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Electricity & Electromagnetism

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Electricity & Electromagnetism Circuitry, Formulas & Electricity 1 Ch5 Bushong RT 244 – 12 Lect # 3 RT 244 WEEK 10 rev 2012 2 LECTURE # 3 ELECTRICITY & ELECTROMAGNETISM TRANSFORMERS + ETC BUSHONG CH. 4 & 5 REF: CARLTONS CH 3, 4 & 5 & PHYSICS CD 4 & 5 1 • Wavelength is the distance 3 from the peak of one wave to the peak of the next wave. • Frequency refers to the number of waves that go by a specific point in one second. Remember that electromagnetic energy waves all travel at the same speed—the speed of light • Measured in • Hertz or angstrom 4 2 5 Electric Circuits • Modifying electric flow and controlling electricity results in an electric circuit. 6 Electric Potential • Energy = ?* • Electric charges have potential energy, when positioned close to each other. * EMF 3 Capacitors 7 • A device that is capable of accumulating and storing an electrical charge A parallel plate capacitor ELECTRIC POTENTIAL 8 (EMF) • Potential difference between two charges that makes the • Voltage is an expression current flow (there does not of electric potential. have to be an actual flow – just the potential difference – • electric potential is the • The force or strength of ability to do work due to electron flow separation of charges • The volt is equal to the • 220 volts sent to x-ray amount of work (joules) machines that can be done per unit of charge • Joule is the SI unit for both mechanical energy and work • Work of a battery 4 VOLT= THE POTIENTAL 9 DIFFERENCE • Voltmeter measures the voltage across the circuit • Ammeter – measures current • Ohmmeter- measures resistance of one resistor in circuit • switch must be closed for current to flow Properties Of Electricity 10 Voltage Current Resistance • the units of measure for electric potential (kev) = voltage • current = amperage • are the same units we use as technologists to express technical factors on the x-ray machine operating console. • kVp is kilovoltage peak and • mA is milliamperes. 5 CURRENT • People sometimes 11 mistakenly use the word • Rate of Electron Flow "volt" as if it referred to • Ampere or Amp the current passing • 1 Amp = 1 Coulomb through a conductor. Flowing In 1 Sec • the Volt refers to the • Ac = 60 Cycles Per Sec difference in electric (50 cycles in Europe) potential between the two charges that make the current flow. • The actual flow of electrons is current. 12 CURRENT (mA) • The # of electrons flowing past a given point per unit of time. • AC – Alternating current – when electrons flow in one direction and then the other • DC – when electrons all flow in one direction 6 Current flows in opposite direction 13 of the electrons • AC electrons • Flow Alternately • DC electrons • Flow in one direction Amperes = columbs/sec 14 • One ampere equals one coulomb flowing by in one second: • Voltage and amperes are related in terms of how they affect the strength of an electric current. 1. A low-voltage, high-amperage current has many electrons moving 2. A low-amperage, high-voltage current with fewer electrons moving may be just as powerful because of the higher potential. • Which one of the above describes the X-ray machine? 7 Resistance Ω ( OHM) 15 • Resistance is the property of an element in a circuit that resists or impedes the flow of electricity • The amount of opposition to flow • Conductor – material that permits electrons to flow easily • Insulator - inhibits the flow of electrons OHM’S LAW: V= IR 16 • States that the potential difference (voltage) across the total circuit or any part of that circuit is equal to the current (amperes) times the resistance. • V = Potential difference in volts • I = Current in amperes • R = Resistance in ohms () • V= IR • I =V/R • R=V/I 8 17 • ELECTRIC CIRCUIT IS THE PATHWAY FOR ELECTRIC CURRENT • What measures • Electric potiential ? • Current ? What are the definitions of each? State the meaning of Ohms Law 18 V = IR • The voltage across the total circuit or any portion of the circuit is equal to the current times the resistance. • According to Ohm’s Law, what would the voltage be if the resistance is 2 and the current is 4 ampere? • A. 2 volt • B. 4 volt • C. 8 volt • D. 10 volt 9 19 R = V/I • The resistance in a circuit is equal to the voltage divided by the current • According to Ohm’s Law, what would the resistance be if the voltage is 110 volt and the current is 5 ampere? A. 22 B. 55 C. 220 D. 550 20 I = V/R • The current across a circuit is equal to the voltage divided by the resistance. • According to Ohm’s Law, what would the current be if the voltage is 12 volt and the resistance is 1.5 ? • A. 2 Ampere • B. 4 Ampere • C. 6 Ampere • D. 8 Ampere 10 21 According to Ohm’s Law, • what would the resistance • be if the voltage is 220 volt and the • current is 10 ampere? 