Electromagnetic Radiation Notes

Electromagnetic Radiation

Topic Learning Outcomes

• Describe electromagnetic radiation.
• Differentiate ionizing and non-ionizing radiation.
• Illustrate the wave of electromagnetic radiation.
• List the properties and characteristics of electromagnetic radiation.
• List the sequence of electromagnetic spectrum in various conditions.
• Describe the duality principle of electromagnetic radiation.
• Describe the energy propagation of the electromagnetic radiation.
• Identify the appropriate equation or formula according to the given mathematical problems.
• State the value of velocity of light and Planck’s constant.
• Solve mathematical problems.

Introduction

• Radiation is energy traveling through space in wave form.
• Includes visible light, UV light, radio waves and particles.
• Two types: ionizing and non-ionizing.
• Ionizing radiation breaks molecular bonds, causing chemical reactions.
• Non-ionizing radiation can shake or move molecules.

Electromagnetic Radiation

• Photon: contains only energy, no mass or weight.
• Examples: radio signals, light, X-rays, gamma rays.

Ionizing vs. Non-Ionizing Radiation

Ionizing Radiation

• Carries enough energy to ionize an atom or molecule.
• Examples: far UV light, x-rays, gamma rays, fast-moving particles.
• Poses higher health risks and is destructive to living tissues.

Non-Ionizing Radiation

• Does not carry enough energy to ionize living material.
• Examples: visible light, near UV, infrared, microwave, radio wave.
• Poses fewer health risks, but long-term exposure may pose a risk.

Electromagnetic Spectrum

• Ranges from cosmic rays and gamma rays (high frequency) to radio waves (low frequency).
• Ionizing radiation (potentially harmful or beneficial): cosmic, gamma, X-rays, ultraviolet.

Properties of EM Radiation

• Sinusoidal waves composed of electric and magnetic fields.
• Magnetic field is at a right angle to the electric field.
• Travels through a vacuum at the speed of light ($3 \times 10^8$ m/s).
• Interaction occurs by absorption or scattering.

Characteristics of EM Radiation

• Obeys duality principles.
• No mass (for non-particle).
• Unaffected by electric and magnetic fields.
• May be polarized and show interference and diffraction.
• Attenuation/absorption obeys the exponential law.
• Transmission obeys the inverse square law.
• Travels in straight lines but trajectory can be altered by interaction with matter.

Wave Quantum Duality

• Wave Model: Higher frequency is shorter wavelength; lower frequency is longer wavelength.
• Particle Model: Waves consist of discrete packets of energy called photons.
• $E = h f$ (Energy equals Planck's constant times frequency).

Wave Characteristics

• Frequency: rate of oscillation (Hertz).
• Wavelength: distance between adjacent crests or troughs.
• $c = f \lambda$ (speed = frequency x wavelength).

Particle Characteristics

• Photons are emitted and absorbed by charged particles, acting as transporters of energy.
• Photon absorption excites electrons to higher energy levels; release emits a photon.

Wave and Particle Behavior

• Waves can pass through each other and superpose, showing interference effects.
• Particles cannot pass through each other; they bounce or shatter.

EM Radiation Characteristics

• Velocity: All EM radiation travels at the same velocity ($c$) in a vacuum (approximately $3 \times 10^8$ m/s).
• Frequency: Rate of vibration or oscillation. $f = 1/T$.
• Period: Time required to complete one cycle of the wave.
• Wavelength: Distance between two identical points on adjacent cycles.
• Amplitude: Maximum height of peaks or valleys.
• Energy: $E = hf = h c/\lambda$, where $h$ is Planck's constant.
• Intensity: Decreases as distance increases, obeying the Inverse Square Law.

Energy Propagation

• EM radiation propagates as perpendicular electric and magnetic fields.
• Components oscillate at right angles to each other and to the direction of propagation.
• Travels in straight lines and can be reflected, refracted, or absorbed.