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:
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.
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.
Positive charges like negative charges and will attract each other. Similar charges (negative-negative and positive-positive) repel each other.
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.
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.
How many electrons does something have if it is neutral? The same amount as the number of protons!
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.
What happens if a negatively charged object is grounded? What happens if a positively charged object is grounded?
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)
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
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!!]
Conductors allow electrons to move about freely. Metal. Graphite. Water. Insulators do not allow electrons to move about freely. Plastic. Rubber. Glass. Cloth. Wood.
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!)
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
Please do Ch 20 Rev p 477 #s 1, 4, 7, 9, 14, 20, 21,