22 • 100 volts of potential difference causes a current of 2 ohms resistance • What amperage is produced? 11 Transformers & Formulas • Autotransformer • Step Up • Step Down TRANSFORMER FORMULAS 24 (STEP UP OR DOWN) • V = voltage • Vp = N p • N = # turns Vs Ns • p = primary • s = secondary • Vp = I s • I = current Vs Ip • Np = I s Ns Ip 12 Transformer Review 25 • Turns Ratio NS N P • Transformer Law NS VS IP NP VP IS • The number of turns in the primary and secondary coils of a transformer 26 determines whether it will increase or decrease voltage and by how much. In other words, the number of turns in the coil "cut" by this magnetic field determines the magnitude of the induced voltage as reflected by the transformer law formula: • Example: A transformer has 100 turns in the primary coil and 10,000 turns in the secondary coil (a turns ratio of 10,000/100 or 100/1). If 500V is applied to the primary side, what will the output voltage be? Calculate as follows: • Vs/500V = 10,000/100 Vs/500V = 100/1 Vs = 500V x 100 = 50,000V • Simply stated, if there are more turns in the secondary coil than in the primary coil, voltage will be increased. The opposite is also true: If there are more turns in the primary coil than in the secondary coil, voltage will be reduced. 13 27 Vp = N p Vs Ns • Transformer has a turns ratio of 1 to 200. There are 250 volts on the primary side, what is the voltage on the secondary side? 28 • The Transformer has 100 turns on the Primary side, 100 volts and 10 amps. The secondary side has 50,000 turns of wire. What is the current AND voltage supplied to the secondary side? • ____________ volts = ________ kVp __________ amps = ________mA 14 29 • A radiograph using 200 ma 1/20 sec 55 kvp of a hand was taken in a 3Ø 12p room. • What do you use in a single phase room? 30 PROBLEM: • A TRANSFORMER HAS A TURNS RATIO OF 1:500 • With a supply of 220 V and 50 Amps • What is the KVP + MA supplied to the tube? 15 31 • 200 = 1 x = 110,000 volts x 500 x = 110 kvp (volts to Kilovolts – remove 3 0’s - or move 3 spaces to the left) 1 = x x = .01 Amp or 100Ma 500 50 .01 = 100 (amps to milliamps – move 3 spaces to the rt) X-Ray Tube Circuit 32 What is the turns ratio? 16 33 • Vp = N p Vs Ns NS N P • 120v = N p 1 60000v Ns 500 N V I S S P N V I P P S 34 Transformer Review • Turns Ratio • Step Up – V I • Step Down – V I • Transformer Law 17 Transformer Law 35 • The Transformer has 100 turns on the Primary side, 100 volts and 10 amps. The secondary side has 50,000 turns of wire. What is the current AND voltage supplied to the secondary side? • ____________ volts = ________ kVp __________ amps = ________mAN V I S S P NP VP IS 36 What is responsible for supplying a precise voltage to the x-ray machine? THE TRANSFORMER 18 37 The Earth • A huge reservoir of • stray electric charges – electric ground 38 ELECTRIFICAITON OF OBJECTS ELECTRIFICATION BY CONTACT • FRICTION ELECTRONS LEAVE YOUR BODY – CONTACT THE • CONTACT BALLOON • INDUCTION 19 39 Electrification • Electrification = process of electrons being added or subtracted from an object • Balloon rubbed against your head (Friction)– Collects electrons from you - sticks to the wall that has a positive charge • Shuffling across wool rug – e on shoes • Touch door handle– e’s want to escape (Contact) • Induction – electrical fields acting upon each other – like in the circuitry of the x-ray equipment 40 X-ray Tubes have complicated wiring • SERIES CIRCUIT (all circuit elements are connected in a line along the same conductor • PARALLEL CIRCUIT (elements bridge the circuit rather than lie in a line along the conductor) 20 41 PARALLEL & SERIES circuit EX: CHRISTMAS LIGHTS One line – all bulbs go out Separate lines Only bulb burns out 42 Rules for Simple Series Circuits • The total resistance is equal to the sum of the individual resistances. • The current through each circuit element is the same and is equal to the total circuit current. • The sum of the voltages across each circuit element is equal to the total circuit voltage. 21 43 Rules for Parallel Circuit 44 • The sum of the currents through each circuit element is equal to the total circuit current. • The voltage across each circuit element is the same and is equal to the total circuit voltage. • The total resistance is the inverse of the sum of the reciprocals of each individual resistance.
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