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# SC PHYS 202 - Circuits and electric flow

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PHYS 202 1st Edition Lecture 7 Outline of Last Lecture I. Review for exam oneOutline of Current Lecture II. Conductors ReviewIII. Equi-potentialIV. Electric Circuitsa. Currentb. ResistanceCurrent LectureConductor Review:A conductor is a medium in which charges are able to move about freely. Since they are free to move, they go as far as they can, which would be on the surface of the conductor. This means that the electric field inside the conductor will be equal to zero. Remember that E=ΔV/Δr. So, if E is 0 within a conductor(as it should be), then Vis the same at all points, meaning that there is no change (Δ) in V. Equi-potential:Imagine a smooth hill. If there is water at the top of this hill, it will flow all the way down the hill until all of the water is level at the bottom. A similar concept exists for the flow of a charge. If a charge is placed in a region that has a higher potential, the charge will flow from the area of higher potential to an area of lower potential, until there is no difference in potential(V) in that area. Therefore, electric potential on a conductor is constant. A surface with this constant potential, such as a conductor, is called an “equi-potential surface”.U vs. VU measures the electrical potential energy that transpires between two point charges. V measures the electric potential due to a point charge. This means that U measures electric potential as it works it a system, whereas V measures the electric potential focused in a certain area. Electric Circuits:Circuit is a series that allows electricity to flow through it. A circuit is usually made up of a set of conducting wires connected to a power source (symbolized with in a diagram) such as a battery, and a resistor of some kind (symbolized in a diagram as /\/\/\ ) /\/\/\/\These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Current:Electric current describes the flow of a charge in motion. Current(i) through a circuit can be described as the change in charge over the change in time. This is represented in the equation;i=Δq/Δt The unit for electric current is C/S or Ampere(A)Resistance:Every conductor poses some kind of resistance to charge. The resistance of a conductor is dependent on the material of that conductor, the length of the conductor, and it’s cross sectional area. The larger the cross section area, the smaller the resistance, and the longer the conductor, the grater the resistance. Resistance can be represented by the equation;R= ϱL/AWhere L is the length, A is the cross sectional area(like the size of the hole through a straw), and ϱ is set value called resistivity. Resistivity is based on the material that the conductor is made out of, and is ultimately a measure of hour resistive that particular material is to a charge flowing through it.Resistance(R) of a circuit is also equal to the electric potential(V) divided by the current(i). The equation for thisisR=V/iThis equation is known as Ohms rule(not law because it is an approximation), and as such, the unit for resistance is

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