Electricity and Magnetism

1. Electricity and Magnetism CVT 102

2. Principles of Electricity • Electron Theory • All electronic effects caused by movement of electrons • Serves as basis for design of electrical equipment

3. Atoms

4. Atoms • Composed of protons, electrons, neutrons • Nucleus • positively charged protons • neutral neutrons • Negative charged electrons travel in orbits around nucleus

5. Atoms • Atomic Number • Number of protons in the nucleus • Determines characteristics of atom • Mass Number • Number of protons and neutrons in the nucleus • On periodic table, given as average of commonly occurring isotopes

6. Atoms • Electrons • Revolve in shells or orbits • Close to nucleus — strong attraction; outer orbits — less attracted • Free electrons located in outer orbits; movement creates electric current

7. Principles of Electricity • Electron Theory • All electronic effects caused by movement of electrons • Serves as basis for design of electrical equipment • Atoms, Electrons, Matter • Matter has mass and occupies space; consists of atoms

8. Atoms, Electrons, Matter Atoms Composed of protons, electrons, neutrons Nucleus is center; contains positive charged protons and neutral charged neutrons Negative charged electrons travel in orbits around nucleus Atoms held together by opposite charges of protons and electrons Different elements have varying numbers of protons and electrons Principles of Electricity

9. Principles of Electricity • Atoms, Electrons, Matter • Electrons • Revolve in shells or orbits • Close to nucleus – strong attraction; outer orbits – less attracted • Free electrons located in outer orbits; movement creates electric current • Electricity: term actually describes movement of free electrons moving from orbit of one atom to another (principle based on Bohr’s Theory)

10. Principles of Electricity • Atoms, Electrons, Matter • Electronscon’t. • A conductor is a material that allows flow of free electrons • The greater the number of electrons in a substance, the better the conductor • Copper is the most commonly used material for a conductor. Silver, zinc and brass are also used. • Devices in O.R. that use copper as a conductor: surgical lamps, ESU, power drills • Water is a conductor; humidity in O.R. should be maintained at 50%-60%

11. Principles of Electricity • Insulators • Materials with small number of free electrons; inhibit flow of electrons • Basically poor conductors • Used to wrap conductors to preserve current and prevent leakage of electrons • Types of insulators • Rubber cord, plastic around ESU or X-ray machine

12. Principles of Electricity • Electrical Charge • Can be either positive or negative • Defined as too many or too few electrons orbiting an atom • Law of Electric Charge: like charges repel each other; unlike charges attract each other; opposites attract

13. Principles of Electricity • Electrical Current • Movement of electrical charge • Current moves through conductors by movement of free electrons migrating from atom to atom inside conductor

14. Magnetism • Magnetic Fields • Electrons create a magnetic field or electric charge while orbiting the nucleus • In some materials electrons travel in the same direction, combining magnetic fields • Natural magnetic substances include iron, nickel, cobalt, even the earth • Electrical generators depend on the close relationship of electricity and magnetism

15. Magnetism • Magnetic Fields con’t. • Earth • Two poles, north and south • Magnetic field is lines of magnetic force between poles • Magnetic field causes metal objects to be attracted to the magnet; needle in a compass

16. Magnetism • Electromagnets • Metals that become magnetic when encircled by a conductor • Magnetic field created by current traveling through conductor • Magnetic field used to create electricity • Electricity does not create power; only means for transporting it • Interaction between wires and magnets produces power

17. Magnetism • Electromagnets con’t. • Example: Power plant • Water from dam heated  forms steam  turns turbines (generators)  turbines spin magnets  electricity is created for use

18. Volts • Terminology • Volt is electrical potential – Voltage is potential energy of electrons –Named after Alessandro Volta, a 17th century scientist who invented the battery • Electric system: battery creates voltage to move electricity • Circuit is the path electricity travels

19. Current • Measured in amperes (amps) • Rate of flow of electrons • Current flow is the movement of free electrons • Free electrons attracted from point of excess electrons to a point with fewer electrons

20. Ohm’s Law • Scientific law of electricity –Mathematical equation showing how voltage, current, and resistance interrelate – Ohm’s Law: V = I x R • Resistance • Restricting flow of current; measured in ohms • Ohm’s Law –More voltage will increase current if resistance is constant; higher resistance causes decreased current if voltage is constant

21. Power • Rate at which work is completed • Rate of movement of electrons or current flow • Product of voltage & current is power • P = I x V • Measured in watts (W) • Converted to kilowatts (KW): 1 KW = 1,000 W • Example: DC Circuit is 12V & 20A, Power is P = 20 x 12 = 240W or 0.24KW

22. Load • Device that uses electricity to perform a function • Can change amount of energy from power source • Examples: surgical lamps, ESU, power drills, video monitors • Resistive energy loads: conductor has high resistance to flow of electricity • Example: filament (conductor) in light bulb; electricity has to force way thru resistance to cause filament to glow

23. Switch • Device used to open or close circuit • Controls flow of electricity • Example: Flashlight • Batteries (power) • Wires (conductors) connected to battery that is connected to switch activated by user • Bulb (load) must have voltage • Voltage carried by conductors and switch controls flow of current to load; open switch – no flow, closed switch bulb lights up

24. Wires • Hot Wire • Wire that connects to switch; colored red • Neutral Wire • Pathway for electrons to return to energy source; complete the circuit; colored green • Ground Wire • Sends leaking electrons to ground to prevent shock; colored black

