does not conduct. Turn on the DVM. On the DVM turn the knob to the area labelled with the Greek capital letter omega, omega is used since the unit of electrical resistance is an Ohm. Set the knob to the 200 ohm reading. With the metal ends of the black and red probes not touching what do you read on the DVM? This result of the DVM reading 1 tells you that the air between the probes does not conduct electricity. Now touch the ends together. What do you read? This number tells you that the probes will conduct electricity with a resistance of what you read. To determine if an object conducts electricity or not place both the black and red probes on the object. Make sure that the metal parts of the probes make good contact with the object and that the probes do not touch one another. Now pick a variety of objects around the lab and see what objects conduct and what do not and write these down. Just like the air objects that don't conduct will read OL on the DVM. What do the objects that conduct have in common? What do the objects that don't conduct have in common?











Part 4: Direct Current: Switch the knob on the DVM to the area on the upper left labelled DCV (Direct Current Voltage). Place the knob at the 200 level. This means that the DVM can read voltages up to 200 volts. We will measure the voltage output of the blue power supply on the table. Connect the red probe to the red output and the black probe to the black output making sure that the metal part of the probe is touching the metal part of the output. Why do you think the metal part of the probe has to touch the metal part of the output? Turn the power supply on. What do you read? Rotate the black knob on the power supply. What do you think this knob does? Now put the black probe on the red output and the red probe on the black output. What do you read?










Part 5: Alternating Current: Switch the knob on the DVM to the area on the upper right labelled ACV (Alternating Current Voltage). Place the knob on the 200 volt mark. Now we are going to do something you are told not to do. Put one of the probes in one of the vertical openings on the electric socket on your table. Make sure it is pushed as far in as possible. Now making sure that the two probes don't touch put the other probe in the other vertical opening of the electrical socket. What do you read? Now switch the probes at the socket. What do you read?








Part 6: Oscilloscopes. These are really cool devices that can be used to measure voltages as a function of time. They can tell you if the voltage is constant in time or if it is changing with time. Turn on the oscilloscope and play with it. Other than dropping it on the floor you cannot hurt it. Your instructor will come to each table and show you some neat things you can measure.