Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Make enough copies of the Electric Field Plotting Map for each student to graph the multiple configurations that will be tested.
2. Cut out 10" x 13" cardboard sheets for every lab group.

Safety Precautions

Silver conducting ink is considered nonhazardous. However, as with all chemicals, avoid contact with skin and eyes, as it may cause irritation. Pushpins are sharp; use caution when handling. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines.

Disposal

The silver conductive pen should last for about one year if the pen is capped and stored properly. It may be discarded when dry.

Lab Hints

• This laboratory activity can be completed in two 50-minute class periods. It is important to allow time between the Introductory Activity and the Guided-Inquiry Activity for students to discuss and design the guided-inquiry procedures. Also, all student-designed procedures must be approved for safety before students are allowed to implement them in the lab. Prelab Questions may be completed before lab begins the first day.
• When mapping the electric field lines, using a higher voltage than 9V may make the measurement process easier. A higher voltage difference will make it easier to pinpoint the highest voltage reading. Likewise, the farther apart the two voltmeter leads are fixed, the greater the potential difference will result. The tradeoff in the latter case is less distinct field lines.
• If students are unsure how to get the voltmeter leads to remain a fixed distance apart, suggest taping a pen cap between them.

Teacher Tips

• Experiment with insulators by cutting out shapes from the conductive paper. The absence of conducting materials will demonstrate the nonconducting properties of insulators and their effects on electric fields.
• 60 to 80 meters may be drawn with a single silver conducting ink pen before it runs dry.

Further Extensions

Opportunities for Inquiry
When applying the concept of the electric field, there is usually more than one source charge. Design an experiment that would allow one to determine the direction of the force on a test charge placed in varying locations in a configuration that includes four source charges. There are two positive and two negative source charges. Each source charge is at the corner of a “square” with like charges on opposing corners.

Alignment to the Curriculum Framework for AP^® Physics 2

Enduring Understandings and Essential Knowledge
An electric field is caused by an object with electric charge. (2C)
2C1: The magnitude of the electric force, F, exerted on an object with electric charge q by an electric field E is F = qE. The direction of the force is determined by the direction of the field and the sign of the charge, with positively charged objects accelerating in the direction of the field and negatively charged objects accelerating in the direction opposite the field. This should include a vector field map for positive point charges, negative point charges, spherically symmetric charge distributions, and uniformly charged parallel plates.
2C2: The magnitude of the electric field vector is proportional to the net electric charge of the object(s) creating that field. This includes positive point charges, negative point charges, spherically symmetric charge distributions, and uniformly charged parallel plates.
2C3: The electric field outside a spherically symmetric charged object is radial, and its magnitude varies as the inverse square of the radial distance from the center of that object. Electric field lines are not in the curriculum. Students will be expected to rely only on the rough intuitive sense underlying field lines, wherein the field is viewed as analogous to something emanating uniformly from a source.
2C4: The electric field around dipoles and other systems of electrically charged objects (that can be modeled as point objects) is found by vector addition of the field of each individual object. Electric dipoles are treated qualitatively in this course as a teaching analogy to facilitate student understanding of magnetic dipoles.
2C5: Between two oppositely charged parallel plates with uniformly distributed electric charge, at points far from the edges of the plates, the electric field is perpendicular to the plates and is constant in both magnitude and direction.

Physicists often construct a map of isolines connecting points of equal value for some quantity related to a field and use these maps to help visualize the field. (2E)
2E1: Isolines on a topographic (elevation) map describe lines of approximately equal gravitational potential energy per unit mass (gravitational equipotential). As the distance between two different isolines decreases, the steepness of the surface increases. (Contour lines on topographic maps are useful teaching tools for introducing the concept of equipotential lines. Students are encouraged to use the analogy in their answers when explaining gravitational and electrical potential and potential differences.)
2E2: Isolines in a region where an electric field exists represent lines of equal electric potential, referred to as equipotential lines.
2E3: The average value of the electric field in a region equals the change in electric potential across that region divided by the change in position (displacement) in the relevant direction.

Learning Objectives
2C1.1: The student is able to predict the direction and the magnitude of the force exerted on an object with an electric charge q placed in an electric field E using the mathematical model of the relation between an electric force and an electric field: F = qE ; a vector relation.
2C1.2: The student is able to calculate any one of the variables—electric force, electric charge, and electric field—at a point given the values and sign or direction of the other two quantities.
2C2.1: The student is able to qualitatively and semiquantitatively apply the vector relationship between the electric field and the net electric charge creating that field.
2C3.1: The student is able to explain the inverse square dependence of the electric field surrounding a spherically symmetric electrically charged object.
2C4.1: The student is able to distinguish the characteristics that differ between monopole fields (gravitational field of spherical mass and electrical field due to single point charge) and dipole fields (electric dipole field and magnetic field) and make claims about the spatial behavior of the fields using qualitative or semiquantitative arguments based on vector addition of fields due to each point source, including identifying the locations and signs of sources from a vector diagram of the field.
2C4.2: The student is able to apply mathematical routines to determine the magnitude and direction of the electric field at specified points in the vicinity of a small set (2–4) of point charges, and express the results in terms of magnitude and direction of the field in a visual representation by drawing field vectors of appropriate length and direction at the specified points.
2C5.1: The student is able to create representations of the magnitude and direction of the electric field at various distances (small compared to plate size) from two electrically charged plates of equal magnitude and opposite signs and is able to recognize that the assumption of uniform field is not appropriate near edges of plates.
2C5.2: The student is able to calculate the magnitude and determine the direction of the electric field between two electrically charged parallel plates, given the charge of each plate, or the electric potential difference and plate separation.
2C5.3: The student is able to represent the motion of an electrically charged particle in the uniform field between two oppositely charged plates and express the connection of this motion to projectile motion of an object with mass in the Earth’s gravitational field.
2E1.1: The student is able to construct or interpret visual representations of the isolines of equal gravitational potential energy per unit mass and refer to each line as a gravitational equipotential.
2E2.1: The student is able to determine the structure of isolines of electric potential by constructing them in a given electric field.
2E2.2: The student is able to predict the structure of isolines of electric potential by constructing them in a given electric field and make connections between these isolines and those found in a gravitational field.
2E2.3: The student is able to qualitatively use the concept of isolines to construct isolines of electric potential in an electric field and determine the effect of that field on electrically charged objects.
2E3.1: The student is able to apply mathematical routines to calculate the average value of the magnitude of the electric field in a region from a description of the electric potential in that region using the displacement along the line on which the difference in potential is evaluated.
2E3.2: The student is able to apply the concept of the isoline representation of electric potential for a given electric charge distribution to predict the average value of the electric field in the region.

Science Practices
1.2 The student can describe representations and models of natural or man-made phenomena and systems in the domain.
1.4 The student can use representations and models to analyze situations or solve problems qualitatively and quantitatively.
2.2 The student can apply mathematical routines to quantities that describe natural phenomena.
2.3 The student can estimate numerically quantities that describe natural phenomena.
3.1 The student can pose scientific questions.
4.1 The student can justify the selection of the kind of data needed to answer a scientific question.
4.2 The student can design a plan for collecting data to answer a particular scientific question.
4.3 The student can collect data to answer a particular scientific question.
5.1 The student can analyze data to identify patterns and relationships.
5.2 The student can refine observations and measurements based on data analysis.
6.1 The student can justify claims with evidence.
6.2 The student can construct explanations of phenomena based on evidence produced through scientific practices.
6.4 The student can make claims and predictions about natural phenomena based on scientific theories and models.
7.2 The student can connect concepts in and across domain(s) to generalize or extrapolate in and/or across enduring understanding and/or big ideas.

Answers to Prelab Questions

1. Two small, oppositely charged spheres are placed 10 m from each other and then brought closer until they are 5 m from each other.
   1. By what factor did the force between the charges change?

      The force increased by a factor of four. Coulomb’s law (Equation 2) obeys an inverse square law.

      {14012_PreLabAnswers_Equation_1}
   2. Is it an attractive or repulsive force?

      It is an attractive force.

2. A source charge exerts a force of 20 N on a positive charge of 5 μC that is 3 m away.
   1. What is the magnitude of the electric field between the source charge and the positive charge?

      E = F/q
      E = 20 N/5 μC = 20 N/5 x 10^–6 C
      E = 4,000,000 N/C

   2. What is the magnitude of charge on the source charge?

      F_e = kq₁q₂/r²

      {14012_PreLabAnswers_Equation_4}

      F_e = 20 N
      r = 3 m
      k = 9 x 10⁹ C²/N•m²
      q₂ = 5 x 10^–6 C

      {14012_PreLabAnswers_Equation_5}

      q₁ = 0.004 C

3. The same red beach ball is placed on different hills. Rank the pictures in terms of which ball has the most gravitational potential energy.
   {14012_PreLabAnswers_Figure_1}
   In pictures B and C, the red beach ball has equivalent gravitational potential energy. In picture A, it has the lowest.

Sample Data

Introductory Activity

Sample Electric Field Maps

Analyze the Results <

• What would change about the 1 volt equipotential lines if the power supply was set to 6 volts instead of 9 volts?

  The equipotential lines would be farther apart.

• If set to 6 volts, what would the voltmeter read at the same point where the 4.5 volts were measured for a 9 volt supply?

  The voltmeter would read 3 volts instead of 4.5 volts.

• What would a gravitational equipotential line look like on a map that shows elevation (topographic map)? What does a gravitational equipotential line represent?

  The gravitational potential lines are the lines of equal elevation on a topographic map. These lines are an indication of elevation; if one is to walk on this “line,” one would remain at the same elevation.

Guided-Inquiry Activity

Part A. Discussion Questions Analyze the Results

• What does the line in step 10 represent? Does it have a direction?

  This line represents an electric field line. It has a direction away from the positive electrode and towards the negative one. Its direction is always perpendicular to the equipotential lines.

• How does the line in step 10 relate to the equipotential lines drawn in the Introductory Activity?

  This line is perpendicular to the equipotential lines.

• Draw an estimate of what the remaining electric field vectors would look like for the dipole charge setup.
  {14012_Data_Figure_8}
• Where is the field mostly uniform, showing lines most evenly spaced? Why might this be so?

  The field is mostly uniform nearest the two point charges, where the individual charge has a greater effect than the charges farther away.

• The two electrodes tested were opposite charges. Sketch your best guess for the field lines of two same-charge point electrodes.

  Student answers will vary.

  {14012_Data_Figure_9}

Part B. Sample Procedure

Select the positive conductor in your respective configuration and carry out an analogous procedure to what was done in the introductory and guided-inquiry activities.

Analyze the Results 

• In your own words, describe the electric field between the plates.

  The electric field between the plates is uniform with straight lines pointing directly to the negatively charged plate.

• What happens to the field lines and equipotential lines near the top and bottom edges of the plates?

  The field begins to warp near the edges of the plate and is no longer uniform. In the same way, the equipotential lines begin to curve rather than staying straight.

• In your own words, describe the electric field between the large conductor and point source.

  The electric field between the large conductor and point source is uniform with straight lines pointing directly from the large conductor to the point source.

• What happens to the field and equipotential lines outside of the large conductor?

  The electric field is contained within the large conductor. There is no measurable field outside of the large conductor and therefore no equipotential lines.

• When comparing a single point charge to a gravitational analogy, what comparisons can be drawn between the electric field and acceleration due to gravity? What would the magnitude of the gravitational field be?

  The value of the electric field is directly analogous to the acceleration due to gravity. The magnitude of the gravitational field is 9.8 m/s², the average acceleration due to gravity on Earth.

• Why must the electric field vectors and the equipotential lines be perpendicular? Recall that acceleration is a vector. Why is the acceleration due to gravity perpendicular to gravitational equipotential lines?

  The equipotential lines represent points in space that are at the same voltage, or potential energy per unit charge. The field vectors represent the direction of greatest electric potential change. In the same way, a vector representing the acceleration due to gravity is perpendicular to gravitational equipotential lines because straight down (or up) is the direction of greatest gravitational potential change. The direction of greatest change and direction of no change must be as wide an angle apart as possible, which is perpendicular.

Answers to Questions

Guided-Inquiry Activity

Part A. Discussion Questions

1. Beach balls, each with a mass of 1 kg, are placed on three separate hills (see Figure 6).
   {14012_Data_Figure_6}
   1. How does the gravitational potential energy of the ball on hill A compare to the gravitational potential energy of the ball on hills B and C?

      The gravitational potential energy of the ball is the same on all three hills.

   2. The dotted line on each hill is a gravitational equipotential line. If the ball is rolled around the hill parallel to this line, its potential energy will remain the same. Now you are asked to roll the ball up the hill. Which hill would allow for the greatest instantaneous change in gravitational potential energy?

      Hill B would allow for the greatest instantaneous change in gravitational potential energy.

   3. The beach balls are now at the top of each hill. If a line is drawn from the top of the hill to the initial position of each ball in Figure 6, which line is closest to being perpendicular to the gravitational equipotential line?

      The line from the top of hill B to the initial position of the ball is closest to being perpendicular to the gravitational equipotential line.

   4. What angle does a vector representing the force on the ball due to gravity make with the gravitational equipotential line?

      A vector representing the force on the ball due to gravity makes a 90° angle with the gravitational equipotential line.

2. Consider the positively charged object below (see Figure 7). Its electric field vectors are shown.
   {14012_Data_Figure_7}
   1. Draw what you think the electric equipotential lines would look like around this charge.

      The equipotential lines would look like concentric circles centered on the charge.

      {14012_Data_Figure_10}
   2. What is the relationship between the equipotential lines and the electric field lines?

      The equipotential lines and the electric field lines are perpendicular to each other.

Review Questions for AP^® Physics 2

1. An uncharged hollow conductor is placed in between two conducting parallel plates separated by 60 cm. The plates are hooked up to a 12-V power supply with the positive lead on the left-hand plate and the negative (ground) lead on the right-hand plate.
   {14012_Answers_Figure_1}
   1. For the configuration above, draw what the equipotential lines would look like. Draw what the electric field vectors would look like.
      {14012_Answers_Figure_2}
   2. How does the hollow conductor affect the field? What is the field inside the hollow conductor?

      The hollow conductor reduces the magnitude of the electric field. The field inside of the hollow conductor is zero. It is zero because the free electrons move (toward the positive plate) in response to the external field created by the charged parallel plates. They accumulate on the left edge of the conductor until equilibrium is reached. Equilibrium arises from an opposing field created by the hollow conductor, the negative charge accumulation on the left and positive charge accumulation on the right cancel out the electric field and the net field inside the hollow conductor is zero.

   3. The hollow conductor is removed. What is the value of the electric field between the plates?
      {14012_Answers_Equation_1}

      d = 60 cm
      Δv = 12 cm
      12/0.6 m = 20 N/C

2. Draw what the electric field vectors look like in the configuration.
   {14012_Answers_Figure_3}
3. Consider this situation.
   {14012_Answers_Figure_4}
   1. Rank the points by order of increasing magnitude of the electric field.

      D, C, A, B

   2. Rank the points by order of increasing magnitude of the potential difference.

      D, C, A, B

   3. The potential difference between point B and point C is 2 V and they are 4 m apart. What is the average value of the electric field between points B and C?

      E = ΔV/Δd
      E = 2V/4 m
      E = 0.5 N/C

   4. Would the potential difference measured at point D change if a negative charge was placed there? Why or why not?

      No, it would not. The potential difference measured at point D (or any point) depends only on the sign and magnitude of the source charge.

4. A 0.1 C charge with a mass of 1 kg is accelerating at 9.8 m/s² toward a 100 kg fixed 10 C charge.
   1. What is the distance between the two charges?

      F = ma
      F = (1 kg)(9.8 m/s²)
      F = 9.8 N

      {14012_Answers_Equation_2}
      {14012_Answers_Equation_3}
      {14012_Answers_Equation_4}

      r = 30,304.58 m

   2. What is the acceleration due to gravity between the two charges?
      {14012_Answers_Equation_5}
5. Analyze the following situation. The negative –100 μC charge is 16 m from point A. The positive 20 μC charges are 12 m apart from each other. They are also equidistant from point A and from the negative charge. What is the direction and magnitude of the electric field vector at point A?
   {14012_Answers_Figure_5}

References

AP^® Physics 1: Algebra-Based and Physics 2: Algebra-Based Curriculum Framework; The College Board: New York, NY, 2014.

Introduction

We know that positive and negative charges attract, but how does this occur? Charges create electric fields, which then apply forces to the charges. The concept of electric fields is similar to gravitational fields, but often harder to understand. If an electric field is the medium through which electromagnetic forces interact, what does an electric field look like?

Concepts

• Electric field
• Electric potential
• Equipotential lines
• Coulomb’s law

Background

Both the force of gravity and electrostatic force describe interactions between fundamental units—mass for gravity and charge for electrostatics. The equation use to describe Newton’s law of gravitation is similar to the equation that describes Coulomb’s law. Both values drop by the inverse square of the distance—both are inverse square laws:

Gravitational fields are used to explain interactions between objects with mass. The more mass an object has, the stronger the gravitational field that surrounds it. For example, the acceleration due to gravity here on Earth is approximately 9.8 m/s² throughout most of the atmosphere. It is about 9.78 m/s² at the equator and 9.83 m/s² at the poles. The values are different because the surface at the poles is closer to the center of the Earth than at the equator. Therefore, the acceleration due to gravity can be regarded as the magnitude of the gravitational field caused by the Earth. The Earth is a source mass for this gravitational field (see Figure 1). An electric field is propagated from a source charge. The British scientist Michael Faraday (1791–1867) used the concept of an electric field to explain how charged bodies are able to exert forces at a distance without a medium to transport the energy. Faraday demonstrated the existence of an electric field by showing the effect a charged object would have on a small test charge. A test charge is not an actual physical reality, but a term we use to understand the effect conductors have on their space; if an actual charge were placed in the electric field, it would affect its surroundings and likewise exert a force on the surrounding charges.

An electric field is the force per unit charge given at a point in space. A positive test charge placed near a positive source charge experiences a repulsive force due to the electric field caused by the source charge. It is shown by the equation: where

E = electric field at the location of a test charge, N/C (newtons/coulomb)
F = force on the test charge, N (newtons)
q = positive test charge, C (coulombs)

This gravitational field–electric field analogy can be further extended by using the concept of high and low ground. A positive charge corresponds with “high” ground, a negative charge corresponds with “low” ground. Work done on an object, such as a ball, to bring it up a hill will increase its potential energy. Likewise, there is potential energy stored in electric fields—a positive test charge placed near another positive charge will experience a greater force than one that is far away. When released, a positive test charge will accelerate away from the positive charge and towards a negative one, and just like a ball rolling down a hill, will turn its potential energy into kinetic energy. The potential energy in electric fields is often expressed in terms of the potential energy difference between two points. The unit for electric potential difference, the volt (V), is defined as the potential difference between two points that would require one joule (J) of external work to move one coulomb (C) of charge from one point to the other (Equation 4). A volt can be expressed as the electric potential energy per unit charge. The average value of the electric field in a region equals the change in electric potential (V) across that region divided by the change in position in the relevant direction: where

E = average electric field, V/m (volts/meter)
ΔV = change in electric potential 
Δd = change in position (displacement)

Experiment Overview

The purpose of this advanced inquiry lab is to derive an understanding of the manifestation of an electric field and be able to deduct what electric field lines and equipotential lines would look like in any configuration. An introductory activity presents the concept of equipotential lines by mapping a dipole charge setup. The guided-inquiry activity explores how the electric field lines would look in a dipole setup and then considers other configurations of interest.

Materials

Prelab Questions

1. Two small, oppositely charged spheres are placed 10 m from each other and then brought closer until they are 5 m from each other.
   1. By what factor did the force between the charges change?
   2. Is it an attractive or repulsive force?
2. A source charge exerts a force of 20 N on a positive charge of 5 μC that is 3 m away.
   1. What is the magnitude of the electric field between the source charge and the positive charge?
   2. What is the magnitude of charge on the source charge?
3. The same red beach ball is placed on different hills. Rank the pictures in terms of which ball has the most gravitational potential energy.
   {14012_PreLab_Figure_2}

Safety Precautions

Silver conducting ink is considered nonhazardous. However, as with all chemicals, avoid contact with skin and eyes, as it may cause irritation. Pushpins are sharp; use caution when handling. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines.

Procedure

Introductory Activity

1. With the silver conductive pen, draw a dipole charge set up onto the conductive paper sheet (see Figure 3).
   {14012_Procedure_Figure_3}
2. Attach the conductive paper with the silver “electrode map” to the cardboard sheet using plastic pushpins, one pin into each corner, and insert a cork (see Figures 4 and 5).
   {14012_Procedure_Figure_4_Side view}
   {14012_Procedure_Figure_5_Top view}
3. Using aluminum pushpins, push one into each point on the silver conductor shapes—the pins will be the electrodes. Note: Do not push the pins all the way down into point charges, as the pin heads will cover the silver point charges. Instead, push in just enough to make electrical contact between the silver ink and the aluminum electrode (see Figure 4).
4. Attach one alligator lead from each pushpin electrode to the positive or ground (or “negative”) terminals of the power supply or battery. Set the power supply to 9 volts (see Figure 3). Note: When working with batteries, it is important to disconnect the wires when not in use, so as to not waste the battery or overheat the wires.
5. Using a voltmeter, hold the ground lead to the negative silver electrode on the field map. Note: Do not ground on the aluminum pins, as this will affect the results.
6. Using the positive lead of the voltmeter, slowly and carefully drag the lead across the conductive paper away from the electrode until the voltmeter reads 1 volt. Note: Be very careful dragging the leads, do not scratch the conductive paper!
7. Hold the positive lead at that point while a lab partner marks the spot on the Electric Field Plotting Map.
8. Keeping the negative voltmeter lead on the negative electrode, repeat step 6 towards a new point many times, marking each point on the map.
9. Repeat step 8 several times. Draw a best-fit line connecting the 1-V marks.
10. Repeat steps 6–9 to map 2-V, 3-V, 4-V, 5-V, 6-V, 7-V and 8-V marks. Note that any voltage difference may be chosen (e.g., 0.5-V, 2-V), as long as it is kept constant.
11. Repeat steps 6–9 for the the 4.5 volt mark.

Analyze the Results

• What would change about the equipotential lines if the power supply was set to 6 volts instead of 9 volts?
• If set to 6 volts, what would the voltmeter read at the same point where the 4.5 volts were measured for a 9 volt supply?
• What would a gravitational equipotential line look like on a map that shows elevation (topographic map)? What does a gravitational equipotential line represent?

Guided-Inquiry Design and Procedure
Form a working group with other students and discuss the following questions.

Part A.

1. Red beach balls, each with a mass of 1 kg, are placed on three separate hills (see Figure 6).
   {14012_Procedure_Figure_6}
   1. How does the gravitational potential energy of the ball on hill A compare to the gravitational potential energy of the ball on hills B and C?
   2. The dotted line on each hill is a gravitational equipotential line. If the ball is rolled around the hill parallel to this line, its potential energy will remain the same. Now you are asked to roll the ball up the hill. Which hill would allow for the greatest instantaneous change in gravitational potential energy?
   3. The red beach balls are now at the top of each hill. If a line is drawn from the top of the hill to the initial position of each ball in Figure 6, which line is closest to being perpendicular to the gravitational equipotential line?
   4. What angle does a vector representing the force on the ball due to gravity make with the gravitational equipotential line?
2. Consider the positively charged object (see Figure 7). Its electric field vectors are shown.
   {14012_Procedure_Figure_7}
   1. Draw what you think the electric equipotential lines would look like around this charge.
   2. What is the relationship between the equipotential lines and the electric field lines?
3. Set up the same charge configuration as the Introductory Activity and set the power supply to 9 V.
4. Place the negative voltmeter lead on any point on the 1 V equipotential line, mark this point on the Electric Field Plotting Map. Trying to keep the leads equidistant from each other, lightly brush the positive test lead against the conductive paper in a hemisphere (similar to drawing with a compass) to find the greatest voltage.
5. Mark the location of the positive lead on the Electric Field Plotting Map.
6. How could you ensure that the test leads remain equidistant from each other so that your readings are accurate? Make the necessary adjustments.
7. With the voltmeter leads at a fixed distance from each other, repeat steps 4 and 5.
8. Put the negative test lead at this new point as the new “ground.” Once again, lightly brush the positive test lead in a hemisphere, finding the greatest voltage. Mark this location and voltage, and set it again as new “ground.”
9. Repeat step 8, always carrying the line in the direction of the greatest voltage change, until the negative electrode on the conductive paper is reached.
10. To start a new line, pick a different spot on the 1-V equipotential line, and ground the negative test lead there. Repeat steps 8 and 9.

Analyze the Results

• What does the line in step 10 represent? Does it have a direction?
• How does the line in step 10 relate to the equipotential lines drawn in the Introductory Activity?
• Draw an estimate of what the remaining electric field vectors would look like for the dipole charge setup.
• Where is the field mostly uniform, showing lines most evenly spaced? Why might this be so?
• The two electrodes tested were opposite charges. Sketch your best guess for the field lines of two same-charge point electrodes.

Part B.

1. Depending on what has been assigned to your lab group, draw either the Charged Parallel Plates or Point Source in Large Conductor configuration with the conductive silver ink pen on an unused conductive paper sheet.
2. Remove the conductive paper sheet with the dipole charge configuration from the cardboard sheet.
3. Repeat step 2 of the Introductory Activity for the conductive sheet with either the Charged Parallel Plates or Point Source in Large Conductor configuration.
4. Design and carry out a procedure for mapping out the electric field and equipotential lines of the assigned configuration.

Analyze the Results

• In your own words, describe the electric field between the plates.
• What happens to the field lines and equipotential lines near the top and bottom edges of the plates?
• In your own words, describe the electric field between the large conductor and point source.
• What happens to the field and equipotential lines outside of the large conductor?
• When comparing a single point charge to a gravitational analogy, what comparisons can be drawn between the electric field and acceleration due to gravity? What would the value of the gravitational field be?
• Why must the electric field vectors and the equipotential lines be perpendicular? Recall that acceleration is a vector. Why is the acceleration due to gravity perpendicular to gravitational equipotential lines?

Student Worksheet PDF

14012_Student1.pdf