Copy_of_PHYS140_The_Electric_Field_Lab_-_STUDENT_VERSION

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Siena College - General Physics 140 The Electric Field Lab NAME:Rebecah Leonard GROUP MEMBERS: Learning Goals 1. In Section I, you will observe and identify patterns involving objects that are able to interact without direct contact. You will then develop and relate the mechanisms by which gravitational and electrical interactions occur by using a field approach to explain how a source mass or charge can exert a force on test objects without direct contact. 2. In Section II, to quantify the mechanisms of gravitational fields and electric fields, you will relate the energy-like physical quantities of gravitational potential and electric potential through the analogy of topographical maps. 3. In Section III, you will utilize equipotential lines as a representational tool for showing the electric potential environment in the vicinity of charge distributions. 4. In Section IV, you will explain the outcome of an experiment qualitatively by using the relationship between E-fields and equipotential surfaces. Driving Questions: How is it possible that planets, stars, and other celestial objects exert gravitational forces on each other without any physical contact? How is it possible that an electrically charged object can cause the hairs on one’s arm or head to move without any physical contact? How are these two phenomena related? Section I - In this part of the lab, you will observe and identify patterns involving objects that are able to interact without direct contact. You will then develop and relate the mechanisms by which gravitational and electrical interactions occur by using a field approach to explain how a source mass or charge can exert a force on test objects without direct contact. Equipment: Stretch fabric, clamps, different mass spheres and marbles (all optional). Scientific Ability Missing Inadequate Needs Improvement Adequate B7 Is able to identify a pattern in the data No attempt is made to search for a pattern. The pattern described is irrelevant or inconsistent with the data. The pattern has minor errors or omissions. The pattern represents the relevant trend in the data. B9 Is able to devise an explanation for an observed pattern No attempt is made to explain the observed pattern. An explanation is vague, not testable, or contradicts the pattern. An explanation contradicts previous knowledge or the reasoning is flawed. A reasonable explanation is made. It is testable and it explains the observed pattern. 1

Siena College - General Physics 140 The Electric Field Lab Observe the following experiments involving interactions between spheres of different masses that are on top of a stretchy material. You can observe these experiments with the equipment setup for the entire class or with the video below. Then answer the questions that follow. https://www.youtube.com/watch?v=Pdq78yXiyR0 A. How is the path of the marble affected by the presence or absence of the heavy object? The marble gravitates to the heavy object in the center. When it’s two smaller objects they gravitate towards each other. B. How is the heavy object able to interact with the marble without actually touching it? The heavier object is able to change the plane that both objects rest on. C. Knowing that electric interactions can be attractive or repulsive, what can you do to instead make the marble move away from an object disturbing the blanket (to achieve this, you need to replace the ball with another object that disturbs the blanket in a different way). Instead of having the object rest on the blanket, you can put a bigger object underneath it. This way it is elevated where the object makes contact with the blanket. For each situation pictured in the table that follows, represent the gravitational force or the electric force that the source mass or source charge exerts on the test mass or test charge at the points shown. Draw the arrows with the correct relative lengths. Written Description Visual Description With arrows, represent the gravitational force that the Earth (the source mass) exerts on a small object (the test mass) at the points shown. 2

Siena College - General Physics 140 The Electric Field Lab With arrows, represent the electric force that the object with a large negative charge (the source charge) exerts on a small object that has a positive charge (called the test charge) at the points shown. With arrows, represent the electric force that the object with a large positive charge (the source charge) exerts on a small object that has a positive charge (called the test charge) at the points shown. 3

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Siena College - General Physics 140 The Electric Field Lab D. Use a field approach to explain how the source mass (or source charge) can exert a force on test masses (or test charges) without directly touching them. To come up with an explanation, think about how the presence of a source mass or a source charge alters its surrounding space. Is your explanation 4

