2 22.1 Current & Circuits Electricity did not become an integral Part of our daily lives untilScientists learned to control theMovement of electric charge.This is known as current
3 Electric currents are responsible For many things; computers, Cars, and every move you make.Current is the rate at whichElectric charges move throughA given area.
4 Conventional current is defined In terms of positive movement. Electricity is the movement ofElectrons, the negative charge,Moving in a direction. This directionIs in the positive direction.
5 Solutions that have dissolved Ions can be charge carriers, These are called electrolytes.Drift velocity is the net velocityof a charge carrier moving inAn electric field.
6 Drift speeds are relatively small. The speed of an electron in aCopper wire is only aboutm/s! The electricField, on the other hand, isAlmost the speed of light.
7 Batteries and generators Supply energy to charge carriers. Both batteries and generatorsContain a potential difference(volts) across their terminals.Batteries use chemical energyAnd generators use mechanicalEnergy.
8 Current can be direct or alternating. In Direct Current (DC) the chargeMoves only one way through theWire. (like my electric truck)In Alternating Current (AC), theCharges are constantly changing,Creating no real movement ofElectrons.Our house current in the US is60 Hz.
9 Q = charge through a given area I = electric currentQ = charge through a given areat = time
10 The SI unit for current is the Ampere (A). The SI unit for charge is theCoulomb (C).So the Ampere is 1 C per second.
11 The amount of charge that passes Through the filament of a PROBLEM...The amount of charge that passesThrough the filament of aCertain light bulb in 2 s is1.67 C. Determine the current inThe light bulb.I = A
12 There are insulators and Conductors, but there are also Not so good conductors.The impedance of the motion ofCharge through a conductorIs the conductor’s resistance.Resistance is the ratio of thePotential difference acrossA conductor to the currentIt carries.
13 SI unit for resistance is the Ohm, VIR =SI unit for resistance is the Ohm,And is represented by Ω.
14 Ohm’s law states that the Resistance is constant over a Wide range of appliedPotential differences.It is usually shown by…V = IR
15 Ohm’s Law: V = I x RUsed to determine V, I, & R at all parts of a circuit.It means:A 1V circuit with a 1Ω Resistance will produce a current of 1A.Adding more resistors to a circuit will decrease the current produced.Increasing the voltage will increase the current produced.
16 Resistance depends on length, Cross-sectional area, material, And temperature.Resistors can be used to controlThe amount of currentIn a conductor.
17 The plate on an iron states that The current in the iron is 6.4 A PROBLEM...The plate on an iron states thatThe current in the iron is 6.4 AWhen the iron is connected acrossA potential difference of 120V.What is the resistance of the iron?R = 19 Ω
18 Electric power is the rate of Conversion of electrical energy. P = IVThe SI unit is the Watt.
19 Power = the rate of doing work (Work/time) Electrical Power = Current x VoltageP = I x VUnits: Watts
20 An electric space heater is Connected to a 120 V outlet. The PROBLEM...An electric space heater isConnected to a 120 V outlet. TheHeater dissipates 3.5 kW of powerIn the form of heat. CalculateThe resistance of the heater.R = 4.1 Ω
21 An electric circuit is a Continuous path through which Electric charges can flow.There are two types of circuitConnections…Parallel & Series
22 A parallel circuit is one with Several current paths, whose Total current equals the sum of theCurrents in its branches.
23 A series circuit is one in which Current passes through one Device and then another.
25 22.2 Using Electrical Energy Electric companies measure Energy consumption inKilowatt-hours.1 kW h = 3.6 X 106 J
26 Electrical energy is transferred at High potential differences to Minimize loss. (up to V)When the wires are strung, they areVery tight and straight, they bowBecause they are soooo hot!
27 How much does it cost to operate A 100 W light bulb for 24 hours PROBLEM...How much does it cost to operateA 100 W light bulb for 24 hoursIf electrical energy costs $0.08Per kW h? What is the cost perYear? What is the cost if you usedA energy conserving bulb at 14 W?Cost = $0.19/day $69/yearCost = $ 0.03/day $9.81/year
28 Current moving through a resistor Causes it to heat up because Flowing electrons bump into theAtoms in the resistor.These collisions increase theAtoms’ kinetic energy and, thus,The temperature of the resistor.
