<p> Physics Pre-lab 212P-3</p><p>Electric Fields and Electric Potential</p><p>Name:______Section:_____ Date:______</p><p>(Read this & answer the questions before coming to lab)</p><p>Summary of relevant concepts: a) The electric potential energy U of a charge at any point in space is defined as the negative of the work done by the electric field E when the charge is moved from infinity to that point. Here, we define the electric potential at infinity to be 0. Note that this definition is equivalent to saying: "electric potential energy is the work YOU have to do in bringing a charge from infinity to that point." b) The electric potential V at any point in space is defined as the negative of the work done by the electric field when a charge of +1 C is brought from infinity to that point i.e.</p><p>A   V = -тE · ds Ҙ c) We also talk about the potential difference between two points A & B: B   DV = - E · ds тA d) i.e. the negative of the work done by the electric field in moving a charge of +1C from A to B. e) Electric potential and potential differences are measured in VOLTS; electric potential energy is measured in joules. f) Equipotential surfaces are a convenient way of picturing the electric potential in any region. Most often, equipotential LINES are used to portray a cross-sectional view of equipotential surfaces. By definition, all points on an equipotential line/surface have the same potential. Pre-lab Questions:</p><p>Q1. What is a "conservative force?" (Recall: Physics 211.) </p><p>______</p><p>______</p><p>Q2. When a mass that is free to move is released in the presence of a gravitational field, does it move from a region of high gravitational potential to a region of low gravitational potential or vice-versa?</p><p>______</p><p>______</p><p>Q3. When a charge that is free to move is released in the presence of an electric field, does it move from a region of high electric potential to a region of low electric potential or vice-versa? Does your answer depend on whether the charge is positive or negative? Why/why not?</p><p>______</p><p>______</p><p>______</p><p>______</p><p>______</p><p>______</p><p>______</p><p>______The figure below shows a region of space with a uniform electric field E. You can move charges from A to B along the three different paths shown. ACBD is a square of side L. </p><p>Q4. Suppose a positive charge +q is moved from A to B. Calculate the work W done by the electric field on the charge, if the charge +q were taken: </p><p>(a) first from A to C and then from C to B. </p><p>(b) first from A to D and then from D to B. Q5. Calculate the work done by the electric field on the charge if the charge were moved along the straight line AB. How does this compare with your answers to Q4? </p><p>Q6. From your answers to Q4 & Q5, what is the potential difference V = VB - VA between points A and B ?</p><p>Q7. An equipotential surface is defined as a surface on which there is no potential difference between any of the points. What are the equipotential surfaces for the problem above? Sketch a cross-sectional view of a few equipotential surfaces, showing surfaces with a constant potential difference between them. </p>