Lab 1 - Have fun PDF

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Lab 1 Electric Charge and Electric Field

Part I Electric Charge Open the Balloons and Static Electricity simulation. The simulation “Balloons and Static Electricity” can be run online (chose “Run now”). Once your application has started, click “Reset All”. Make sure that only the “show all charges” and “wall” buttons are selected. Once your application has started, click “Reset All”. Make sure that only the “show all charges” and “wall” buttons are selected. 1.

Look at the balloon. What can you say about its charge? (Hint: count both types of charges) The balloon’s number of protons and electrons are equal, so it doesn’t have a positive or negative charge because they cancel each other out

2. Click and drag the balloon and rub it against the sweater. What happens to the balloon? The electrons from the sweater are attracted to the balloon so the balloon has a strong negative charge after it rubs on the sweater 3. How did the balloon get charged, with what type of charge? The balloon got charged by the electrons from the sweater transferring to the balloon, so the balloon is now negatively charge 4. Where did that charge come from? The sweater’s electrons 5. What happened to the sweater? How did it get charged? The sweater lost it’s electrons to the balloon, leaving only protons and therefore only a positive charge on it 6. Bring the balloon in the middle, between the sweater and the wall. What happens to the balloon when you let it go? Explain. The balloon is attracted to the sweater because the sweater is now positively charged and the balloon is now negatively charged, so it sticks to the sweater 7. What is the overall charge of the wall? Neutral 8. What do you think will happen when the balloon is brought close to the wall? Predict first.

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The electrons inside the balloon will repel the electrons inside the wall, while the protons will attract it 9. Bring the balloon in contact with the wall. What happens to the charges in the wall? The protons remain the same, but the electrons are repelled by the balloon’s electrons 10. Let go of the balloon. What happens? Explain. The protons in the wall give out a small attraction to the balloon, so when the distance between the balloon and wall is small the balloon sticks to the wall. But overall the attraction to the sweater is much stronger so the balloon normally goes to the sweater

Part II Electric Field from Two Point Charges Open the two charges simulation, recall that both charges produce electric field around. The simulation shows three regions. 1. From what you learned, at which region (I, II or III) do you think the total electric field is zero? Region II 2. Now click on region I, as you move the point location closer to the charges, do you see two vectors? They are the electric field vectors from the two charges. a) Which one is bigger? +3Q b) Are they in the same direction? No c) As you move from a closer point to further away from both charges, what happens to both of them? They both become smaller d) Will they ever cancel each other? Eventually yes 3. Now click on region II, move the point in region II a) Are the two fields in the same direction? Yes b) Can the blue one bigger than the red one? Yes when it’s closer to the point charge 4. Click on region III a) Are they in the same direction? Page 2 of 4

No b) Can you find a location where they cancel each other? Yes

5. Click on the Calculate button, calculate x, where the electric field is zero. 4.5? 6. Click on the Test charge button and put the test charge at the location you just calculated in step 5 to see if your calculation is correct. It wasn’t

Part III Electric Field Open the Field and String simulation Record and calculate the following: a) Is this an evenly distributed electric Field? How do you know?

No because the ball isn’t hanging neutrally, it’s being pulled to a side b) Use the slide bar for Electric Field to change the electric field to Minimum Electric Field, record the value: 10.1 N/C

c) Now slide bar to increase the electric field, state the relationship between the line density and electric field. As the electric field increases the lines become more dense

d) What happens to the charged ball on the string as you increased electric field? Describe why? It’s pulled more and more because more electric field lines appear and increase the power of the field

e) Leave the electric field bar to 20N/C, what else can you do to change the swing angle of the charged ball? Try it out. Page 3 of 4

If I change the charge of the ball to neutral or negative, it either hangs still or swings the opposite direction If I increase the mass of the ball it becomes heavier and therefore harder to move, so its swing decreases f) Keep the charge at 10.0 microC and mass at 20 milligrams, Name the forces on the charged ball? What is the total net force? The forces are tension, the electric field, and weight/gravity, and the total net force is 0 because the ball is moving at a constant velocity of 0

g) Use the free-body diagram given on the simulation, find value of all three forces.

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