29 P = I2R V2 R P = V2 R E = t If we rearrange Ohm’s Law, and The formula for power, we have3 new formulas that we can use…And for the thermalEnergy dissipated…P = I2RV2RP =V2RE =t
30 Power Electrical Energy is usually converted to Electromagnetic Energy (light),Thermal Energy (heat),or Kinetic Energy (motion).
31 A heater has a resistance of 10 Ω. It operates on 120 V. PROBLEM...A heater has a resistance of10 Ω. It operates on 120 V.What is the power dissipated byThe heater? What is the thermalEnergy supplied by the heaterIn 10 s?1.44 kW kJ
33 Remember that there are 2 23-1 Simple CircuitsRemember that there are 2Types of circuits…Series&Parallel
34 * Electrons flow in a conductor. * Must have a closed circuit (loop). 2. Current Electricity* Electrons flow in a conductor.* Must have a closed circuit (loop).Charge = number of transferred electronsMeasured in Coulombs (C)
35 Current = electron flow (I) (like water flow) Measured in Amperes (A)Voltage = electrical potential energy (V)(like water pressure) Measured in Volts (V)
36 Resistance = ease that current can flow (like pipe diameter)Measured in Ohms (Ω)Resistor= item in circuit that causes resistance.Resistors “use up” a circuit’s voltage.Ex: Light Bulb
37 Circuit = the path that flowing electrons follow If path is continuous, it’s a closed circuitand electricity can flow.If path is interrupted, it’s an open circuitand electricity can NOT flow.
38 Series Circuits Current goes through one pathway only. Same amount of current goes through each component (battery, resistor, etc.).The total resistance of resistors in series = the sum of each resistance(add them up).
40 In a series circuit, all of the Resistors are added together In order to get theEquivalent Resistance.R = R1 + R2 + R3 + …See that the equivalent resistanceIs greater than any individualResistor, therefore if the voltageDoes not change, adding moreResistors always decreases current
41 Three 20 Ω resistors are connected In series across a 120 V generator. PROBLEM...Three 20 Ω resistors are connectedIn series across a 120 V generator.What is the equivalent resistanceOf the circuit? What is the currentIn the circuit?R = 60 ΩI = 2.0 A
42 Parallel Circuits Current divides into 2 or more paths Voltage drop across components is equal.The sum of the current in each parallel path = the total current in (or out) of the circuit.
44 In a parallel circuit the resistance Is always smaller than any One resistor because there areMore branches for the currentTo flow through.Equivalent Resistance for Parallel1/R = 1/R1 + 1/R2 + 1/R3 + …
45 Three 15 Ω resistors are connected In parallel and placed across PROBLEM...Three 15 Ω resistors are connectedIn parallel and placed acrossA 30 V battery. What is theEquivalent resistance? What is theCurrent through the entire circuit?What is the current through eachBranch of the circuit?R = 5 ΩI = 6 AI = 2 A
46 Draw a circuit diagram of a series circuit and a PROBLEM...Draw a circuit diagram of aseries circuit and aParallel circuit that each containThe following…Battery, motor, 3 lights, and 2Resistors.
47 There are many safety devices When dealing with electrical Circuits. 23-2 ApplicationsThere are many safety devicesWhen dealing with electricalCircuits.A short circuit is when theResistance is very small whichMakes the current very large.
48 When a short happens enough Thermal energy is produced to Start a fire, or just melt theWires if you’re lucky.A fuse is used to help stop a shortBefore it gets too bad.When a fuse is connected to thecircuit it will melt and “blow”Before the wires do.
49 A circuit breaker is another kind Of fuse. It breaks the circuit when theCurrent gets too high and aSwitch flips. In order to fixThe circuit, all you have to do isFlip the switch back.
50 A ground fault interrupter (GFCI) is a kind of electrical outlet that Breaks the circuit at the plugInstead of the circuit/fuse box.
51 An ammeter is a device used to Measure the current in a circuit. It is added in series andHas a low resistance.A voltmeter measures theVoltage of a circuit.It is added in parallel and hasA high resistance (10 kΩ).A multimeter measures bothAnd more.