# Phet: Physics Web Search: Electricity & Magnetism

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Phet: Physics Web Search: Electric Charge Basics

Name______Date ______Period ______

Visit Teacher Webpage Introduction to Physics- to find Links to Phet Interactive Simulations.

Part I:

1. On the left side of your teacher’s Webpage find the “Phet: Electricity Interactive Simulations” Page
2. Open “Balloons” – (like the image to the left)
3. Check “Show all Charges.” Nothing else should be checked.
4. Rub the balloon on the shirt
5. What overall charge does the balloon now have? ______
6. What overall charge does the shirt now have? ______
1. What happens when you drag the balloon away from the shirt and let it go? ______
2. Why? ______
3. Reset
4. Check “Wall”
5. Rub the balloon on the shirt again.
6. What happens to the negative charges in the wall when you move the balloon near it? ______
7. What happens to the positive charges in the wall when you move the balloon near it? ______
8. Why don’t all the positive charges move toward the balloon? ______
1. Hold the balloon in between the wall and shirt and release it
2. Why doesn’t the balloon just stay in the middle? (hint: the number of protons minus the number of electrons = the net charge of the object______

Part II :

1. Open “Travoltage” Page down to find the image to the left.
2. Experiment with rubbing Travolta’s foot against the carpet and touching his finger to the door handle.
3. What do the little blue circles represent? ______
4. What is the relationship between Travolta’s net charge and how many times you rub his foot onto the carpet?______
5. Now try building up charge while his finger is on the door.
6. What happens? ______
7. Try rubbing his foot on the door and behind him in the air.
8. What happens? ______
9. Why? ______
10. Move his finger away again and build up another charge
11. When Travolta’s finger is near the door knob, what happens to the electrons currently in the metal door knob? ______
12. How can you get the maximum charge built up on John Travoltage without producing a spark?______
1. Under what circumstances—if any—will a spark jump from John Travoltage’s foot to thedoorknob? Why do you suppose this is (in terms of the physics involved)?
1. Rotate John Travoltage’s arm so that his finger is pointing directly at the doorknob. Carefully rub

his foot against the carpet without producing a spark.What is the greatest number of charges you can get

onto John Travoltage’s body? (How manysmall spherical charges can be collected on his body before a

discharge occurs?)______

1. Produce the longest spark (distance between finger and knob) possible: the spark is between John’s hand pointing directly away from the knob and the doorknob, itself. (Hint: The correct procedure requires less than a minute to complete.)

How did you do it?______

1. Sustain the longest spark possible. Now that you know how to initiate the longest spark, determine a method to sustain the spark for several seconds (at least 10 seconds). How did you do it?
1. Consider two variable quantities: the amount of charge Q on John Travoltage’s body and thedistance d from his finger to the doorknob. How do these quantities relate to the likelihood S of aspark jumping?

Select the best equation to represent this relationship. (This is a rough approximation, not an exact equation.)

___ S ~ Qd ___ S ~ Q/d ___S ~ d/Q ___ S ~ 1/(Qd)

1. Write a statement that conveys what your expression in question 17 means.
1. When John Travoltage’s hand is turned away from the knob, no spark will start. But in Step 16,

you sustained a spark from that configuration. What does this say about the conductivity of air?

1. Why are shocks worse when you touch conductors rather than insulators? ______
2. If you take your hat off on a dry winter day, sometimes your hair will stand up. Explain this phenomenon. ______

Part III:

Software

In Electric Field Hockey, a player guides a charged puck into the goal (bracket). The player muststrategically place positive and negative charges on the “rink” so that when the puck is released, itwill be propelled by electric forces into the goal. Clicking the on‐screen “Start” button sets the puckfree. The charges placed on the rink are fixed in place and will not move.

1. Open “Electric Hockey” Look for the image to the left.
2. How can you set up just one negative charge to score a goal? (Remember to hit start) ______
3. Clear each time you try a new set up. Reset if you want to retry your current set up.
4. How can you set up just one positive charge to score a goal? ______
5. Using the positive and negative charge to move your puck. Change the mass and see what happens.
6. What happens when the mass is lighter? ______
7. Why does the mass affect the speed if it is not apart of the electric force equation? Hint: Remember Newton’s second Law? ______

Discussion

In the space around a charged object is an “aura” generally described as an electric field. The electric

field is a vector quantity, so the fields charges add vectorially. If they have the samedirection, the fields add (Figure 1.a) and if they have opposite directions, they subtract, and may evencancel each other (Figure 1.b). And if the directions are at angles to each other, their effects combineand act at a new angle (Figure 1.c).

1. Reset – Put one positive charge on the surface and one negative charge directly below it.
2. Check the “Field” box.
3. Draw the field (you can connect the arrows if you wish)
1. Set up a triangle of charges, with two positives and one negative. Draw the field lines for this set up. Think critically why the field lines behave this way.
1. Play around with positively and negatively charged particles. Change the number of the particles and change the distances between them. What do you observe about the electric field lines? Record 3 of your most critical observations and draw one that you find to be the most intriguing to you.
1. Now play the game. Set the mass slider control to 100. (Doing so makes it easier to follow the action on the screen.)Place your three charged pucks in a position so you may score. You can practice a little bit if you want.
2. Reset: Using your three pucks play the game. Set difficulty to 1, then 2, then 3. When you beat each level, draw your set up, to show me your winning moves. Hint: leaving the field box checked might help you
1. Level 1 set up:
1. Level 2 set up:
1. Level 3 set up: