Physics Electromagnetic Radiation

Overview of Electromagnetic Waves

  • Electromagnetic Spectrum: Range of electromagnetic radiation, marked by varying energy and frequency.

    • Spectrum definition varies; generally, it refers to a range of energies or frequencies.

    • Components include frequency, wavelength, and energy.

Electromagnetic Waves Basics

  • Electromagnetic Waves: Produced by accelerating charges, involving perpendicular electric and magnetic fields.

    • Moving electric field induces magnetic field and vice versa.

    • Properties:

      • Fields are perpendicular to each other and to the direction of propagation.

      • Carries energy in the form of electromagnetic radiation.

Spectrum Breakdown

  • Spectrum stretches from low frequency to high frequency:

    • Low Frequency: Longer wavelengths

    • High Frequency: Shorter wavelengths

Components of the Spectrum

  • Radio Waves: Example of low frequency; used for radio transmission (e.g., 96.5 MHz).

  • Microwaves: Higher frequency than radio, known for cooking applications.

  • Infrared: Associated with light and heat; found in sunlight.

  • Visible Light: Light visible to human eyes, wavelength range of 400-700 nm.

  • Ultraviolet: Beyond visible light, often from the sun; harmful without protection.

  • X-rays & Gamma Rays: High frequency; used in medical imaging and treatment.

Key Relationships

  • All electromagnetic waves travel at the speed of light ( 3 x 10^8 m/s) in a vacuum.

  • Wave Equation: Speed of light (c) = wavelength (λ) × frequency (f).

    • Higher frequency waves have shorter wavelengths and more energy.

Energy Properties

  • Energy of photons is directly proportional to frequency and inversely proportional to wavelength:

    • Gamma rays possess more energy than radio waves.

    • Clinical Implications: Different interactions with biological tissues based on frequency and energy.

Ionizing vs Non-Ionizing Radiation

  • Boundary: Occurs around 1 x 10^15 Hz, with implications for ionizing (above UV) and non-ionizing (below UV) radiation.

  • Ionization: Can break molecular bonds and cause damage in biological tissues.

Electron Volt (eV)

  • Definition: Energy gained by an electron when accelerated through 1 volt;

    • 1 eV ≈ 1.6 x 10^-19 Joules.

  • Important for understanding photon energy, especially in ionizing radiation scenarios.

Clinical Applications of Electromagnetic Waves

Shortwave Diathermy

  • Function: Gentle heating of deeper tissues (non-superficial), used to relieve pain, increase mobilization, and improve blood flow.

  • Frequency Range: Typically 10-100 MHz, commonly set at 27.12 MHz.

  • Considerations: Risk of superficial heating from strong conductors (e.g. metals) in patients.

Microwave Therapy

  • Similar to Shortwave: Provides deep tissue heating through the vibration of molecules.

  • Common Frequency: 2,450 MHz.

  • Precautions: Be vigilant of other forms of matter like bones that can reflect microwaves.

Infrared Radiation

  • Origin: Major component of solar energy;

    • Greater than half of the energy from the sun is infrared.

  • Applications: Used for muscle relaxation, blood vessel dilation, and thermography.

  • Risks: Can penetrate the eye and lead to retinal burns; importance of caution with infrared lasers.