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Presentation on theme: "Electricity."— Presentation transcript:

1 Electricity

2 Electrostatics Ancient Greeks were familiar with electrostatic phenomenon. A piece of amber rubbed with fur could attract small objects over a distance.

3 Think What is another force that acts over a distance?

4 Electric Nature of Matter
Atoms are made of protons and electrons. Electrons (negative charge) are free to move, while protons (positive charge) are not as free to move. Matter usually has a balanced charge.

5 Charges Like charges repel. Unlike charges attract.

6 Static Electricity: Definition
An imbalance of charge. Usually it is the electrons that move.

7 Mechanisms of Charge Imbalance
Contact/Peeling: Rub balloon on hair. Conduction: Touch a charged object to a neutral object. Induction: Bring a charged object close to a neutral object. positive negative neutral

8 Van de Graff Generator Like amber and fur, a rubber belt transfers charge from a wool roller to the dome. The charge builds up and is distributed on the surface of the sphere.

9 Electrostatic Forces Like charges repel. Unlike charges attract. We have seen that electric charges exert forces on other electric charges.

10 Think-Partner-Share What factors might affect the magnitude of this electrostatic force?

11 Electrostatic Forces F = Kq1q2 r2 Coulombs Law Like charges repel.
Unlike charges attract. Coulombs Law F = Kq1q2 r2

12 Coulomb’s Law: force between two charged particles
F = Kq1q2 r2 K = 9 x 109 Nm2/C2 (electrostatic constant) q = value of charge in Coulombs A comb has a charge of about 1 microcoulomb (10-6 C) r = distance between charges. Note the inverse square relationship.

13 Think What is another inverse square relationships we have seen?

14 Electric Field "An electric field is a region in which charged particles experience a force" ELECTRIC FIELD +q FORCE FORCE -q Lines of force show the direction of the force felt by a positive charge

15 Field Lines - Field Lines start and end on charges.
+ Field Lines start and end on charges. The density of field lines is a measure of the strength of the field.

+q IT IS A VECTOR ELECTRIC FIELD STRENGTH E This is defined as the force per unit charge acting at a point in the field.             UNITS = N/C Hence the force on a charge of q coulombs in the diagram above is given by : F = E q

17 Motion of Charge Initially Moving Perpendicularly to an Electric Field e.g. an electron in an oscilloscope beam. y E x vH -- VH is the initial horizontal velocity and REMAINS CONSTANT - Like a projectile !! For the vertical motion u = 0, so where m = mass of the particle and F = Eq For the horizontal motion, x = VH t which is a PARABOLA Hence

18 What is electricity? The interaction between charged particles of matter. We discussed “static” electricity or charge imbalance – how about if charges are moving?

19 Current Electricity Current = flow of charge, such as electrons through a wire in a circuit.

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