Static electricity lab report

Physics Lab (Online Simulation) Charges and Fields Introduction to Static Electricity Electricity and Light Unit 1 TA name: Due Date: Student Name: Student ID: This lab uses the Balloons and Static Electricity John Travoltage and Charges and Fields Remote lab simulation from PhET Interactive Simulations at University of Colorado Boulder, under the CC-BY 4.0 license. Learning Goals: Students will be able to A. Describe and draw models for common static electricity concepts. (transfer of charge, induction, attraction, repulsion, and grounding) B. Determine the variables that affect how charged bodies interact C. Predict how charged bodies will interact D. Describe the strength and direction of the electric field around a charged body E. Use free-body diagrams and vector addition to help explain the interactions F. Compare electric fields to gravitational fields Theory: An Electric Field is a region in space in which electric forces act on electric charges. The Electric Field strength for any point in space is defined as the net Electric (Coulomb) Force per unit of positive charge acting on a charge placed at that point, i.e.,   E=F [1] q The SI unit for electric field is Newton / coulomb (N/C), or (more practically) volt/meter, (V/m). The direction of an electric field at any point is defined as the direction of the net electric force on a positive charge placed at that point. Since, F = k q1q2/r2 (Coulomb’s Law), the Electric Field can be written in the form E = kq/r2 where r is the distance from the charge. Faraday introduced the concept of lines of force to aid in visualizing the magnitude and direction of the total electric field about a charge or collection of charges. These concepts are listed below. 1. A line of force is everywhere tangent to the electric field direction. 1 Physics Lab (Online Simulation) 2. The lines of force originate on positive charges and terminate on negative charges. 3 The density of the lines of force (i.e. the lines/cm or lines/cm2) in a region of space is used to represent the electric field strength in that region of space. 4 Lines of force will not cross over or touch one another. Electric fields can be represented by a scaled drawing, by first choosing a scale factor (proportionality factor) so that n number of lines/cm2 represent a certain value of field strength (volts/m). (b) (a) Figure 1 Examine the figure above. The two figures represent an electric field departing a charged sphere. If we let figure 1(a) represent an electric field with field strength of E, figure 1(b) would represent an electric field with field strength of 2E. (Twice the numbers of field lines depart the charge). In this experiment, we may estimate the electric field at certain points from the potential gradient, at these points E = V/x = (V2 – V1) / (x2 – x1) [2] Where V1 and V2 are the potential of two adjacent equipotential lines and (x2 – x1) is the distance between the lines in meters. It is possible to find any number of points in an electric field, all of which are at the same potential (voltage). If a line or surface is constructed such that it includes all such points with equal potential, the line or surface is known as an equipotential line or surface An expenditure of work is required when moving a charge parallel to the direction of the electric field. To move between one equipotential line to another, an amount of work is required to satisfy the laws of conservation of energy. From mechanics it is known that W = Fd. From equation [1] it can be found that F = qE. Therefore the work to move a charge can be determined by combining the two equations to obtain W = qEd. However, when a charged is moved along an equipotential line or surface, it is moving in a direction perpendicular to the electric field and therefore no expenditure of work is needed to move the charge. This pre-lab is worth 5 points. 2 Physics Lab (Online Simulation) This pre-lab is worth 5 points. 1) What is an electric field? 2) What are the units for an electric field? List both of them. 3) What is an equipotential line? 4) Lines of force originate on ________________ charges and terminate on ________________charges. 5) Electric field lines are (parallel, perpendicular) to the equipotential lines. 3 Physics Lab (Online Simulation) Static Charges 1. Open Balloons and Static Electricity, then explore to develop your own ideas about electrical charge.