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Chapter 4 Electricity, Magnetism , Electromagnetism

Chapter 4 Electricity, Magnetism , Electromagnetism. Photon Energy Photon energy is DIRECTLY proportional to its frequency Photon energy INCREASES as wavelength DECREASES Photon energy INCREASES as kVp INCREASES. Electricity, Magnetism and the x-ray tube relationship.

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Chapter 4 Electricity, Magnetism , Electromagnetism

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  1. Chapter 4 Electricity, Magnetism, Electromagnetism • Photon Energy • Photon energy is DIRECTLY proportional to its frequency • Photon energy INCREASES as wavelength DECREASES • Photon energy INCREASES as kVp INCREASES

  2. Electricity, Magnetism and the x-ray tube relationship • Primary purpose of an x-ray tube is to convert electric (A/C current) into ELECTROMAGNETIC ENERGY!

  3. Laws of electrostatics • Unlike charges ATTRACT • Like charges REPEL • Electrostatic force is DIRECTLY proportional to the PRODUCT of the charges and the SQUARE of the distance between them (kind of like Inv. Sq. law and laws of magnetics) • When objects are “electrified, the charges are distributed throughout the object – BUT are greatest at POINTED spots

  4. Electric Terms • Electrodynamics – electron flow • Conductors – Matter that conducts the current • Insulators – Matter that INHIBITS current flow • SUPERCONDUCTOR – Like an MRI unit – low resistance (niobium/titanium) • Semi-conductor = depending on the conditions, can be either a conductor/insulator

  5. Electronic Terms, con’t • Electric Potential = Volt (V) • Resistance = Increasing electric resistance (Ohm’s) = LESS current flow in amps (A) • Ohm’s Law = voltage across the circuit is equal to the CURRENT X RESISTANCE (V + IR) where I= current (amps), R= resistance in ohm’s, V= POTENTIAL in volts • WATT (W) = measurement of electrical power

  6. Current • Direct Current (DC) = electron flow in only one direction • Alternating current (AC) SINUSOIDAL form each way (+ & -) • Magnetism and AC are very closely related (+/- OR N-S pole charges) • Magnets are classified according to their origin (natural, permanent, electromagnet)

  7. Magnetic Laws • Every magnet has TWO poles • Like poles REPEL, unlike ATTRACT • Magnetic lines are ALWAYS closed • Magnetic force and the DISTANCE from the magnet are INVERSLEY proportional to the square of the distance – BUT the attraction is GREATEST at the POLES rather than the sides of the magnet.

  8. 4 Fundamental forces of nature • Gravity • Strong nuclear forces • Weak nuclear forces/interaction • Electromagnetic force(s)

  9. The Battery • Discovered (invented) by “Volta” who made a “voltaic “ pile (copper, zinc and wet paper) = 1st crude battery and SOURCE of EMF!

  10. Charges in motion • Can create a magnetic field (flux lines, gauss, tesla) • The book takes a lot of time with the “right hand rule” spend your time on other items: • Solenoid – coil of wire that MAGNIFIES the action of the current flow via COILS • Electromagnet – ferromagnetic material wrapped in a coil of wire

  11. FARADAY • Found that a coil of wire & a mangetic field that is MOVING can cause current (AMPS) to flow in the wire coil – INDUCTION OF CURRENT – Farady’s law • Magnitude of induced current depends on: • Strength of magnetic field • Velocity of the magnetic field as it moves past the conductor (coil) • ANGLE of the conductor (coil) to the magnetic field • NUMBER of TURNS in the conductor

  12. LENTZ’ Law • Induced current flows in a direction such that it opposes the action that induces it • Two ways to induce current: • Self induction – single coil of wire with a current running through it – OPPOSES the magnetic forces it produces • Mutual induction – inducing a current flow through a secondary coil by passing a varying current through the primary coil – VERY IMPORTANT FOR TRANSFORMERS!

  13. Electric Generator • Simple electric generator: coil of wire placed in a strong magnetic field between tow poles of a magnet

  14. Electric Motor • Electric energy applied to the “current loop” to produce a mechanical motion – rotation of the loop in the magnetic field – like the stator windings on the x-ray tube – able to have the anode turn w/o any current on the inside of the tube – INDUCTION motor

  15. TRANSFORMERS • Change the intensity of the AC voltage and current by MUTUAL INDUCTION • Voltage and AMPS may be changed (stepped up or down) by changing the numbers of coils on each side of a transformer

  16. Transformer Energy Losses • Resistance to current = heat loss • AC reversal currents = hysteresis (self induction current flow opposes magnetic field) • Magnetic current fluctuation from + to - = “Eddy currents”

  17. Types of Transformers • Closed core • Autotransformer • Shell type

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