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.

• 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

• 120v = N p 1 60000v Ns 500

34 Transformer Review N • Turns Ratio S • Step Up N P – V I

• Step Down – V I • Transformer Law N V I S S P NP VP IS

17 Transformer Law NS VS IP 35 NP VP IS

• 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

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.

22 Series Circuit Formula: 45

T • Current: I = I1 =I2 =I3 T • Voltage: V = V1 + V2 + V3 • Resistance:

• RT = R1 + R2 + R3

Parallel Circuit Rules 46 Current: IT = I1 + I2 + I3 Voltage: VT = V1 = V2 = V3 Resistance: • 1 1 1 1

• RT = R1 + R2 + R3 • (REMEMBER TO FLIP SIDES RT/1)

23 47 Review Problems on Handout Set up the formulas

• 4. What is the total current in a series circuit with 3 resistances, each supplied with 10 amperes?

• 5. What is the total voltage in a series circuit with 3 resistances, each supplied with 10 volts?

• 6. What is the total resistance of a series circuit with resistances of 2.5, 4.2, 6.8?

48 Review Problems on Handout Set up the formulas • 4. 10 amperes

• 5. 30 volts

• 6. 2.5, 4.2, 6.8= 13.5

24 49 Review Problems on Handout Set up the formulas

• 7. What is the total current in a parallel circuit with 3 resistances, each supplied with 10 amperes?

• 8. What is the total voltage in a parallel circuit with 3 resistances, each supplied with 10 volts?

• 9. What is the total resistance of a parallel circuit with resistances of 2.5, 4.2, 6.8?

50 Review Problems on Handout Set up the formulas • 7. 30 amperes

• 8. 10 volts

• 9. 1/2.5, 1/4.2, 1/ 6.8 • = 0 .4 + .24 + 0.14 = .79/1 = 1.26

25 Find the Resistance: 51

• What is the total resistance • of a parallel circuit • with resistances of 10, 10 , 20 ?

• What about a series circuit?

52 What type of circuit is this?

26 CIRCUITS 53 • Short Circuit

• Resistance = Reduces The Flow Of Electricity • (Too Much Will Blow Out Circuits) • HIGHER RESISTANCE=LOWER FLOW Of Electrons

54 FUSE – ENCASED IN GLASS

• IN THE CASE OF A SHORT CIRCUIT – • THE HIGHER CURRENT WILL MELT THE FUSE – STOPPING THE FLOW OF ELECTRICITY • CIRCUIT BREAKERS HAVE REPLACED FUSES - POWER TOO HIGH IT WILL CUT OFF – not damage appliance

27 55

• A circuit breaker acts in the same manner as a fuse. If the current flowing through it rises above a certain level, the circuit breaker flips its internal switch to open the circuit and stop the electric flow. • Any short circuit that lets the current rise to a dangerously high level will "trip" the circuit breaker and shut the system down. After the problem is corrected, the circuit breaker can be switched back on.

56 ELECTRIC GROUND

• 2 WIRES CONDUCT CURRENT • 3RD WIRE CONNECTED TO A GROUND SOURCE

• KEEPS CURRENT FROM A LOOSE WIRE GOING DIRECTLY TO PERSON • CURRENT ESCAPES THROUGH YOU

28 Ground 57 • A type of protection comes from a way of wiring circuits with an electric ground . Grounding is a process of connecting the electrical device to • Ground to prevent the earth via a shock conductor. - if there is a lose wire – without a ground the electrons try to escape through your body

58 X-ray imaging system

• Convert electric energy to electromagnet energy.

• A well controlled electrical current is applied and converted to mostly heat and a few x-rays.

29 ELECTROMAGNETISM 59 Electrodynamics study of electric charges in motion How the current • Conductor = electrons flow easily gets to the TUBE • Insulator = electrons Insulated cables do not flow • Semiconductors = some conditions behaves as an insulator and others a conductor.

