Unit 1.1 - VoltagePower

# Unit 1.1 - VoltagePower - Basics Concepts and Laws Unit 1.1...

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1 1 Basics Concepts and Laws Unit 1.1: Voltage and Power Voltage 2 3 Voltage Energy is expended to move the charges in an electric circuit The total energy per unit of charge associated with the motion of charge between two points is called voltage . v = Δ w/ Δ q where v = the voltage in Volts w = the energy in Joules q = the charge in Coulombs 1 Volt = 1 Joule/Coulomb 4 Allesandro Volta The Volt is named after Allessandro Volta (1745-1827) who developed the electric battery (voltaic pile) in 1799. 5 Voltage Continued Voltage is also known as potential difference The voltage between two points in a circuit indicates the energy required to move charge from one point to the other An electric field is what moves the charge Does not necessarily mean that the charges are moving between these two points 6 Analogy for Voltage In a gravitational field, we speak of “up” which implies a reference and direction Voltage and gravity share the same mathematical properties You can think of voltage using a gravity analogy F g = k g m 1 m 2 r 2 F e = k e q 1 q 2 r 2

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2 7 Reference Direction for Voltage When a positive charge moves from point 1 to point 2, it sees a REDUCTION in potential of 5 V When a positive charge moves from point 2 to point 1 it sees an INCREASE in potential of 5 V. + 5 V 1 2 - 8 Voltage References Voltage requires: Definition of two points in space Reference polarity. Otherwise it is undefined and meaningless! Circuit Element v x = 3V Circuit Element + v x = 3V - 9 Voltage References Voltage is a signed quantity. Reverse the polarity Reverse the sign. The reference polarity is arbitrary. Negative voltages are OK. Circuit Element + v x = 3V - Circuit Element - v’ x = -3V + 10 Voltage References Voltage polarity may also be indicated using subscript notation The first subscript is the positive terminal The pair of subscripts define the two points in space a b Circuit Element + v ab = 3V - Circuit Element - v ba = -3V + a b v ab is the voltage at point a with respect to point b. 11
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Unit 1.1 - VoltagePower - Basics Concepts and Laws Unit 1.1...

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