Charging by Contact Lab: FOR MARKS (25)
Due Monday, Dec. 17
Name: ____________________
Introduction:
Sometimes, when you shake hands with a friend, or touch your pet, you get an electric shock.
This happens because electric charges build up in one or both of those subjects, and then jump
from one to the other when they touch. This is called Charging by Contact.
Purpose:
In this lab, you will electrically charge objects by contact, and determine the type of charge
transferred (positive or negative).
Materials:
Pith Ball Electroscope
Acetate Strip
Polyethylene (plastic) Strip
Fur
Silk
Evaporating Dish/Support Stand
Iron strip
Glass Rod
Procedure: Read the steps CAREFULLY before you begin
1.) Charge up the Polyethylene Strip using the fur. Without allowing it to touch the pith
ball, bring the strip close to the uncharged pith ball, and then remove it. If the strip
touches the pith ball, touch the pith ball to discharge it, and try again.
a. Record your observations: (1 mark)
2.) Repeat step 1 using an Acetate strip and silk instead of Polyethylene and fur.
a. Record your observations: (1 mark)
3.) Touch the uncharged pith ball with a charged polyethylene strip, then remove the strip.
Then charge the strip again, and approach the charged pith ball, but do NOT let them
touch. Then approach the pith ball with a charged Acetate strip, and again, do NOT let
them touch. Finally, discharge the pith ball by touching it with your finger.
a. Record your observations: (1 mark)
4.) Touch the uncharged pith ball with a charged Acetate strip, then remove the strip. Then
charge the strip again, and approach the charged pith ball, but do NOT let them touch.
Then approach the pith ball with a charged Polyethylene strip, and again, do NOT let
them touch. Finally, discharge the pith ball by touching it with your finger.
a. Record your observations: (1 mark)
5.) Use the evaporating dish and modelling clay as a support stand to hold the iron strip. It
should be placed so that the iron rod is touching the pith ball. Use modelling clay to stop
the strip from sliding around.
a. Sketch this set-up below: (1 mark)
6.) Touch a charged polyethylene strip to the iron rod, on the opposite end from the pith
ball, then remove it.
a. Record your observations: (1 mark)
7.) Recharge the polyethylene strip, and bring it close to the pith ball. Then, discharge the
pith ball by touching it with your finger.
a. Record your observations: (1 mark)
8.) Repeat steps 5 – 7, but replace the iron rod with a glass rod.
a. Record your observations: (1 mark)
Questions:
1.) (2 mark) Using the Electrostatic Series (found on the back of this lab), what charge does
the Polyethylene Strip get after being rubbed with fur? What charge does the Acetate
Strip get after being rubbed with silk? (recall, the lower on the list, the better it is at
stealing electrons)
2.) (1 mark) What can you tell about the transfer of electric charge when a charged object is
placed near, but does not touch the pith ball electroscope? Explain your answer.
3.) (2 marks) Explain your answers: What can you tell about the transfer of electric charge
when the pith ball is touched by:
a. A negatively charged object
b. A positively charged object
4.) (4 marks) Write a statement explaining how charges are moving from one object to
another in steps 3 and 4. Use diagrams to help explain your answer.
5.) (1 mark) What kind of charge does the pith ball have in Step 6?
a. (1 mark) In terms of charges, explain what happened when the polyethylene
strip touched the iron rod in Step 6.
6.) (1 mark) What kind of charge does the pith ball have in Step 8?
a. (1 marks) In terms of charges, explain what happened when the polyethylene
strip touched the iron rod in Step 6.
7.) (1 marks) Describe the difference in how charges move through a glass rod as compared
to an iron rod.
8.) (3 marks) Imagine you have two pith ball electroscopes. Predict and explain what
happens when the pith balls are brought close together if:
a. They both have the same charge.
b. They have opposite charges.
c. One is charged and the other is not.
Electrostatic Series
Acetate
Weak Hold on Electrons
Glass
Wool
Fur, Human Hair
Calcium, Magnesium, Lead
Silk
Aluminum, Zinc
Cotton
Paraffin Wax
Ebonite
Polyethylene (plastic)
Carbon, Copper, Nickel
Rubber
Sulphur
Platinum, Gold
Strong Hold on Electrons