• Magnetic force similar to electric force = 60 • Electric fields = exists around any charged particle • Electromagnetism = fields • When charged particles move = a magnetic field is induced • Every moving charges produces a magnetic field

30 FERROMAGNETIC 61

OBJECTS THAT CAN BE MAGNETIZED (IRON, COBALT, NICKEL) • SIMILAR TO BALLOON • 3 TYPES OF MAGNETS • LODESTONE – NATURAL (PERMANENT) • ARTIFICAL – N & S INDUCED • ELECTROMAGNET – temporary • Ferromagnetic material magnets produced by moving electric such as iron attracts current magnetic lines of induction, whereas nonmagnetic material such as copper does not.

MAGNETS 62

• USUALLY MADE OF IRON • EVERY MAGNET HAS A NORTH AND SOUTH POLES • LIKE SIMILAR CHARGES REPEL • OPPOSITES ATTRACT

31 63 TESLA –measurement of magnetic strength - used in MRI

• Demonstration of magnetic 64 lines of force with iron filings

• NORTH & SOUTH POLES

• If a single magnet is broken into smaller and smaller pieces, baby magnets result

32 65

• A moving charge creates a magnetic field

• When a charged particle is in motion – a magnetic force field perpendicular to the motion is created

Solenoid & Electromagnet 66 • A coil of wire is a helix • Supplied with current it is a solenoid • SOLENOID: Current flowing through a wire coil of wire • Add an iron core – simple form of ELECTROMAGNET • Putting a magnet in the middle of the coil of wire increases the strength if the electromagnet’s magnetic field

33 67 ELECTROMAGNETISM

• A MOVING CHARGE CREATES A MAGNETIC FIELD • In Electromagnetism - MOVEMENT OF ELECTRONS IN A ELECTRIC CURRENT THAT CREATS AN ELECTRIC FIELD

• SEEN ON A COMPASS

RT HAND RULE 68

• Current flow direction of thumb – • Magnetic filed – fingers • An electric current is considered to be a + flow • The negatively charged electrons are moving in the direction opposite to the current flow

34 69 RT HAND RULE

• Direction of magnetic current lines

• When wire is looped – magnetic field is strengthened = 2x more • Adding more loops – increases strength • Magnetic lines curve around to other pole

TRANSFORMER PRINCIPLE 70

• When the wire that is INCREASE # OF conducing the current is looped COILS OF WIRE • The magnetic field is INCREASES THE strengthened VOLTAGE • It is now 2x as strong • The MORE the LOOPS – • The STRONGER the field

35 71 Armature

• A coil of wire that is rotated in a magnetic field • More turns of coil the higher the voltage

• Look at diagram of x-ray tube – • Armature surrounds neck of anode

How Electric & Magnetic 72 Fields Interact

Faraday discovered that the magnetic lines of force and the wire must have a motion relative to each other to induce an electrical current

36 ELECTROMAGNET INDUCTION 73

• Moving a wire through a magnetic field will induce a current (Faraday) • Wire or field can move • Moving a magnet through a coil of wire will induce an electrical current

“Faraday’s Laws : or how to 74 increase the strength of the induced current • Increase the Strength of field or size of magnet • Increase the SPEED of motion • Change the ANGLE (more perpendicular) • Increase the Number of Turns of coil

37 75 ELECTROMAGNETIC INDUCTION 3 WAYS TO CREATE MOTION BETWEEN LINES OF FORCE AND A CONDUCTOR • Move the conductor through mag field • Move magnetic lines of force • Vary the magnetic flux

76 ELECTROMAGNET INDUCTION

• MOVING A BAR MAGNET THROUGH A COIL OF WIRE WILL INDUCE A CURRENT TO FLOW THROUGH THAT WIRE

38 INCREASING VOLTAGE 77

• Increasing the number of coils of wire will increase magnetic field strength – • Increasing the number of coils moving in a magnetic field will increase the voltage induced • Doubling the # of turns of wire = Doubles the Voltage

78 INCREASING CURRENT

• Increasing the strength (size of bar) of the magnetic field will increase the current • Increasing speed of motion through wires will increase current

39 79 Increasing Current

• 2 turns of coil and moved 1 / sec

• 4 turns of wire (2x more) and moved 3/sec

• How much stronger is current? • 2 x 3 = 6 times stronger

80 Angle of motion

• Motion of the wire perpendicular to the magnet (magnetic field) produces more current than a magnet that is at an oblique angle

40 81 Faraday’s law ?