Siena College - General Physics 140 The Electric Field Lab consistent with the experiments involving the spheres on a blanket? A source such as mass that creates a gravitational field and a charge that creates an electric field, so when a large mass comes into contact with a smaller mass it creates a gravitational force by gravitational field and a charge creates electric force by electric field. Yes it is consistent. E. For the gravitational field, discuss how the magnitude of the force may depend on the properties of the field such as the mass of the source object, and on the distance away from the source object. Consider similar factors for the electric field. The magnitude of gravitational field and electric field at a certain point is dependent on the magnitude of the mass and its charge. For the gravitational field it is directed to the center for. A positive charge is directed away from the center and negative charges are directed to the center. The larger the mass the shorter the force and the smaller the mass the longer force it creates. Section II - In this part of the lab, to quantify the mechanisms of gravitational fields and electric fields, you will relate the energy-like physical quantities of gravitational potential and electric potential through the analogy of topographical maps. Equipment: None. Scientific Ability Missing Inadequate Needs Improvement Adequate B5 Is able to describe what is observed without trying to explain, both in words and by means of a picture of the experimental setup No description is mentioned. The description is incomplete. No labeled sketch is present. Or, observations are adjusted to fit expectations. The description is complete, but mixed up with explanations or patterns. The sketch is present, but it is difficult to understand. Clearly describes what happens in the experiments both verbally and with a sketch. Provides other representations when necessary (tables and graphs). A9 Mathematical No representation is constructed. The mathematical representation lacks the algebraic part (the student plugged in the numbers right away), has the wrong concepts being applied, signs are incorrect, or progression is unclear. No error is found in the reasoning. However, there may not be fully completed steps to solve the problem or one needs considerable effort to comprehend the progression. No evaluation of the math in the problem is present. The mathematical representation contains no errors and it is easy to see the progression from the first step to the last step in solving the equation. The solver evaluated the mathematical representation. 5

Siena College - General Physics 140 The Electric Field Lab A contour map of a large hill is shown below with 4 points of interest (A, B, C, and D). All heights are given in meters. A. What do the contour lines on a topographic map represent? The contour lines represent the equipotential forces. B. Rank the points (A, B, C and D) in order of increasing gravitational potential. B> A= C>D C. Describe the motion of a ball initially placed at rest at point C. The ball will travel perpendicular to the equipotential line. D. What information does the spacing of the contour lines convey? The slope and steepness of the terrain. E. Describe the behavior of a test mass when it is released in a region where the lines are: 1. close together: it's a steeper slope and the acceleration of the mass is greater 2. widely separated: it’s a lower slope and the acceleration of the mass is smaller F. Below is a topographic map of the Siena College area. On the map, circle a region where it may be good to go sledding on a snowy day. How do you know you are correct? The golf course because it has steeper hills. 6

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Siena College - General Physics 140 The Electric Field Lab Consider the diagram below in which charges were packed closely together to form parallel plates. Suppose also that the potential difference between the plates of charge is 7.0 volts and that the equipotential lines are at 1.0 volt intervals. G. What do the lines in the diagram above represent? Explain your thinking. The lines where all the points have the same electric potential and these are equipotential lines. H. Rank points A,B,C,D,E and F in order of increasing electric potential, relative to the ground. B<C=E< D< F <A I. Calculate the electric potential difference between: 7

Siena College - General Physics 140 The Electric Field Lab 1. point A and the negative plate: 0v-6v = -6v 2. point B and the negative plate: 0-0=0v 3. point C and point A: 6-2=4v 4. point C and point B: 0-2=-2v J. Describe the motion of a positive charge placed at point E. How do you know? It will accelerate perpendicular to the equipotential line and towards a lower potential. The field lines are perpendicular to equipotential lines and field lines tell you the direction of the force on a positive charge. They point away from positive charge and towards negative charges. K. Describe the motion of a negative charge placed at point E. How do you know? It will accelerate perpendicular to the equipotential line and towards a higher potential. The negative charge has a force in the opposite direction of the positive charge. L. In general, can we say that if a charged object is free to move in an electric field, it will move from an area of high potential to an area of low potential? Explain your thinking. No, this will happen only if it has a positive charge because a negative charge moves from low to high. M. What information does the spacing between equipotential lines convey? How is this similar to the spacing between contour lines on a topographic map? It indicates the strength of the electric field because the closer the lines the stronger the field the farther apart the lines the weaker the field. N. Describe the behavior of a positive test charge when it is released where the lines are: 1. close together: it will accelerate faster 2. widely separated: the acceleration will be less Section III - In this part of the lab, you will utilize equipotential lines as a representational tool for showing the electric potential environment in the vicinity of charge distributions. Equipment: Flat pieces of metal (either aluminum foil strips or bare copper wire), hanging masses to act as point charges, clear shallow pan, power supply or 9V battery, voltmeter with electrical leads, water, transparency grid made 8

