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(Ch. 20).  The study of STATIC ELECTRICITY.  Static electricity is electrical charges that can be collected and/or held in one place.  This is different.

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Presentation on theme: "(Ch. 20).  The study of STATIC ELECTRICITY.  Static electricity is electrical charges that can be collected and/or held in one place.  This is different."— Presentation transcript:

1 (Ch. 20)

2  The study of STATIC ELECTRICITY.  Static electricity is electrical charges that can be collected and/or held in one place.  This is different from current electricity which is what powers your refrigerator, lights, batteries, etc.

3  Charge is divided into two categories: positive and negative charges.  Something is said to be charged when it has an unequal amount of positive/negative charges.  If there are more positive charges, it is positively charged.  If there are more negative charges, it is negatively charged.  If there are the same amount, it is said to be neutral.

4  Positive charges like negative charges and will attract each other.  Similar charges (negative-negative and positive-positive) repel each other.

5  Electrons!  Only electrons move around from one object to another to charge objects. (Why is that?) Just like heat, electrons move from high concentration to low concentration.

6  What happens if a positively charged object touches a negatively charged object? Electrons flow from negatively charged object  positive charged object until they are both neutral.

7  How many electrons does something have if it is neutral? The same amount as the number of protons!

8  In electricity the “ground” is very important. This is generally a huge body that will be electrically neutral.  The Earth is a great example of “ground.” The human body can also serve as a ground for many cases.  Example: By touching the charged object, you ground it.

9  What happens if a negatively charged object is grounded?  What happens if a positively charged object is grounded?

10  THREE WAYS TO OBTAIN CHARGE:  Conduction (two object directly touch)  Induction (bringing a charged object near a neutral object will induce a charge in the neutral object).  Friction (rubbing electrons onto something)

11  The SI unit for charge is the Coulomb. It is abbreviated with a C.  Examples:  1.0 C  3.5 μC  6.3 nC  The charge of 1 electron (called the elementary charge) is: x C

12  If an object has x more electrons than protons, what is its net charge? 6.022x10 23 electrons X 1.602x C/electron = 96,472 C. [that’s A LOT!!]  How many electrons are there in 1 μC ? 1x10 -6 C / 1.602x C/electron = 6.24x10 12 electrons. [that’s A LOT!!]

13  Conductors allow electrons to move about freely.  Metal. Graphite. Water.  Insulators do not allow electrons to move about freely.  Plastic. Rubber. Glass. Cloth. Wood.

14  Like charges repel. Opposites attract.  The attraction and repulsion is a FORCE.  Electric force is a non-contact force.  (like gravitation!)  Electric force in an inverse square law.  (like gravitation!)

15  Coulomb’s law:  The force between two charges is proportional to the magnitude of the two charges and inversely proportional to the square of the distance between the two.  F = k q 1 q 2 /r 2  k is a constant = 9.0x10 9 N m 2 /C 2

16  Please do Ch 20 Rev p 477 #s 1, 4, 7, 9, 14, 20, 21,


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