Regulate the strength of the induced current BY INCREASING: • ______of the Magnet • ______of the motion • ______of the magnet • ______on the conduction coil

82 Faraday’s law

Regulate the strength of the induced current • Strength of the Magnet • Speed of the motion • Angle of the magnet • Number of turns on the conduction coil

41 AC – magnetic field 83 moves in and out MUTUAL INDUCTION

84 MUTUAL INDUCTION (STEP UP & DOWN TRANSFORMERS)

42 85 Transformer Design pg 95

Closed core (open) auto Shell type

SELF INDUCTION 86 • SIMILAR TO 2 COILS WRAPPED ON ONE CORE • (Self induction occurs in single coil of wire – the flow of electrons in one direction produces a current (in the same wire) – then when flow of current changes – polarity of magnet changes)

43 87 AUTOTRANSFORMER

88 Autotransformer – Self Induction

• There is only one wire – but works like when there are 2 wires = • The windings are used as the primary and secondary coils • The induced voltage varies on where the outside wires are connected (KVP Taps)

44 89 TRANSFORMERS

• STEP UP OR DOWN • OPEN CORE, CLOSED CORE OR SHELL TYPE • ABOUT 95% EFFICIENT • AUTOTRASFORMER = _____ induction • Functions to provide ______• Both types require AC for operation

90 A transformer with more secondary windings than primary windings ____. 1. has a greater secondary voltage 2. has a greater power output than input 3. is a step-down transformer 4. none of the above

45 Transformer Efficiency 91 • All transformers must operate on AC to provide the collapsing magnetic fields that induce the voltage changes in the secondary coil • Ideal Effciency – no loss Reality best = ~95% induction • Loss due to – Cu (copper) resistance – (Copper loss) resistance to flow in a conductor • (lg) wire diameter will reduce loss – Eddy currents • Laminating the core reduces eddy loss – Hysteresis – occurs in the core due to the loss of energy because of constant changing AC current) • Improved using silicon core material

92

• A C ELECTRONS SWITCH DIRECTIONS OF FLOW • RECTIFIED = DC

• A LOOP OF WIRE ROTATED IN A MAGNETIC FIELD = PRODUCES A CURRENT – WIRE FLIPS BACK & FORTH

46 93 Electric Motor

• Current supplied creates and electric field around the coils are moved by the magnetic field. The motion makes the motor turn

• Direct Current makes sure the motor only turns in one direction

• An electric generator produces an electrical current 94 • by rotation loops of wire through a fixed magnetic field

47 Examples of Electric Circuit Elements

95

Generators- convert mechanical energy to electrical energy 96 • High Voltage – • Falling Load • Increases the output • Type of generator used in voltage from capacitor discharge autotransformer to the kvp • Voltage falls approx 1 kvp/mas • operates at shortest time + highest mA • uses series of steps (mA + t) to achieve mAs • Where are these used?

48 High Voltage 97 generator • THAT CREATE AN ALTERNATING CURRENT ARE CALLED: • AN ALTERNATOR – • CONVERT MECHANICAL ENERGY INTO ELECTRICITY

98 generators

• Function to change ______energy in to ______energy

• Electrical current flowing through a conductor in one direction is ______

• A battery is a source of direct current

49 Circuit Sections Control Console High Voltage X-Ray Tube – Line monitor Circuit – Autotransformer – Step-up transformer – Line compensator – Rectification circuit – kVp selection – mA meter – mA Selection – X-ray tube – Timing circuit – Time selection Filament Circuit – Step-down transformer – Focal spot selection – Filaments 99

100

50 101

Circuit Diagram of Imaging System

102

51