Siena College - General Physics 140 The Electric Field Lab from graph paper, copy of grid on graph paper, colored pencils. Scientific Ability Missing Inadequate Needs Improvement Adequate G4 Is able to record and represent data in a meaningful way The data is either absent or incomprehensible. Some important data is absent or incomprehensible. The data is not organized in tables or the tables are not properly labeled. All important data is present, but it is recorded in a way that requires some effort to comprehend. The tables are labeled, but the labels are confusing. All important data is present, organized, and recorded clearly. The tables are labeled and placed in a logical order. A2 Is able to construct new representations from previous representations No attempt is made to construct a different representation. Representations are attempted, but use incorrect information or the representation does not agree with the information used. Representations are created without mistakes, but there is information missing, i.e. labels, variables. Representations are constructed with all given (or understood) information and contain no major flaws. Experimental Procedure 1. SAFETY CHECK: Make sure the power supply is NOT CONNECTED TO THE SETUP . Turn the power supply ON . Using the coarse and fine knobs, set the potential across the plates to 6.0 V. Then, turn the power supply OFF . 2. Place the transparency grid under the clear pan. Set the two flat pieces of metal in the pan. The flat pieces of metal should be aligned with the grid below. Hold down the two pieces of metal with insulating material if necessary. 3. Connect the pieces of metal to the power supply. 4. Fill the clear pan with about 1 cm (~500 mL) or so of water. 5. Turn the power supply ON . 6. Place the black (negative) probe from the voltmeter on the negative plate. This will be designated ground (0 V). 9

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Siena College - General Physics 140 The Electric Field Lab 7. Probe the space between and around the metal with the red (positive) probe from the voltmeter. You will be looking for points of equal potential from which you will construct an electric potential version of a "topographic map". 8. Record the corresponding voltage values on your own grid. 9. Replace the flat metal with two hanging masses. 10. Repeat steps 1-8. 11. Once your data is collected, you should connect the points of equal potential to form the equipotential "contour lines" for both sets of data. You should draw in the E-field lines as well. There is a relationship between E-field lines and lines of equal electric potential. Use different colors to distinguish equipotential lines from E-field lines. Include an image of each of your completed grids below. Section IV - In this part of the lab, you will explain the outcome of an experiment qualitatively by using the relationship between E-fields and equipotential surfaces. Equipment: None. 10

Siena College - General Physics 140 The Electric Field Lab Scientific Ability Missing Inadequate Needs Improvement Adequate B7 Is able to identify a pattern in the data No attempt is made to search for a pattern. The pattern described is irrelevant or inconsistent with the data. The pattern has minor errors or omissions. The pattern represents the relevant trend in the data. B9 Is able to devise an explanation for an observed pattern No attempt is made to explain the observed pattern. An explanation is vague, not testable, or contradicts the pattern. An explanation contradicts previous knowledge or the reasoning is flawed. A reasonable explanation is made. It is testable and it explains the observed pattern. In the video below, you see two metal plates connected to a device called a voltmeter that allows you to measure the potential difference between two points. Watch the video and answer the following questions. https://youtu.be/YO9j51QavmE A. How is it possible for the voltmeter to measure a positive potential difference if the experimenter only charged one plate? Hint: Note that the yellow wire in the experiment is connected to Earth. A voltmeter has to be parallel to the element that it’s measuring and it gets the distance from one plate to the other. B. Why does the experimenter move the plate using a plastic holder? If the person touched the plates it would change the charges that were there. C. Why does the reading of the voltmeter increase as the plate is moved to the right although no more charges were added to it? Think of how you can also explain the outcome by using the relationship between the E-field and equipotential surfaces. Since v=w/Q and work can be interpreted as F(delta x). So V= F(delta x)/Q as the distance increases so does V and as distance decreases so does V. D. Draw E-field lines for the electric field whose equipotential surfaces look as follows. Explain your thinking. (Not able to draw lines on diagram) 11

Siena College - General Physics 140 The Electric Field Lab The E-field is perpendicular to the V’s given. 12

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Copy_of_PHYS140_The_Electric_Field_Lab_-_STUDENT_VERSION

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