Presentation on theme: "Physics for Electricity"— Presentation transcript:
1 Physics for Electricity CHAPTERPhysics for Electricity3Instructor Name: (Your Name)
2 Learning Objectives Use Watt’s law to solve for electric power Discuss the concepts of electrical fields and magnetic lines of forceExplain how an electron magnet is formedPut in your own words how a voltage is induced in a conductor by movement through a magnetic field
3 Learning Objectives (continued) Describe how an inductor and capacitor store energyDiscuss how a negative voltage spike is generated when current flow through an inductor is ceasedExplain the similarities between a capacitor and an accumulator used in a hydraulic system
4 Electric PowerWork is force that results in movement in the direction the force is appliedThe amount of force exerted times distance traveled (lb-ft) yields the amount of work performedPower is the rate at which work is performed, in other words the amount of work over a period of timeElectrical power is measured in watts
5 Watt’s LawElectrical power is calculated by multiplying current by voltageWatts=Amps x Volts (P=IE or PIE)Volts=Watts ÷ AmpsAmps=Watts ÷ VoltsP=Watts (Power)I=CurrentE=Voltage
6 Magnetism Current flow produces magnetism Magnetism can produce current flowEvery magnet has two distinct poles, north pole and south poleMagnetic lines of force (magnetic flux) are present between the north and south poles of all magnets
7 Magnetic Lines of Force Figure 3-1 Magnetic lines of force illustrated by iron filings.
8 Arrows Indicate Direction the North End of a Compass Will Point Figure 3-2 Directional arrows on magnetic lines of force indicate direction the North end of a compass needle would point when placed in the magnetic field.
9 Magnetism (continued) Opposite poles of a magnet attract each otherThe attraction of unlike poles increases as they get closer to each otherLike poles of a magnet repel each otherThe repulsion of the like poles increases as they get closer to each other
10 Reaction of Unlike and Like Poles of a Magnet Figure 3-3 Unlike magnetic poles attract; like magnetic poles repel.
11 Current Flow and Magnetism Figure 3-4 Lines of force around a current-carryingconductorFigure 3-5 Right hand rule of thumb
12 The Strength of the Magnetic Field Surrounding a Conductor is Directly Proportional to the Current FlowFigure 3-8 Magnetic field around conductor with 1 amp of current flow and 3 amps of current flow.
13 Magnetic Fields Cancel Out Space Between Conductors Causing the Conductors to Move Closer Figure 3-10 Magnetic field cancels out in the space between conductors with current flow in same direction. This causes two conductors to move toward each other.
14 Two Conductors With 10A of Current Combine to Produce 20A of Current Figure 3-11 Two conductors with 10A of current flowing through each conductor has the same combined magnetic field strength as 20A flowing through a single conductor.
15 When Current Flows Through a Loop of Wire the Magnetic Fields Combine to Form a Single Stronger Magnetic FieldFigure 3-12 Magnetic field around one loop of a conductor.
16 ElectromagnetReluctance is the opposition to the “flow” of magnetic lines of forceSome materials such as nickel, iron and steel, provide a path of less reluctance for magnetsWhen current flows through a wire wrapped around an iron core the magnetic lines of force will concentrate on the core and create a strong magnet, an electromagnet
17 ElectromagnetFigure 3-14 Adding an iron core to the coil to form an electromagnet.
18 Creating Current Flow With a Magnet If a conductor is passed through a magnetic field so the field “cuts” through the conductor a voltage is induced in the conductorOnly movement that is 90° to the magnetic lines causes a voltage to be induced into the conductorIt does not matter if the magnet or the conductor is moved, a voltage will be induced
19 Cutting Lines of Force Induces a Voltage in a Conductor Figure 3-16 Cutting magnetic lines of force to induce a voltage in the conductor: conductor is moving from the right to the left perpendicular to the magnetic lines of force.
20 Movement Parallel to Lines of Force Result in No Induced Voltage in the Conductor Figure 3-17 Up and down movement of conductor parallel to magnetic lines of force resulting in no induced voltage because no magnetic lines of force are being cut by the conductor.
21 Inductors An inductor is a wire that is wound in a series of coils Inductors have a core of ferrous metalInductors are rated in henriesInductors store energy in the form of a magnetic fieldAn inductor will inhibit the initial flow of current, known as counter electromotive force (CEMF)Once current flow is interrupted an inductor will try to maintain the flow
22 Current Flow Through an Inductor Figure 3-22 Magnetic field surrounding an inductor with no change in current flow.Figure 3-23 Decreasing current flow through inductor
23 Lenz’s LawLenz’s Law: The polarity of an induced voltage is such to oppose the change in current that produced it.Figure 3-24 Current flow through an inductor is interrupted causing a reverse-polarity voltage to be induced across the inductor as the magnetic field surrounding the inductor collapses.
