SNC1D - Static Electricity
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Charging By Contact
Remember that when charging by friction both
objects start with a neutral charge and end with
opposite charges. After friction the oppositely
charged objects attract each other.
When charging by contact one object starts with a
positive or negative charge and the other object
starts with a neutral charge. Then the positively or
negatively charged object contacts the neutral object.
The electrons are equally shared between both
objects. After contact both objects will end up with
the same charge. Then both objects will repel each
other.
SNC1D - Static Electricity
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Ex. 1 A positively charged object contacts a neutral object
Draw BEFORE CONTACT between a positively
charged wool sweater and a neutral cat.
Positive wool
8+ 4 -
Neutral cat
8+ 8-
Charging by Contact - Electrons shared equally
_________________________
___________________________
________________________
___________________________
SNC1D - Static Electricity
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Ex.2: A negative object contacts a neutral object
Draw BEFORE CONTACT between a negatively
charged rubber boot and neutral cotton.
Negative rubber
Neutral cotton
8+ 12 -
8+ 8-
Charging by Contact - Electrons shared equally
__________________
__________________
_______________
_______________
SNC1D - Static Electricity
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Charging By Contact
Remember that when charging by _____________ both objects ______________
______________________________ and __________________________________. After friction
the oppositely charged objects _________________ each other.
When charging by contact _______________________________________________
_____________________________________________________________________. Then the
positively or negatively charged object contacts the neutral object. The electrons are
_________________________________________________ between both objects.
________________ contact ___________________________________ ________________. Then
both objects will _________________ each other.
Example 1: A positive object contacts a neutral object
Draw BEFORE CONTACT between a positively charged wool sweater and a neutral cat.
Charging by Contact – Electrons shared equally
SNC1D - Static Electricity
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Example 2: A negative object contacts a neutral object
Draw BEFORE CONTACT between a negatively charged rubber boot and neutral cotton
Charging by Contact – Electrons shared equally
.
SNC1D - Static Electricity
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Charging by Contact Practice problems
Problem 1: A positively charged glass rod comes in contact with a neutral piece of wax. Draw
before and after electrostatic diagrams showing the charges and the final charge on the objects.
Charging by Contact
Problem 2: A neutral platinum ring comes in contact with a negatively charged balloon. Draw
before and after diagrams showing the charges and the final charge on the objects.
Charging by Contact
Homework: Read the lab description and look at the picture on p 276 to learn about a pith ball.
Read Nelson p 278-279. Do p 279 #1-4
SNC1D - Static Electricity
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Homework Questions – Nelson p. 279 (Read Nelson pp 278-279)
1. What happens when a negatively charged object touches an uncharged pith ball on an
electroscope? Use a diagram to explain your answer.
2. When an object is charged by contact, what kind of charge does the object have compared with
that on the object giving the charge? Explain in terms of the model for the electrical nature of
matter (i.e.in terms of protons and electrons, and the movement of charges).
3. Why does a spark occur when a person who is charged touches an uncharged object? Would
moving the hand to the doorknob very fast prevent the spark from occurring?
4. If a cat was combed with an ebonite comb, and someone else touched the cat, what charge
would that person receive from the cat’s fur. (See Table 1 on page 275 – the Electrostatic
Series). Explain your answer.