 # Chapter 5 Electrostatics

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Chapter 5 Electrostatics
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
Primary purpose of an x-ray tube is to convert electric (A/C current) into ELECTROMAGNETIC ENERGY!

Laws of electrostatics
Unlike charges ATTRACT Like charges REPEL Electrostatic force is DIRECTLY proportional to the PRODUCT of the charges and the SQUARE or 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

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

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

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)

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.

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

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

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

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

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!

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

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

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

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”

Types of Transformers Closed core Autotransformer Shell type