RTE214 Chapter 003

Electromagnetic Energy

• Chapter 3 of Bushong's textbook presents the principles surrounding electromagnetic energy and its applications in radiologic science.

Properties of Electromagnetic Energy

• Photons: Fundamental particles of light

• Energy Continuum: Electromagnetic energy exists continuously over a spectrum.

• Key Properties:

  • Amplitude: Height of the wave measured from the equilibrium position to the crest or trough.

  • Frequency (f): Number of wavelengths passing a point per second (measured in Hertz, Hz).

  • Wavelength (λ): Distance between two consecutive crests or troughs of a wave.

  • Velocity (v): Speed of light is approximately 3 x 10^8 m/s.

Wave Amplitude

• Describes the height of the sine wave, representing the energy or intensity of the wave.

• Amplitude is crucial for understanding signal strength in electromagnetic waves.

Frequency

• Defined as the rate at which wave cycles occur, expressed as how many cycles pass in one second.

• Measured in Hertz (Hz), with higher frequencies indicating more wave cycles occurring per second.

Wavelength

• Represents the spatial distance between repeating units of a wave; it is crucial in determining the energy carried by the wave:

  • Shorter wavelength corresponds to higher frequency, indicating higher energy.

The Wave Equation

• Wavelength and frequency are interrelated by:

  • Formula: λ = v / f

  • Alternatively: v = f λ

• Velocity remains constant at the speed of light for all electromagnetic waves.

Example Calculation

• To find the speed of sound with given frequency and wavelength:

  • Frequency (f) = 60 Hz, wavelength (λ) = 0.5 cm

  • Calculation: V = fλ = 60 Hz x 0.5 cm = 30 cm/s (or 0.3 m/s).

Electromagnetic Wave Equation

• Since all electromagnetic waves travel at the speed of light, their frequency and wavelength have an inverse relationship:

• Formula: C = f λ where C is the speed of light.

Frequency Calculation Example

• If the wavelength of green light is 8.2 x 10^-2 m:

  • Calculation: F = C / λ = (3 x 10^8 m/s) / (8.2 x 10^-2 m) = 3.7 x 10^9 Hz.

Electromagnetic Spectrum

• Covers the entire range of electromagnetic energy, comprising various wavelengths and frequencies.

• Constituents: Photons with varying electric and magnetic fields, traveling at light speed.

Ionizing Electromagnetic Radiation

• Types:

  • X-rays and Gamma rays: Both carry high energy but arise from different sources.

  • X-rays originate from electron shells, while gamma rays arise from the nucleus.

• Frequency of x-radiation is much higher and wavelength shorter compared to other electromagnetic energy types.

Wave-Particle Duality

• Discusses the dual nature of electromagnetic energy:

  • X-rays exhibit particle-like properties.

  • Visible light can display wave-like properties.

Attenuation of Electromagnetic Energy

• Attenuation: The reduction of intensity caused by absorption and scattering.

• Radiopaque vs. Radiolucent Structures:

  • Radiopaque: Structures like bones that absorb x-rays.

  • Radiolucent: Structures such as lungs or soft tissues that transmit x-rays.

Inverse Square Law

• Relates the intensity of radiation to the distance from the source:

  • I1 at distance d1 and I2 at distance d2.

  • Formula: I2 = (d1^2 x I1) / (d2^2).

Example of Inverse Square Law Calculations

• Given I1 = 4 mR at 3 ft, find I2 at 6 ft:

  • I2 = (3^2 x 4 mR) / (6^2) = 1 mR

Further Example Calculation

• Reading of 287 mRem at 1.5 cm:

  • Find distance for 28.7 mRem:

  • D2 = √(I1/I2) x d1 = √(287/28.7) x 1.5 cm = 4.74 cm.

Planck’s Quantum Theory

• Energy of a photon is denoted as:

  • E = hf where h is Planck’s constant and f is frequency.

Conservation Laws

• Conservation of Matter: Matter cannot be created or destroyed.

• Conservation of Energy: Energy cannot be created or destroyed; represented by:

  • E = mc^2 (where E is energy in Joules, m is mass in kg, c is speed of light in m/s).

Conclusion

• Notes conclude with acknowledgment of the content provided in Bushong's textbook and its significance in understanding radiological science.