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

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Presentation on theme: "Electrostatics Ancient Greeks were familiar with electrostatic phenomenon. A piece of amber rubbed with fur could attract small objects over a distance."— Presentation transcript:

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

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

5 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.

6 Charges Like charges repel.Unlike charges attract.

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

8 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. positivenegative neutral

9 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.

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

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

12 Electrostatic Forces Coulombs Law Like charges repel.Unlike charges attract. F = Kq 1 q 2 r 2

13 Coulomb’s Law: force between two charged particles K = 9 x 10 9 Nm 2 /C 2 (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. F = Kq 1 q 2 r 2

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

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

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

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

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

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

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


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