Current

Moving Charge  A charge in an electric field is subject to a force. Acceleration  Positive charges move with the field.  Negative charges move against the field.   E

Water Flow  Moving water in a pipe forms a current. Steady flow at constant velocity  The mass flow is the density times velocity times area.  Pressure provides the force. v A 

Charge Flow  Moving charge forms a current. Charge density ne instead of mass density  The charge flow is the density times velocity times area. Defined for positive charge  Potential provides the force. v A ne 

Current Direction  In a conductors electrons are free to move. Collide with other chargesCollide with other charges Random motionRandom motion  A potential along a wire causes a net velocity for electrons. Negative charge moves opposite to currentNegative charge moves opposite to current

Ampere  Current is the average amount of charge flowing through an area in a unit of time.  The unit of electric current is the ampere (A). 1 A = 1 C/s1 A = 1 C/s  The ampere is a fundamental unit of the SI. Coulomb is derived from itCoulomb is derived from it 1 C = 1 A s1 C = 1 A s

Electron Beam  The current comes from the definition. I =  q/  t (3.20 x C)/(200 x s) I =  A (negative beam)  The charge of one electron is used to get the number rate. (-1.60 x )/(-1.60 x )  e/  t = 1.00 x electrons/s  In an electron microscope a constant electron beam transports 3.20  C of electrons in 200 ms across a vacuum.  Find the current and number of electrons per second. next