**Electricity, Magnetism, and Electromagnetism** Bushong Ch. 5 RTEC 244

**Objectives** • Review of Planck’s Equation (B, Ch. 4) • Electrostatics • Electricity • Ohm’s Law • Series & Parallel Circuits

**Particle Model: Quantum Theory** • X-ray is identified among all EM energy by their energy. • Measured in electron volts (eV) • X-ray = 10 keV to 50 MeV • Wavelength 10 -10 to 10 -14 m • Frequency 10 18 to 1022 Hz

**E = hf – Planck’s Equation** • E = phonton enerty • h = Planck’s constant • f = frequency • How are energy of a photon and frequency related?

**Electrification ** • Electrons are often free to travel from one valence shell to another. • An object is electrified it is has too few or too many electrons.

**Atom construction** • Because of electron binding energy, valence e- often are free to travel from the outermost shell of one atom to another. • What do we know about e- binding energy of an atom?

**ELECTRIFICAITON OF OBJECTS** • FRICTION • CONTACT • INDUCTION ELECTRIFICATION BY CONTACT ELECTRONS LEAVE YOUR BODY – CONTACT THE BALLOON

**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

**THAT CREATE AN ALTERNATING CURRENT ARE CALLED:** AN ALTERNATOR – CONVERT MECHANICAL ENERGY INTO ELECTRICITY EX: PORTABLE GAS, ENGINE - GENERATOR Generator - convert mechanical energy to electrical energy

**The Earth** • A huge reservoir of stray electric charges – electric ground

**Smallest unit of electric charge** • Electron • Electric charge is the coulomb

**Laws of Electrostatics** • Unlike charges attract; like charges repel • Coulomb’s law: The force is directly proportional to the product of the charges and inversely proportional to the square of the distance.

**Electrostatic Laws** • Electric charge distribution is uniform throughout or on the surface. • Electric charges of a conductor is concentrated along the sharpest curvature of the surface. • Pg. 74

**Electric Potential** • Energy = ? • Electric charges have potential energy, when positioned close to each other.

**ELECTRIC POTENTIAL (EMF)** • MEASURED IN VOLTS • Potential difference between two charges that makes the current flow ( there does not have to be an actual flow – just the potential difference – • The force or strength of electron flow • 220 volts sent to x-ray machines • Joule is the SI unit for both mechanical energy and work

**VOLT= THE POTIENTAL 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

**How the current gets to the TUBEInsulated cables**

**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.

**Electrodynamics study of electric charges in motion** • Conductor = electrons flow easily • Insulator = electrons do not flow • Semiconductors = some conditions behaves as an insulator and others a conductor.

**Electric Circuits** • Modifying electric flow and controlling electricity results in an electric circuit.

**CURRENT** • RATE OF ELECTRON FLOW • AMPERE OR AMP • 1 AMP = 1 COULOMB FLOWING IN 1 SEC • AC = 60 CYCLES PER SEC (50 IN EUROPE)

**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

**AC E FLOW ALTERNATELY** DC E FLOW IN ONE DIRECTION P 82

**Capacitors** • A device that is capable of accumulating and storing an electrical charge A parallel plate capacitor

** High Voltage Generator- transformers & rectifiers** • High Voltage – • Increases the output voltage from autotransformer to the kvp • Falling Load • Type of generator used in capacitor discharge • 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?

**generators** • Function to change _______energy in to ___________energy • What components are included in the high voltage generation or generator • Electrical current flowing through a conductor in one direction is _______ • A battery is a source of direct current

**WHAT MEASURES ELECTRIC POTIENTAL = VOLT** • CURRENT = AMP • ELECTRIC CIRCUIT IS THE PATHWAY FOR ELECTRIC CURRENT

**Resistance (OHM)** • The amount of opposition to flow Conductor – material that permits electrons to flow easily Insulator - inhibits the flow of electrons

**OHMS LAW V = IR** • V = POTIENTAL • A = AMPS (CURRENT) • R = RESISTANCE (OHMS)

**OHM’S LAW:** • V = Potential difference in volts • I = Current in amperes • R = Resistance in ohms () • V= IR I =V/R R=V/I

**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

**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

**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

**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

**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

**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

**Electric current** • Electricity = the flow of electrons along a conductor. • E- travel along a conductor in two ways. • Alternating current (AC) - sine wave • Direct current (DC) • X-ray imaging systems require 20 to 150 kW of electric power. • Circuit symbols and functions. Pg. 80

**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)

**Simple SERIES Circuit**

**EX:CHRISTMASLIGHTS** One line – all bulbs go out Separate lines Only bulb burns out PARALLEL & SERIES circuit

**Series Circuit Rules:** • Current: IT = I1 =I2 =I3 • Voltage: VT = V1 + V2 + V3 • Resistance: • RT = R1 + R2 + R3

**Parallel Circuit Rules** • Current: IT = I1 + I2 + I3 • Voltage: VT = V1 = V2 = V3 Resistance: • 1111 • RT = R1 + R2 + R3 • (REMEMBER TO FLIP SIDES RT/1

**Set up the formulas** • What is the total current in a series circuit with 3 resistances, each supplied with 10 amperes? • What is the total voltage in a series circuit with 3 resistances, each supplied with 10 volts? • What is the total resistance of a series circuit with resistances of 2.5, 4.2, 6.8?

**Answers** • 4. 10 amperes • 5. 30 volts • 6. 2.5, 4.2, 6.8= 13.5

**Set up the formulas** • What is the total current in a parallel circuit with 3 resistances, each supplied with 10 amperes? • What is the total voltage in a parallel circuit with 3 resistances, each supplied with 10 volts? • What is the total resistance of a parallel circuit with resistances of 2.5, 4.2, 6.8?

**Answers** • 7. 30 amperes • 8. 10 volts • 9. 1/2.5, 1/4.2, 1/ 6.8 • = 0 .4 + .24 + 0.14 = 1/.78 = 1.28