Basic Electricity

Basic Electricity • All material is made of atoms (we think) • Atoms are comprised of • Nucleus: protons (+) and neutrons • Fixed • Electrons (-) orbit outside the nucleus

Basic Electricity • Electrons and protons are charged • Opposite charges attract • Like charges repel • In other words, charges desire to be “zeroed” or “neutralized” or “balanced”

Basic Electricity • How tightly electrons are bound depends on material • Tightly bound electrons: insulator • Does not conduct electricity (or heat) well • glass, plastic, rubber • Loosely bound (“free”) electrons: conductor • Conducts electricity (and heat) well • metals • In between: semiconductors • Important for computer chip production • silicon, germanium, carbon

Basic Electricity The copper atom has one lonely electron in the valence shell, just hanging out, waiting to be stripped away. It’s a good conductor.

battery +++++ +++++ +++++ +++++ • - - - - • - - - - • - - - - • - - - - - - - - - - - - - - - Voltage • Charge imbalance • caused by chemical • reactions  • Charges desire to • be neutralized  • Charges flow! • What causes electrons to flow? • Protons fixed; Electrons “free” • Electrons move!

battery +++++ +++++ +++++ +++++ • - - - - • - - - - • - - - - • - - - - - - - - - - - - - - - Voltage • There must be a complete path between excess + and excess – charges • Otherwise + and – charges don’t “see” each other

Voltage • A battery has regions of excess negative and positive charges caused by chemical reactions • The amount of “push” exerted on the electrons is called “electromotive force” • unit: volt (V) • Voltage is relative, only is meaningful when talking about voltage difference between 2 points

battery +++++ +++++ +++++ +++++ • - - - - • - - - - • - - - - • - - - - - - - - - - - - - - - Voltage • Do batteries run out of charge? • What happens to total # of electrons? Nothing! Electrons do not get used up – energy does!!

- - - - - - - - - - Count ‘um passing here! Current • Number of electrons that pass a certain point in a certain time: current wire • Unit: Ampere (amp) = 6.25  1018 electrons/s • Or Amp = 1 Coulomb/second

- - - + + + - + Current • Historically, current discussed in terms of positive charge flow: “conventional” current flow – actually it’s wrong! • Electrons (-) actually flow to the (+) • Symbol for battery:  Equivalent 

Time Delay? • Does it take time for electrons to flow from a switch to a bulb? Light Bulb 10 miles - - - - - - - - - - - - -

Time Delay? • Does it take time for electrons to flow from a switch to a bulb? • NO!! Wire is already full of electrons! Light Bulb Light Bulb 10 miles - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Current • How much current will flow? • Wire is broken? Zero (need a complete circuit) • Large voltage – large current • Small voltage – small current • All other things being equal! • For a given V, current depends on how much of the electron’s energy is used up: • Wire: electron’s energy  overcomes friction • Light bulb: electron’s energy  light and heat • Motor: electron’s energy  turns motor

Resistance • Measure of energy “used up” • Depends on the material (and temperature) • Resistance: opposition to electron movement • Unit: Ohm (); • Wires: very low resistance (often neglected) • Insulators: very high resistance (often assumed to be infinite) • As resistance increases, it takes more “push” (voltage) to cause a current Ohm’s Law I = V / R

Resistance • SPEED of electron’s is NOT effected by voltage! Currents transfer energy essentially instantaneously! • Why? Wires are already full of “free” electrons!! • First electron into wire causes one to pop out • Symbol of resistor: • Often called “loads”

AC/DC • Batteries produce “direct current” (DC) • Current is steady • One direction • “Wall outlets” provide “alternating current” (AC) • Current oscillates back and forth • More on this later…(old movie)

Power Law • Power is the rate at which energy is being delivered or consumed Power = (Current)(Voltage) P = IV • Units: Watt (W) • So if 2 A of current is flowing through a load at 120 V, the Power used by the load is P = IV = (2A)(120V) = 240 W

Power Law • How much current flows through a household (120 V) 60 W light bulb? P = IV I = P/V = 60 W / 120 V = 0.5 A

Power vs. Energy • What’s the difference? • Power (Watts): Rate at which energy is used or delivered. Doesn’t accumulate, and cannot be stored in a bucket • Energy (kWhrs): A quantity that accumulates, or can be stored in a bucket Energy = Power x Time

How to measure voltage and current • Think “voltage across” and “current through” • When measuring voltage, + and - probes are inserted in the circuit where you want to measure the voltage difference. V

How to measure voltage and current • When measuring current, the circuit must be broken so the current flows through the meter A

In Summary • Electricity is the flow of electrons through a conductor driven by an electromotive force • V = IR (Ohms Law) • P = IV (Power Law) • Energy = Power x Time

Flux Magic Rectified to DC (one phase shown) An electrically charged particle moving in a magnetic field will experience a force (known as the Lorentz force) pushing it in a direction perpendicular to the magnetic field and the direction of motion: Source: http://www.wondermagnet.com/magfaq.html#q18 Most of the electric power in the world is 3 phase. The concept was originally conceived by Nikola Tesla and was proven that 3 phase was far superior to single phase power. 3 phase power is typically 150% more efficient than single phase in the same power range. In a single phase unit the power falls to zero three times during each cycle, in 3 phase it never drops to zero. The power delivered to the load is the same at any instant. Also, in 3 phase the conductors need only be 75% the size of conductors for single phase for the same power output. source: www.windstuffnow.com/ main/3_phase_basics.htm

Basic Electricity