Fundamentals of Circuits I: Current Models, Batteries & Bulbs

More documents

Recommendations

Info

Name: Date: Lab Partners: Fundamentals of Circuits I: Current Models, Batteries & Bulbs Objectives • To understand the nature of electric currents and why the current is the same at all points in simple circuits. • To understand that an electric potential difference (voltage) can cause a flow of electric charge in a conductor. • To gain practice in designing and building simple circuits with batteries, light bulbs and switches. • To learn to draw circuit diagrams using electrical symbols. • To learn to make measurements of current ant voltage using microcomputer-based probes Overview In the labs during the first part of this semester you are going to do a series of activities designed to help you develop a strong conceptual understanding of the nature of electric current and electric potential difference (commonly referred to as Voltage), and the essential features of simple electric circuits. These labs have been adapted from the Real Time Physics Active Learning Laboratories [1]. The goals, guiding principles and procedures of these labs closely parallel the implementations found in the work of those authors [1, 2, 3]. The ideas that you will learn in these labs are the same ones that go into making all the electrical devices that play an important role in our modern world-everything from electric lights and motors to TV sets, computers and photocopy machines. In several of these labs the electrical components we will work with are batteries and light bulbs. A battery is a device that uses chemical energy to do work on the electric charges that flow in it. As it does work it increases the electrical potential energy of these charges, which generates an electric potential difference. The energy added to the electric charge by the battery can be used to operate an electrical device. In today’s experiment that device will be a light bulb. But in order to deliver the energy to the light bulb the electric charge must flow through the battery and light bulb. This requires the light bulb and battery to be connected using conductors, materials that allow electric charges to flow in them. In this lab you will consider several models that might explain the flow of charge and predict the measurements that would result if the model is correct. You will then make the measurements to determine which of the models correctly describes the flow of charge, and which models do not. PHYS-204: Physics II Laboratory 1
Fundamentals of Circuits I: Current Models, Batteries & Bulbs v 0.1 Investigation 1: Models describing electric current What is electric current Today, as you can read in any textbook, we believe that current is produced by electric charges in motion. The electric current in a copper wire, for example is produced by the motion of electrons through the wire. Do we know this If so, how do we know How can we experimentally distinguish this model of current from other models These questions were studied and tested by Michael Faraday, a famous early nineteenth century scientist. Faraday examined the effects of electricity from many different sources, including animals such as electric eels, batteries, and electromagnetic induction in addition to the electric charge produced by rubbing objects, and concluded that ”electricity, whatever may be its source, is identical in its nature.” Let’s put Michael Faraday’s conclusion to a small test. Is the electricity in “static electricity” identical in nature to the electricity in a battery or power supply Objects which are rubbed in particular ways are found to attract or repel other objects which have been rubbed in particular ways. These forces between objects are attributed to a property of matter known as charge. Rubbing the objects produces and induced charge on the objects. This induced charge is an example of static electricity. The purpose of the first activity is to compare the current produced the static charges deposited by rubbing materials together. to the current produced by a battery or power supply. You will observe a demonstration using the following materials: • Large variable capacitor with two metal plates • Electroscope • foil covered Styrofoam ball on a string • 300 V battery pack or power supply • PVC rod and wool cloth • acrylic rod and polyester or silk cloth • alligator clip leads Activity 1.1: Comparing charge from a power supply and charge produced by rubbing Step 1: The metal plates of a variable capacitor and the conducting ball will be set up as shown in Fig. 1. By charging the metal plates in two ways, we can test whether or not the different charging methods have different effects on the ball dangling between the plates. The two methods we will test are: a. Electrostatic Charging by Rubbing. Stroke one plate with a PVC (gray) rod that has been rubbed with the cat fur or wool. Repeat this several times. Stroke the other plate with the acrylic (clear) rod that has been rubbed with the silk or polyester cloth. PHYS-204: Physics II Laboratory 2
Page 1: Name: Lab Partners: Date: Pre-Lab A
Page 5 and 6: Fundamentals of Circuits I: Current
Page 19: Fundamentals of Circuits I: Current

Fundamentals of Circuits I: Current Models, Batteries & Bulbs

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?