Physics

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Lab 1: Electric Charge and Electric Interactions

Objectives In this lab you will use PhET’s simulations Balloons and Static Electricity, John Travoltage, and

Coulomb's Law to study interactions between electric charges.

Part 1: Balloons and Static Electricity Open the Balloons and Static Electricity simulation.

1. Select the option “Show all charges”.

2. Look at the balloon. What can you say about its net charge?

3. Click and drag the balloon and rub it against the sweater. What happens to the balloon?

How did the balloon get charged, with what type of charge? Where did that charge come

from?

4. What happened to the sweater? How did it get charged? Where did that charge come from?

5. Bring the balloon to the middle, between the sweater and the wall. What happens to the

balloon when you let it go? Explain the reason behind the observed phenomenon.

6. What is the overall charge of the wall? What do you expect will happen when the balloon is

brought close to the wall? Make a prediction.

7. Bring the balloon in contact with the wall. What happens to the charges in the wall? Let go

of the balloon. What happens? Explain the reason behind the observed phenomenon.

Part 2: John Travoltage Open the John Travoltage simulation.

1. Predict what will happen to John if he rubs his foot against the carpet.

2. Rub John’s foot on the carpet by clicking and dragging his foot several times. What happens?

3. Predict what will happen if John touches the doorknob.

4. Click and drag John’s hand to touch the doorknob. What happens? Explain the reason

behind the observed phenomenon.

Part 3: The Electrostatic Force – Dependence on Charge In this part use the Coulomb's Law simulation. Select the Macro Scale simulation.

1. Check the box to display Force Values.

2. Set the distance between the charges to 2 cm and set Charge 1 to 2 μC.

3. Change Charge 2 (only) and record the magnitude of the corresponding electrostatic force.

4. Complete the following table:

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𝑞2 (μC) −10 −8 −6 −4 −2 0 2 4 6 8 10

𝐹𝑒 (N)

5. Make a scatter plot of 𝐹𝑒 versus 𝑞2. Plot 𝐹𝑒 along the vertical axis and 𝑞2 along the horizontal

direction.

6. Are your results consistent with Coulomb’s law?

Part 4: The Electrostatic Force – Dependence on Distance In this part continue using the Coulomb's Law (Macro Scale) simulation.

1. Check the box to display Force Values.

2. Set each charge to 10 μC.

3. Change the distance between the charges (only) and record the magnitude of the

corresponding electrostatic force.

4. Complete the following table:

𝑟 (cm) 2 3 4 5 6 7 8 9 10

𝐹𝑒 (N)

5. Make a scatter plot of 𝐹𝑒 versus 𝑟. Plot 𝐹𝑒 along the vertical axis and 𝑟 along the horizontal

direction. Include the best-fit curve in your graph and the equation of the best-fit curve.

Decide the type of curve to fit the data with based on Coulomb’s law.