PH 105 Dr. Cecilia Vogel Lecture 21

OUTLINE  Electricity  Magnetism  E & M  Electronic circuits  Circuit elements

Electricity  Electricity is the force that effects ______________:  Makes electrons flow as current in wires.  Makes clothes cling together in laundry  Makes strands of hair push away from each other  so hair stands on end.  etc  Like charges _________  Opposite charges ________

Magnetism  Magnetism is the force that effects __________  Makes compasses point North.  Makes magnets cling to fridge.  Tells certain worms which way is down, so they can burrow in muck.  etc.  Like poles ________  Opposite poles ________

E & M  Magnetism also affects moving charges:  Moving charges act like magnets.  Current flowing around in a coil of wire  acts just like a  Right hand rule:  Wrap your right-hand fingers around the coil,  pointing in the direction the current is flowing.  then your thumb points out the north magnetic pole

E & M  Moving magnets also affect charges:  If a magnet moves near a coil  it will induce current to flow in the coil.  If magnetism changes,  current will resist or oppose change.  So if you try to change the current flowing thru a coil,  you will meet with

Current Events  If current is to flow, we need 3 things   such as a battery or electric outlet.  voltage provides the force that makes electrons move.   such as a wire  electrons in a conductor are free to move.  and

Electric Circuit  In a circuit,  there is a complete loop for electrons to flow around.  maybe more than one  Current never flows away from a battery and disappears.  Current never shows up out of nowhere at the battery.  Whatever flows out of one terminal of battery, flows back in the other.

AC/DC  Direct Current (DC)  is current that flows always in the __________  like from the + to the - terminal of a battery.  Alternating Current (AC)  flows in one direction, then flows in the opposite direction, then ….  Like current from the wall outlet (60Hz)

Circuit Elements  Battery or other voltage source  causes  Wires  allow the current to.  Resistors,  allow current to flow,  but resist the flow, so  The more current flows or the bigger the resistance, the faster energy is lost: P = I 2 R +

Circuit Elements  Capacitor  does not allow charge to  charge flows into one side,  and out of the other,  so one side becomes __, the other __.  Energy is stored in separated charges.  Inductor  allows the current to flow in a loop,  so it acts like a  Energy is stored in magnetism

Impedance  Impedance is voltage/current,  Z = V/I  How much ______ flows in response to ______.  Resistors resist flow  independent of  don’t care  Z = R

Impedance of Capacitor  Capacitors  can resist flow because of their ____  flow of charge of the same sign is resisted  flow of charge of opposite sign is enhanced  impedance is less for AC, especially hi freq  Z = 1/2  f C

Impedance of Inductor  Inductors  resist flow because they have magnetism  that opposes change (change not charge!)  impedance is greater for AC, especially hi freq  Z = 2  f L

Summary  Electricity and Magnetism  exert forces on charges and magnets.  Electricity and magnetism affect each other:  current in coil acts like magnet  changing magnetic field induces current  Current flow occurs in circuits with voltage source  Impedance of current flow comes from  resistors, capacitors, inductors  Exam Friday