Download Material Properties and Selection for a Light Bulb: A Laboratory Experiment and more Lab Reports Materials science in PDF only on Docsity! 1 LAB I WHAT IS IN IT AND WHY? Study (Pre-Lab) Questions (Complete these BEFORE coming to lab, there will be Study/Pre-Lab Questions for each lab this quarter): 1. Make a list of 3 examples for each of the following material properties: 1. Mechanical properties 2. Electrical properties 3. Optical properties 4. Magnetic properties 5. Thermal properties 2. Define the five types of properties listed above in engineering terms, using descriptive text and/or equations. Use the glossary and the index in the text to help you. 3. Postulate the most important properties needed for the selection of a material for a stair railing. Consider railings that may be in the following environments: 1. in your home 2. in a place of business 3. outside How does usage change your list of most important properties? Using this information, develop a list of materials that you would choose for your railing for each of the environments specified. If you are sent out to build or buy these railings, what additional factors might you consider? How would these factors influence your choice of materials? I. Introduction All engineers are involved with materials on a daily basis. We manufacture and process materials; design and construct components or structures using materials; select materials, analyze failures of materials, or simply hope the materials we are using perform adequately. Materials may be classified into several groups: metals, ceramics, polymers, semiconductors, and composite materials. Materials in each of these groups possess different structures and therefore properties. 2 The purpose of this laboratory is to get you thinking about How? What? and Why? different materials are selected when designing a particular object common to our everyday lives. In this laboratory, you will disassemble a light bulb in order to understand why particular materials were selected for its various components. Since we will be examining the light bulb components from an engineering standpoint, we will want to consider the materials employed as they relate to the design and function of a light bulb. No materials selection decisions can be made without thorough consideration of the particular application of the material. Therefore, we will want to understand the overall design of the object itself as well as the various materials used to make the object. Here, our aim is towards a more complete understanding of the engineering decisions that are part of the design process. It is with this in mind that you should approach your analysis during this laboratory. There are two parts to this laboratory. In the first part, you will be measuring a material property for light bulbs. In the second part you will be disassembling and examining your light bulb. You should work together in groups with one light bulb per group. You should work cooperatively in your team during this lab; doing so will enhance your enjoyment and learning. The work in your lab notebook, however, should be your own. _____________________________________________________________________ PART I – MATERIAL BEHAVIOR OF A LIGHT BULB I. Background and Theory Ohm’s law states that the voltage across a piece of material (such as a wire) is proportional to the current through the material: V = I * R [Eq. 1] Where: – V is the applied potential field – voltage (volts - V) – I is the flow of electrons – current (Amps - A) – R is the resistance of the piece of material (ohms – Ω). R is a constant if the temperature of the conductor remains constant. If the temperature increases, the resistance increases for a metal and it decreases for a semiconductor. The increase in R for a metal is due to an increase in vibrations scattering the electrons which are the current carriers. For many metals R increases linearly with temperature. In the case of a light bulb, the resistance of the tungsten (W) used for the filament varies with temperature according to the following relation: 811.0 )300( )( 300 = R TRT [Eq. 2] In this equation T is the absolute temperature in Kelvin (K), and room temperature is assumed to be 300 K. R(T) is the resistance at the temperature T. R(300) represents the resistance at ambient room temperature. The absolute temperature in K is related to the temperature in C by the following relationship:
