physics lab

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Augusta Technical College

PHYS 1110L - Online Lab 4: Electric Charges and Fields

Objectives:

The objective of this activity is to investigate and the magnitude and direction of the electric fields

due to various charge distributions and investigate the electric forces between point charges using

simulation software.

Equipment:

• Computer

• PhET Charges and Fields Simulation Software

• PhET Electric Hockey Simulation Software

Theory:

Electric Field Lines

Positive Point Charge

Negative Point Charge

Two Positive Charges

Electric Dipole

• The electric field at a point near an electric charge is the electric force experienced by a small

test charge placed at that point divided by the test charge itself. The direction of the electric field

is the same as the direction of the force on a positive test charge. For positive point charges, the

direction of the electric field is radially outward, and for negative point charges the direction of

the electric field is radially inward.

• Electric field lines are a means to visually represent the vector nature of electric fields. The

electric field surrounding a charge is represented by several electric field lines that extend

between charges. The electric field at any point is tangent to the electric field line at that point.

• In general, the number (density) of field lines is proportional to the magnitude of the electric

field. The presence of only few lines around a charge represents a weak electric field and the

presence of many lines represents a strong electric field.

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• The PhET simulator programs that we will use have a darker arrow to indicate a stronger electric

field and a fainter arrow to indicate a weaker electric field.

• For point charges, the magnitude of the electric field is given by:

2r

kq

q

F E

o

==

Where: E is the electric field, F is the electric force, qo is the test charge, q is the electric

charge, r is the distance from the charge, and k is Columbus constant.

Part A – Single Point Charge:

• Open the PhET Charges and Fields Simulation Software:

https://phet.colorado.edu/en/simulation/charges-and-fields

➢ In the PhET simulator check “Electric Field” and “Values” (upper right corner).

• Click and drag one “Positive” charge into the middle of the display.

• Click and drag “Voltage Sensor” into the display to measure the electric field at various

locations around the charge.

• In the below table, describe the observed electric field for the point charges.

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• Use “Clear All” icon (bottom right corner) to clear the display and repeat above procedure

using one “Negative” charge.

• Save screenshots (screen captures) of the simulation electric field for the various point charges

(total of 2 trials) and include in the graphs section of your lab report.

Part B – Two Point Charges:

• Click and drag two “Positive” charges, one near the top of the display and second near the

bottom of the display.

• Click and drag the “Voltage Sensor” into the display to measure electric field at various

locations around the charges.

• Use “Clear All” icon (bottom right corner) to clear the display and repeat the above procedure

using two “Negative” charges.

• Use “Clear All” icon (bottom right corner) to clear the display and repeat the above procedure

using an “Electric Dipole”: one positive charge and one negative charge.

• In the below table, describe the observed electric field for the various two point charges.

• Save screenshots (screen captures) of the simulation electric field for the various two point

charges (total of 3 trials) and include in the graphs section of your lab report.

Part C – Lines of Charge:

• Simulate two charged plates by creating a horizontal line of about 10 “Positive” charges on the

top of the display and a horizontal line of about 10 “Negative” charges on the middle of the

display.

• Click and drag the “Voltage Sensor” into the display to measure the electric field at various

locations between and outside the lines of charge.

• In the below table, describe the observed electric field for the two lines of charge.

• Save screenshot (screen capture) of the simulation electric field for the two lines of charge

(total of 1 trial) and include in the graphs section of your lab report.

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Part D – Electric Field Hockey:

• Open the PhET Electric Field Hockey Simulation Software, and run the browser compatible

version of this simulation:

https://phet.colorado.edu/en/simulation/legacy/electric-hockey

➢ In the PhET simulator check “Puck is Positive”, “Trace”, and “Field” (bottom of the

screen) to select a positive puck and show the path of the puck and the electric field.

➢ This PhET simulator uses point charges to move and direct a charged puck into a goal.

Click and drag charge (positive and/or negative) into the middle of the display, close to

the puck, and observe the electric fields and forces on the puck.

• Click “Start” to start moving the puck. Click “Reset” to bring the puck back to the starting

point with same charges. Click “Clear” to clear everything and start from beginning.

• Use “Practice” mode to become familiar with the simulation and testing ideas about how

charges will affect motion.

• Select Difficulty “1.” Using at most 20 positive charges and 20 negative charges direct the

charged puck into the goal without the hitting the wall. Do not let the puck go off the screen.

• When you are finished, click “Clear” and select Difficulty “2”. Using at most 20 positive

charges and 20 negative charges direct the puck to go between the two walls into the goal

without the puck hitting a wall. Do not let the puck go off the screen.

• When you are finished, click “Clear” and select Difficulty “3.” Using at most 20 positive

charges and 20 negative charges direct the puck to go between the three walls into the goal

without the puck hitting a wall. Do not let the puck go off the screen.

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• In the below table, describe for the three difficulty levels if the puck successfully entered the

goal and its path.

• Save screenshots (screen captures) showing the completed difficulty levels with the puck in

the goal, the “trace” of the puck’s path, and the electric field lines (total of 3 trials). Include in

the graphs section of your report.

Analysis:

• Part A – Single Point Charge:

1. For each trial (screenshot) explain the shape of the electric field. Discuss in your lab report.

2. What is the relation between the direction of the electric field lines and the sign of the

charges? Explain in your lab report.

3. What is the relation between the magnitude of the electric field lines and the distance to

the charges? Explain in your lab report.

• Part B – Two Point Charges:

1. For each trial (screenshot) explain the magnitude and direction of the electric field in the

different areas: close to each charge, between the two charges, and far away from the two

charges. Discuss in your lab report.

2. What happens to the electric field as the charges get closer? Explain in your lab report.

3. How do the electric fields compare for two same sign point charges and opposite sign point

charges (dipole)? Explain in your lab report.

• Part C – Lines of Charge:

1. For each trial (screenshot) explain the shape of the electric field in the different areas: close

to each line of charge, between the two lines of charges, and far away from the two lines

of charge. Discuss in your lab report.

2. Does the distance between the charge lines make a difference? Explain in your lab report.

3. Does the distance between the individual point charges that make the line of charge make

a difference? Explain in your lab report.

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• Part D – Electric Hockey:

1. For each of the difficulty levels explain why the puck follows the path that it does. Discuss

in your lab report.

2. How does the path relate to the direction of the electric field? Explain in your lab report.

3. Does the sign of the puck make a difference? Explain in your lab report.

Lab Report:

• When writing the lab report, you must review and follow very carefully the Physics Lab Report

instructions and outline document.

• In your lab report, include the Title Page, Objectives, Theory, Equipment, Data, Graphs and

Screenshots, Calculations, Conclusions, Sources of Error, and References.

• Remember to show all equations and calculations in detail and to round the results to the correct

number significant digits and precision.

• In the conclusions section, be sure to summarize the final results, comment on the agreement

or disagreement of the results with the theory or expectations, answer analysis questions, and

discuss what you personally learned from this experiment and your observations/comments.

• Remember to also answer and discuss all analysis questions in your conclusions section.

• Submit your complete lab report electronically by the due date!

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Physics - Online Lab: Electric Charges and Fields

Tables of Data and Results

• Part A – Single Point Charge:

Point Charge Electric Field Description (Magnitude and Direction)

Positive

Negative

• Part B – Two Point Charges:

Two Charge Points Electric Field Description (Magnitude and Direction)

Positive & Positive

Negative & Negative

Positive & Negative

• Part C – Lines of Charges:

Two Charge Lines Electric Field Description (Magnitude and Direction)

Positive & Negative

• Part D – Electric Field Hockey:

Difficulty Puck successful goal and path?(Explain)

1

2

3