SNC1P – Lesson 1: Electricity
One of the most common effects of static electricity occurs when you comb your hair on a day when
the air is very dry. Your hair stands on end, and there may be a crackling noise. Static electricity
causes clothes to cling together in the dryer. If, on a dry winter day, you take off an acrylic sweater
that has been work over a woollen shirt, you can hear, and sometimes even see, the discharges of builtup electricity. You can also sense and hear its effects if you move your hand lightly over the surface of
a television or computer screen, after it has been on for a while.
The Electrical Nature of Matter (Review from Chemistry)
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All matter is made up of atoms. An atom is made up of a positively charged nucleus in the
middle (containing positive protons and neutral neutrons), surrounded by tiny, negatively
charged electrons.
First Instruction: Draw a Bohr-Rutherford Model of Helium, and label the protons (+),
neutrons(o) and electrons(-).
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Atoms become charges when they gain or lose electrons.
Electric Charge
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There are two kinds of electric charge: negative and positive.
When two different neutral substances are rubbed together, one substance always becomes
negatively charged while the other one becomes positively charges.
Example: when a comb is rubbed with a wool, the comb acquires a negative charge, while the
wool acquires a positive charge
On many common substances the electric charge remains “static”: in other words, the charge
stays where the rubbing action occurred on each of the charged objects.
Static electric charge refers to electric charges that are stationary or at rest; the study of static
electric charge is called electrostatics.
The Law of Electric Charges
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States that like charges repel one another
Unlike charges attract each other.
Charged objects can attract neutral objects
Conductors
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Conductors, such as metals, are substances that allow charges to move freely through the object;
the electrons from individuals atoms easily flow from one atom to another and do not stay in
place
For this reason, electric charges do not collect on the surface of metals
Insulators
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Insulators, such as non-metals, are substances that do not allow charges to move freely through
the object; the electrons tend to stay around individual atoms and do not flow from one atom to
another.
Second Instruction: Using your Periodic Table from Chemistry (or the back of your textbook)
list 3 metals (good conductors) and 3 non-metals (insulators)
Metals (Good Conductors):
________________________, ________________________, ____________________________
Non-Metals (Insulators)
____________________________, _________________________, ___________________________
Charging By Friction
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Neutral objects have equal numbers of electrons and protons.
When two insulators, such as a comb and a piece of wool cloth, are rubbed together, the friction
can cause electrons to get knocked off one material and transferred to the other material.
Because one object now has more electrons than protons, it is negatively charged. The other
object, having lost electrons, becomes positively charged.
The Electrostatic Series
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A list developed by scientists to determine the kind of electric
charge produced on each substance when any two substances
are rubbed together.
When charging by friction occurs, the substance higher n the
list always loses electrons and becomes positively charged,
while the substance lower in the list gains those same
electrons and becomes negatively charged.
Learning Check Questions
1. Given the electrostatic series, on the previous page, determine the charge (positive or negative)
after the following two objects are rubbed together.
a. Plastic wrap and cat fur
Plastic wrap _______________ charge. Cat fur _____________________ charge
b. Silk and wood
Silk __________________ charge. Wood ___________________ charge
2. Explain why electrical insulators are used to cover the conduction wires in electrical cords
attached to appliances.
Charge by Contact
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Charging by contacts involves a charged object making direct contact with a neutral object.
If the charged object is negative, electrons can flow into the neutral object resulting in the
object acquiring a negative charge. Although the originally negatively charged object loses
some of its negative charge, it still is negative. The originally charged object and the newly
charges object will repel one another because they have the same charge.
If the charged object in positive, it is the neutral object that loses electrons to the positively
charged object. Since the neutral object loses negative charge, it acquires a positive charge.
The originally charged object ends up with slightly less positive charge that what was originally
had. The originally charged object and the newly charged object will repel one another because
they have the same charge.
Learning Check Questions
1. What are the two kinds of electrical charge?
2. State the three points of the law of electrical charges.
3. What are the names of two methods of charging neutral objects?
4. Describe the difference between insulator and conductor