Voltage, Current, Charge and Energy Introduction Voltage, Current, Charge and Energy (Sections 1.3 – 1.5)

Voltage, Current Charge and Energy Consider potential energy of a mass held at a height m h g E = m g h Notice that height is a double-ended measurement It is the distance between two points We say it is an across variable 11/16/2018 Voltage, Current Charge and Energy

Galileo & the Falling Bodies Experiment

Same two masses Different place speed time energy

Mass and place are separable E = m x g h Together represent place gh represents the mechanical potential of a location independent of the mass for example, the top of Prescott St. We may write gh = E / m Or even gh = dE / dm

The fundamental equation of gravity Gravity is the property that defines mass F = G m1 m2 r2 All our other equations derive from this one The fundamental equation of electricity Electricity is the property that defines charge F = k q1 q2 r2 The equations are virtually identical!

The mechanical equivalent is the flow of mass Voltage and Current Voltage is the electrical equivalent of mechanical potential It represents an electrical hill v = dw dq We get potential energy by placing some quantity of charge on top of the hill v = voltage in volts w = energy in joules q = charge in coulombs i = current in amperes t = time in seconds In circuits we also pay attention to the current - the amount of charge that flows per unit time i = dq dt The mechanical equivalent is the flow of mass

Voltage is an across measurement It’s our electrical hill h Height is measured as the difference between its top and its bottom Current is a through measurement It flows through a wire Like water flows through a pipe

An ideal electrical component v + - i 1 2 It represents positive charge flowing from terminal 1 to terminal 2 If i is positive It represents positive charge flowing from terminal 2 to terminal 1 If i is negative It is the voltage drop from terminal 1 to terminal 2 It is the voltage rise from terminal 2 to terminal 1 If v is positive or It is the voltage rise from terminal 1 to terminal 2 It is the voltage drop from terminal 2 to terminal 1 If v is negative or