电子电工技术英文课件 (4).pdf

1.3 Current,Voltage,and Power Current is associated with the flow of electric charge(like water flow).We define the current as the time rate of flow of charge.QIt=(1)where Q is charge,t is time.Voltage or potential difference is associated with the position change of electric charge.It is expressed as energy(W)divided by charge(Q).WVQ=(2)Voltage is like the water level difference created by a pump,and it is the driving force of current.Power is the time rate of change of energy.WW QPVItQ t=(3)From(2),power is also the product of voltage(like the height of waterfall)and current(like the width of waterfall).Voltage,current,and power are three important quantities which will be often used in circuit analysis.