104 Ch. 6

CREATING THE X-RAY BEAM

Overview of X-Ray Beam Creation

  • Primary Function of X-Ray

    • Electric Energy: The energy moves in the x-ray tube, generating a significant amount of heat (99%).

    • Electromagnetic Energy: This constitutes the x-rays, which form about 1% of the total energy produced.

Basics of Electrostatics

  • Definition: Study of stationary charges, which can either be positive or negative.

  • Common Type: Most commonly involves negative charges because electrons are free to move.

Electrification Processes

  • Mechanisms of Electrification:

    • Contact: Electrification occurs when a charged object touches another object.

    • Friction: Involves the removal of electrons from one object when it is rubbed against another.

    • Induction: Refers to charge transfer without direct contact; charges rearrange due to the presence of another charged object nearby without touching.

Fundamental Laws of Electrostatics

  • 1st Law: Repulsion and Attraction

    • Principle: Unlike charges attract each other, while like charges repel each other.

  • 2nd Law: Coulomb’s Law

    • Concept: The electrostatic force between two charges is directly proportional to the product of the charges and inversely proportional to the square of the distance separating them.

    • Mathematical Formula:
      F=KracQ<em>1Q</em>2d2F = K rac{Q<em>1 Q</em>2}{d^2}

    • Variables:

    • FF = electrostatic force/potential energy (V)

    • KK = constant (often taken as 1 or other values)

    • QQ = magnitudes of the charges

    • dd = distance between the charges

    • Implication: If the distance between charges doubles, the force decreases by a factor of 4 (inverse square law).

    • Potential Energy:

    • Like charges possess potential energy when close (due to repulsion).

    • Unlike charges possess potential energy when apart.

  • 3rd Law: Law of Distribution

    • Charge Behavior: External positive charges will attract negative charges.

    • Uniform Distribution: The distribution of electric charges on the surface is uniform, while the inside of a conductor remains neutral.

    • Behavior of Charges: Charges attempt to repel one another.

  • 4th Law: Concentration Law

    • Surface Concentration: Electric charge tends to concentrate at the surface of a conductor, especially at points of highest curvature.

    • Ionization: When electrons concentrate too closely, they can ionize surrounding air, discharging at points of lower concentration to neutralize excess charge.

  • 5th Law: Law of Movement

    • Movement of Charges: Movement of electric charge occurs along solid conductors, primarily involving the movement of negative electrons.

Types of Electrical Materials

  • Guidelines for Conductivity: Different materials possess varying capacities to conduct electricity.

Electrodynamics

  • Definition: The study of moving electric charges.

  • Current Flow: Electric charges (specifically, electrons) move when there exists a potential difference.

Current Flow vs. Electron Flow

  • Direction of Flow:

    • Current Direction: Flows from positive to negative (+ to -).

    • Electron Flow: Moves from negative to positive (- to +).

Circuits

Overview of Electric Circuits

  • Definition: A closed path that allows for continuous charge flow, influenced by resistance and current.

  • Components of Circuits:

    • Current (I): Measured in amperes (A), representing the rate of charge flow per second.

    • One ampere is equivalent to one coulomb per second (1 A = 1 C/s).

    • Potential (V): Measured in volts (V), indicating the electrical pressure or potential difference.

    • Resistance (R): Measured in ohms (Ω), representing the opposition to current flow.

Units of Power and Measurements

  • Power (P): Refers to the rate at which energy is consumed or used.

    • Unit: Watt (W), where 1 W = Joule/second.

    • Formula:
      P=IVP = IV
      where II is current in amperes, and VV is potential in volts.

  • Resistance and Impact:

    • Ohm’s Law:
      V=IRV = IR

    • Relationship: As resistance increases, current decreases.

Types of Current

  • Direct Current (DC):

    • Electrons flow in a single direction, beginning at zero and reaching maximum potential at peak.

  • Alternating Current (AC):

    • Electrons oscillate, flowing in one direction in the first half of the cycle and then reversing in the second half.

    • Waveform is represented by a sine wave, commonly observed in U.S. current at 60 Hz.

Basic Components of Electric Circuits

  • Essential Components:

    • Conductor: Material, usually wire, that allows current to flow.

    • Power Source: Battery or similar device providing the necessary voltage.

    • Switch: Device to turn the circuit on or off.

    • Resistor: A component that reduces current flow, providing resistance to the electrical pathway.

  • Potential Difference: The difference in electric charge will create attractive forces between charges.

Factors Affecting Resistance

  • Influences on Resistance:

    • The length of the conductor affects resistance; longer wires increase resistance similar to a longer road causing more traffic.