Electromagnetic Energy, Electricity, & Magnetism – Chapters 4 & 5

Vocabulary flashcards covering key terms from Chapters 4 and 5 on electromagnetic energy, electricity, and magnetism.

Photon

The smallest discrete quantity of electromagnetic energy; travels at light speed and contains oscillating electric and magnetic fields.

Speed of Light

Constant velocity of electromagnetic photons in vacuum: 3.0 × 10⁸ m/s.

Amplitude

Half the total height between a sine wave’s crest and valley; indicates wave strength.

Crest

The highest point of a sine wave.

Valley

The lowest point of a sine wave.

Cycle

One complete positive and negative oscillation of a sine wave.

Frequency

The number of wave cycles that pass a point per second; measured in hertz (Hz).

Wavelength

The distance from crest to crest or valley to valley in a wave.

Ionizing Radiation

EM radiation with enough energy to remove electrons from atoms; x-ray energies extend from 0 keV to the selected kVp.

Kilovolt Peak (kVp)

The maximum voltage applied to an x-ray tube; sets the upper limit of photon energy produced.

Attenuation

Reduction in EM radiation intensity due to scattering and absorption within matter.

Inverse Square Law

Radiation intensity is inversely proportional to the square of the distance from the source (I ∝ 1/d²).

Doubling Distance Rule

Doubling distance from a source reduces radiation intensity to 25 % of its original value.

Halving Distance Rule

Halving distance from a source increases radiation intensity by a factor of four (400 %).

Electrostatics

The study of stationary electric charges (+ or −).

Electrostatic Law of Attraction

Unlike charges attract; like charges repel.

Electric Potential (Volt)

Work per unit charge available to move electrons; measured in volts (V).

Conductor

Material through which electrons flow easily, e.g., copper, gold, aluminum, water.

Insulator

Material that resists electron flow, e.g., rubber, glass, plastic, porcelain.

Semiconductor

Material that can act as either conductor or insulator under different conditions.

Ohm’s Law

Relationship V = I × R, linking voltage, current, and resistance.

Electric Current

Flow of electrons through a conductor; measured in amperes (A).

Direct Current (DC)

Electric current with electrons moving in one direction only.

Alternating Current (AC)

Electric current with electrons reversing direction; standard U.S. power is 60 Hz.

Magnetism

Phenomenon produced by moving electric charges; any charged particle in motion creates a magnetic field.

Magnetic Permeability

Ability of a material to become magnetized.

Magnetic Retentivity

Ability of a material to retain magnetism after the external field is removed.

Electromagnetic Induction

Production of electric current in a conductor placed in a changing magnetic field.

Fleming’s Hand Rule

States that the induced magnetic field is oriented at 90° to electron flow.

Induction Motor

Device using sequentially energized electromagnets to rotate the x-ray tube’s anode.

Transformer

Device that changes AC voltage and current magnitudes via electromagnetic induction.

Autotransformer

Single-coil transformer with taps that provide variable voltage.

Step-Up Transformer

Transformer with more secondary than primary turns; increases voltage, decreases current.

Step-Down Transformer

Transformer with fewer secondary than primary turns; decreases voltage, increases current.

Transformer Law

Voltage ratio equals turns ratio: Vs/Vp = Ns/Np; current ratio is inverse to turns ratio.

AC Requirement for Transformers

Transformers operate only with alternating current, which supplies the changing magnetic field needed for induction.

Safety Role of Transformer

Adjusting voltage and current reduces electrocution risk and protects imaging equipment.