Dc Circuits

Direct Current • We want electrons to flow in a wire – Why? • To Transfer Energy – from one form (electrical) to another ……………

Current • How will we get them to move? • If there is a region where there are more electrons, they will repel to a region where there are fewer electrons as long as there is a path(thru a conductor) • The flow will stop when the two regions have the same potential = same density of electrons.

Current • In order to have a continuous flow you must keep pumping electrons. • What is a Pump? • =voltaic cell, dry cell, wet cell, solar cell, photocell,…..

Circuits • Closed Circuit • -a closed loop through which electrons can flow • Pump • Load • Connectors(wires)

Circuits • A load is a device which reduces the potential • Ex – toaster, TV, Stereo, • The electrons do work, so it “loses” energy • W = qV from V = W/q

Voltage • Voltage is joules per coulomb or (W/q) • 1 joules is the energy required to move 1 coulomb of electrons across a potential of 1 volt • Or 1 electron-volt is the energy required to move 1 electron across a potential of 1 volt

Connectors • Small pieces of • As opposed to wire with no insulators which do load, v.v.v.low not contain free resistance and electrons. many free electrons - metals

Homer, retrieves the burnt toast! Was any work done?

Must it be plugged in to talk?

Ski Slope Analogy • • • •

Current is Power is Load is Pump is

Current • Rate of flow of e• Analogy = skiers/hour • Electrons per sec or • Coulombs per sec • I = q/t units are Amperes, amps • Measure with an ammeter

Power • Power is the rate at which you work or the rate at which energy is consummed • Work/time units are joules/sec or watts • P = W/t = Vq/t = VI • Sir James Watt – invented the steam engine

OHM”S LAW • Circuit Builder

I=V/R

OHM’s Law • What is the relationship between Voltage and Current? • Called Ohm’s Law • Only true for devices which do not heat up.

Fuses