Loo Ow (think Hawaii) Two metal spheres, A and B, possess charges of 1.0 microcoulomb and 2.0 microcoulombs, respectively. In the diagram below, arrow F represents the electrostatic force exerted on sphere B by sphere A. Draw the magnitude and direction of the electrostatic force exerted on sphere A by sphere B

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Objectives What is Voltage?

Homework- Finish Worksheet (yes on the weekend – we are a week behind – I was thinking of giving the test on the weekend!)

End of PRACTICE

Storing Electrical Energy Electrical Potential (Voltage)

To increase PE ++ To decrease PE + - Electrical PE

Calculating Potential Difference Amount of potential difference: WORK DONE PER UNIT CHARGE 1 VOLT = 1 J/C

6.0 joules of work are done in pushing an object with +3.0 coulombs of charge toward a charged plate. –What type of charge does the plate have on it? –How much potential energy was stored in the electric fields? –How much electrical potential was generated? Positive Example #1 6.0 J V = W/q V = 6.0 J / 3.0 C V = 2.0 V

An object with a 2.0 coulomb charge is accelerated through a potential difference of 10 volts. –How much kinetic energy does the object gain? Example #2 V = W/q W = Vq W = (10 V)(2.0 C) = 20 J

What is Voltage? In electrical fields, we will want to think in terms of the potential energy per unit of charge. Near the earth's surface the potential energy of a mass, m, h meters above the surface is mgh. The potential energy per unit mass is just gh. Voltage is the potential energy per unit charge for a charge in an electrical force field.

Those wacky scientists… Some scientists work with electrons and protons all day long. Rather than using numbers like 4.8 x all day, they have an easier way to think about things. It might not always be easier for us.

Electron-volts Alternate unit for work/energy: Raises 1e to an electrical potential of 1 V 1 eV = 1.6 x J What is the energy needed to raise two electrons to a potential of 1.0 volt? V = W /q 1.0 V = W / 2e W = 2.0eV What is the energy needed to raise four electrons to a potential of 2.5 volts? V = W /q 2.5 V = W / 4e W = 10 eV

An electron travels a distance of 2.0 x meter as its electrical potential is raised by 300 volts. –How much work is done on the electron? Example #3 V = W/q 300 V = W / 1e W = 300 eV V = W/q 300 V = W / 1.6 x C W = 4.8 x J

End of PRACTICE

Lab # Electrostatic Cycle