25. Resistors • Devices made of materials that are purposely resistive • Designated with letter R

26. Direct Current (DC) • Electrical current flows in one direction – negative to positive pole • Example: Batteries • Serve as storage device; keep electricity until needed • Negative (-) and positive (+) terminals • When switch is closed, current flows from one terminal to the other

27. Direct Current (DC) • Batteries con’t. • Four components of DC circuit • Battery: source of electricity • Wire (battery to load): conductor • Switch: control device • Load: bulb

28. Alternating Current • Current that periodically reverses direction • Complete cycle is current that moves in one direction, then reverses direction • Hertz (Hz): one AC cycle • Frequency: number of AC cycles in a second; symbol ƒ • Most common AC in U.S. is 60 cycle AC • Typical voltage is 110V or 120V

29. Alternating Current • AC Can Change Voltage • AC delivered as high voltage, then “stepped down” • Example: • Transformers “step up” exiting voltage • Power lines (transformer) deliver electricity at high voltage • Voltage is stepped down before use

30. Radio Frequency (RF) • Frequency is number of wave cycles (one cycle is a hertz) per second • Radio and TV signals are electromagnetic waves • Radio transmitter delivers signal to antennae system • Electromagnetic signals travel through cable, air or optical fiber to receiving antennae • RF spectrum begins at 9 kHz (or less) to over 3 GHz

31. Isolated Circuit • Cause of electrical shock • Secondary circuit contains hazardous current due to isolated circuit • Transformer insulation isolates secondary circuit • Person touches both poles of non-insulated isolated circuit and experiences an electrical shock and/or burn

32. Isolated Circuit • Secondary Circuit con’t. • Two methods of prevention: • Solid insulation placed as total barrier to prevent complete access to circuit • Conductive barrier of insulation between isolated circuit and conductive barrier

33. Electrosurgery • Application of electrical current through tissue to coagulate bleeding or cut tissue • Electrosurgical Unit (ESU): Device that provides power for electric current • Electrosurgery: Electrical currents applied directly to tissue; utilizes AC current • Electrocautery: Uses heated wire to burn tissue; no electricity enters body; utilizes DC current

34. Electrosurgery • ESU Circuit: Current Flow • Generator  thru conductor cord  active electrode (Bovie tip)  surgical site (energy converted to thermal energy to cut or coagulate)  thru patient  dispersive electrode (grounding pad)  conductor cord  generator

35. Bipolar Electrosurgery • Used for delicate procedures, presence of moisture, prevent nerve damage • Two prongs of forceps: active and inactive electrodes • Current travels through one tip, passes thru tissue, disperses to other tip • No dispersive electrode required

36. Monopolar Electrosurgery • Flow of current is as described in Slide 35 • Dispersive Electrode (grounding pad) • Placement is critical to avoid electrical burns to patient • Pad must be in complete contact with patient’s skin • Pad pulled up or portion not in contact, may result in second or third degree burns to patient

37. Electrosurgery • Shock and Burn • Patient • Burns usually deep; tissue necrosis; thrombosis • Debridement • Sterile Surgery Team Members • RF Capacitive Coupling: AC travels from active electrode, through intact insulation, burns skin; apply active electrode beneath Crile held by surgeon to prevent burns

38. Electrosurgery • Shock & Burn con’t. • Sterile Surgery Team Members • Dielectric Breakdown: High voltage breaks down insulating material, such as sterile glove; produces hole in glove – surgical team member sustains small burn

39. Electrosurgery • Vaporized Tissue Plume • Occurs during procedures involving electrosurgery, lasers, power drills • Plume is vaporized tissue • Contains hazardous bioparticles that are carcinogenic, mutagenic, and they may carriy bloodborne pathogens • Surgical technologists utilize suction to “suck smoke” from wound when using electrosurgery or smoke evacuators for lasers

40. Principles of Electricity • Electricity • Describes movement of free electrons moving from orbit of one atom to another (principle based on Bohr’s Theory)

41. Principles of Electricity • Conductor • material that allows flow of free electrons • Copper is the most commonly used material for a conductor. Silver, zinc and brass are also used.

42. Principles of Electricity • Insulators • Materials with small number of free electrons; inhibit flow of electrons • Basically poor conductors • Used to wrap conductors to preserve current and prevent leakage of electrons • Types of insulators • Rubber cord, plastic, paper

44. Principles of Electricity • Electrical Charge • Can be either positive or negative • Charged is conserved • Neutral objects contain equal numbers of positive and negative charges • Like charges repel; unlike charges attract

45. Coulomb’s Law • The force (attraction or repulsion) between two charged particles is proportional to the product of their charges and inversely proportional to the square of the distance between them. (Inverse square law)

46. Electrical Charge • SI unit • Coulomb (C) • 6.25 X 1018 electrons • Very large amount of charge • Coulomb force between two charges of 1 .0 C each separated by 1 .0 m is 9X109 N (about 1 million tons)

47. Static Electricity • Charges on surface of object • Charge is greater on curved surface; greater the curvature, the greater the charge • Click here for more information about static electricity

48. Principles of Electricity • Electrical Current • Movement of electrical charge • Current moves through conductors by movement of free electrons migrating from atom to atom inside conductor

49. Magnetism • Magnetic Fields • Electrons create a magnetic field or electric charge while orbiting the nucleus • In some materials electrons travel in the same direction, combining magnetic fields • Natural magnetic substances include iron, nickel, cobalt, even the earth

50. Magnetism • Magnetic Fields • Earth • Two poles, north and south • Magnetic field is lines of magnetic force between poles • Magnetic field causes metal objects to be attracted to the magnet; needle in a compass