24 Inductor Suppressed by Parallel Resistor Figure 3-26 Inductor suppressed by parallel resistor limits the negative voltage spike to a low amplitude.
25 Transformer Used to Step Up a Changing Voltage Figure 3-27 Transformer steps up a changing voltage: a transformer cannot increase a DC voltage.
26 Spark Ignition System Used on Gasoline Engines Figure 3-28 Spark-ignition system utilizes a negative voltage spike and a type of transformer to produce thousand of volts.
27 CapacitorsCapacitors are electrical devices used to store energy in the form of an electric fieldCapacitors consist of two metal plates spaced close togetherA thin non conductive material, a dielectric material, separates the platesA dielectric has a very high resistance valueThe metal plates of the capacitor are connected to the electrical circuitCapacitors are rated in farads
28 Capacitors Store Energy in the Form of An Electric Field Figure 3-33 Capacitor stores energy in the form of an electric field.
29 Capacitor in a Circuit Figure 3-34 Capacitor charging. Figure 3-35 Capacitor maintaining its charge.Figure 3-36 Capacitor discharging.
30 WorkWork is an activity that involves force and movement in the direction of that force, as described by the equation:Work = Force x DistanceWork is measured in pounds-feetIf a 500 pound weight is lifted one foot that equals 500 lb-ft of work
31 Energy Energy is the capacity or ability to perform work Energy is measured in pounds-feetKinetic energy is the energy of motionHeat is a form of energyPotential energy is energy that is stored and ready to perform some amount of work
32 Horsepower =(Torque x RPM) ÷ 5252 Power is the rate at which work is donePower is often measured in watts or horsepowerOne horsepower is defined as the amount of power necessary to lift 550 lbs at a rate of one foot per secondOne horsepower is equal to 746 wattsThe equation to calculate horse power is:Horsepower =(Torque x RPM) ÷ 5252
33 Kinetic Energy Kinetic energy is the energy of motion The amount of kinetic energy depends on the velocity and mass of the objectThe formula to determine kinetic energy is:KE= ½ x Mass x Velocity²
34 Forms of Potential Energy Gravitational Potential Energy (GPE)GPE = Mass x Acceleration Due to Gravity x HeightSpring potential energyChemical potential energy; an example of chemical potential energy is diesel fuel or gasoline
35 SummaryPower describes the rate at which work is being performed and has units of watts.Electric power measured in watts is the product of volts and amps.Magnetic lines of force are means of graphically illustrating the strength and orientation of a magnetic field. Magnetic lines of force are drawn so that they appear to originate at the north pole of a magnet and end at the south pole of a magnet.
36 Summary (continued)Like magnet poles repel each other and unlike magnetic poles attract each other. This attraction or repulsion increases at a rapid rate as the distance between two magnets decreases.Current flow through a conductor causes a magnetic field to encircle the conductor. The direction of the arrows on the magnetic lines of force can be determined using the right hand rule.
37 Summary (continued)A conductor that is carrying current is compelled to move out of a strong magnetic field into a weaker magnetic field.A wire that is formed into a coil is called an inductor. Inductors store energy in the form of a magnetic field. Inductors are rated in units of henries.
38 Summary (continued)Current flow through an inductor causes a magnetic field to surround a coil much in the same way that a magnetic field surrounds a permanent magnet. Placing a piece of metal such as iron inside the inductor causes the metal to temporarily become a magnet. The temporary magnet is an electromagnet. Electromagnets are used in many truck electronic components.
39 Summary (continued)Passing a conductor through a magnetic field so that lines of force are interrupted or cut by the conductor causes a voltage to be induced in the conductor. This is the basis of generators.Changing the current flow (increasing or decreasing) through an inductor causes the expanding or contracting magnetic field to induce a voltage across the coil. This is known as self-inductance.
40 Summary (continued)The polarity of voltage induced across an inductor due to a decreasing magnetic field is opposite the polarity of the voltage that produced the initial voltage flow through the inductor. This is described by Lenz’s law.The negative voltage spike produced by an inductor when current flow is rapidly interrupted can damage a truck’s electronic components. Suppression is typically used across the inductor to reduce the negative voltage spike.
41 Summary (continued)Capacitors store energy in the form of electric fields. Capacitors are rated in units known as farads.The time it takes for a capacitor to charge depends on the series resistance in the circuit. The larger the value of resistance, the longer it takes the capacitor to charge.