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Electrostatics

Electrostatics. (Ch. 20). What is electrostatics?. 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.

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Electrostatics

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  1. Electrostatics (Ch. 20)

  2. What is electrostatics? • 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. What is charge? • 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. Opposites attract! • Positive charges like negative charges and will attract each other. • Similar charges (negative-negative and positive-positive) repel each other.

  5. Where does it come from? • Electrons! • Electrons! • 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. Quick! • 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. Quick! • How many electrons does something have if it is neutral? The same amount as the number of protons!

  8. GROUND. • 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. Quick! • What happens if a negatively charged object is grounded? • What happens if a positively charged object is grounded?

  10. How do I get some of that?! • 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. Measure! • 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: 1.602 x 10-19 C

  12. Quick! • If an object has 6.022 x 1023 more electrons than protons, what is its net charge? • 6.022x1023 electrons X 1.602x10-19 C/electron • = 96,472 C. [that’s A LOT!!] • How many electrons are there in 1 μC ? • 1x10-6C / 1.602x10-19 C/electron • = 6.24x1012 electrons. [that’s A LOT!!]

  13. Conductors vs. Insulators • 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. May the force be with you. • 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 • 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 q1q2 /r2 • k is a constant = 9.0x109 N•m2/C2

  16. Your turn to Practice • Please do Ch 20 Rev p 477 #s 1, 4, 7, 9, 14, 20, 21, 24-27.

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