Exploring electric charges
PURPOSE: USE SIMULATIONS TO EXPLORE ELECTROSTATIC INTERACTIONS
In this online lab you will use simulations to check your knowledge regarding electrostatic interactions.
Balloons and Static Electricity Simulation
To interactively explore some of the concepts you have learned so far please go to :
(http://phet.colorado.edu). Choose “play with sims”. On new page, type in “static electricity” in the
search box. We will start with the Balloons and Static Electricity simulation and the John Travoltage
simulation.
The image on the webpage should look like the
one on the left.
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.
1) Look at the balloon. What can you say about its charge? (Hint: count both types of charges)
Neutral, the number of positive equals number of negative.
2) Click and drag the balloon and rub it against the sweater. What happens to the balloon?
The balloon takes the negative charges from the sweater.
3) How did the balloon get charged, with what type of charge?
Rubbing the balloon against the sweater causes the balloon to be charged negative. This is
charging by friction.
4) Where did that charge come from?
Charge is negative from the electrons.
5) What happened to the sweater? How did it get charged?
The sweater lost electrons so it got charged positive.
6) Bring the balloon in the middle, between the sweater and the wall. What happens to the balloon
when you let it go? Explain.
When the balloon is released, it is attracted towards the sweater because the positive sweater
attracts the negatively charged balloon. Unlike charges attract.
7) What is the overall charge of the wall?
The charge of the wall is neutral. Number of positives equal number of negatives.
8) What do you think will happen when the balloon is brought close to the wall? Predict first.
The balloon will stick to the wall.
9) Bring the balloon in contact with the wall. What happens to the charges in the wall?
The negative charges on the wall move further away and the balloon is attracted to the wall
causing it to stick.
10) Let go of the balloon. What happens? Explain.
As the negative balloon is brought near. The positive charges stay in place in the wall and are
attracted to the negative balloon.
11) Click the “Reset All” button. Select “show all charges”, and “Two balloons”. What can you tell
about the overall charge of all the objects in your simulation window?
All the objects have equal number of positive and negative charges and are charged neutral.
12) Select “Show charge differences”. Rub each balloon against the sweater. What happens to each
one of them?
As each balloon is rubbed against the sweater, each of them take some of the negative charge of
the sweater causing them to be charged negative. The sweater become positive.
13) Why are the two balloons stuck on the sweater?
Positives attract negative.
14) Try to get one balloon off the sweater by using the other balloon. Can you do it? If yes, explain
why this is possible.
It is possible to repel one balloon with the other because both balloons are charged negative.
Like charges repel.
Go back to your web browser window and select “John Travoltage”.
1) Predict what will happen to John if he rubs his foot against the carpet.
As you rub the foot on the carpet, charge builds up in the body.
2) Rub John’s foot on the carpet by clicking and dragging his foot few times. What happens?
Charge continues to build up in the body.
3) Predict what will happen if John touches the door knob.
As the finger is brought near the door knob, the person will get a shock.
4) Click and drag John’s hand such that it touched the doorknob. What happened?
As the finger is brought near the door knob, a flow of electrons rushes out of the body causing a
shock.
5) What would you call what happened to John?
The flow of electrons between the objects is causing the body to discharge.
6) When John Travoltage’s hand is turned away from the knob, no spark will start. But in step 4, you
sustained a spark from that configuration. a) What does this say about the conductivity of air?
Air acts as an insulator preventing discharge between objects.
b) How can you get maximum charge built up on John Travoltage without producing a spark?
Maximum charge builds up when foot is rubbed against carpet and hand is away from the door
knob.
c) Under what circumstances – if any – will a spark jump from John Travoltage’s foot to the
doorknob? Why do you suppose this is (in terms of science involved)?
When the buildup of charge is so great to overcome the insulation of the air, the electrons will
jump across to partially discharge from the object.
d) Produce the longest spark possible: the spark is between John’s hand pointing away from the
knob and the doorknob, itself. How did you do it (hand position)?
To get the longest spark, the hand is pointed away from the doorknob and the foot is rubbed
against the carpet a long time.
e) Sustain the longest spark possible. How did you do it (hand position)?
To get the longest spark, the hand is pointed straight up towards the bookshelf.
7) How is this different from the balloon and sweater or balloon and wall touching each other?
When working with balloons, the charge build up wasn’t large enough to cause a discharge
(spark). It was simply charges at rest attracting or repelling each object.