Electromagnetic Waves and Material Interactions

Electromagnetic Waves

• Electromagnetic waves are energy waves that are mostly invisible and can travel through empty space.
• Examples: light, microwave, x-ray, TV, and cell phone transmission.
• We are aware of a small portion of them: visible light (colors), infrared light (heat), and ultraviolet (sunburn).

Electromagnetic Spectrum

• Different types of electromagnetic waves, ordered by wavelength and frequency:
  • Radio waves: Wavelength ~ $10^3$ meters, Frequency ~ $10^4$ Hz, Size comparison: Buildings. Penetrates Earth Atmosphere?: Y
  • Microwaves: Wavelength ~ $10^{-2}$ meters, Frequency ~ $10^8$ Hz, Size comparison: Humans. Penetrates Earth Atmosphere?: Y
  • Infrared: Wavelength ~ $10^{-5}$ meters, Frequency ~ $10^{12}$ Hz, Size comparison: Honey Bee. Penetrates Earth Atmosphere?: N
  • Visible light: Wavelength ~ $0.5 \times 10^{-6}$ meters, Frequency ~ $10^{15}$ Hz, Size comparison: Pinpoint. Penetrates Earth Atmosphere?: Y
  • Ultraviolet: Wavelength ~ $10^{-8}$ meters, Frequency ~ $10^{16}$ Hz, Size comparison: Protozoans. Penetrates Earth Atmosphere?: N
  • X-rays: Wavelength ~ $10^{-10}$ meters, Frequency ~ $10^{18}$ Hz, Size comparison: Molecules. Penetrates Earth Atmosphere?: N
  • Gamma rays: Wavelength ~ $10^{-12}$ meters, Frequency ~ $10^{20}$ Hz, Size comparison: Atoms, Atomic Nuclei. Penetrates Earth Atmosphere?: N

Energy of Electromagnetic Waves

• Electromagnetic energy is created by vibrations that produce waves.
• Each wave emits a different level of energy.
• These waves travel at the speed of light.
• Each wave has a unique range of length, energy, and frequency.
• Frequency: The number of waves a vibration creates during a period of time.
• Higher frequency means greater energy of the radiation.

Visible Light

• Visible light is a group of electromagnetic waves.
• Each wavelength within the visible light spectrum represents a particular color.

Infrared Radiation

• Infrared radiation is a type of electromagnetic radiation that involves heat or thermal radiation.
• All objects emit and absorb thermal radiation.

Light Interaction with Objects

• Light can be absorbed, reflected, transmitted, or refracted.
  • Absorption: The loss of light as it passes through a material.
  • Refraction: The bending of light as it passes between mediums.
  • Transmission: The passage of light through a material.
  • Reflection: The return of light by a material.

Absorption Example: X-Rays and Lead

• X-rays can be harmful, so doctors minimize exposure.
• Protective clothing contains lead.
• Lead absorbs x-rays due to its high density, shielding the body from radiation.

Absorption Example: Microwaves

• Microwaves heat food by utilizing water molecules.
• Microwave energy is absorbed by water molecules, causing them to vibrate.
• These vibrations generate heat, warming the food.

Reflection

• Reflection occurs when light is returned by an object.
• Examples: mirrors and smooth water surfaces.
• Reflection involves an incident ray and a reflected ray.
• The angle of incidence equals the angle of reflection for smooth objects.

Reflection: Scattering of Light

• Rough surfaces cause light to scatter instead of reflecting at equal angles.
  • Specular reflection
  • Diffuse reflection

Transmission

• Transmission is the passing of light through an object.
• Objects have different levels of transmission:
  • Opaque objects: Reflect or absorb all light.
  • Translucent objects: Allow only part of the light through.
  • Transparent objects: Pass all light through.

Shadows

• Shadows are formed when light is blocked by an object.
• Opaque objects prevent light beams from passing through, creating shadows.

Refraction

• Refraction involves the bending of light as it passes from one substance to another.
• Example: Observing objects underwater.
• Refraction is due to a change in the speed of light.
• Light slows down and bends when passing from a less dense substance (air) to a more dense substance (water).
• Light speeds up and bends outward when passing from water to air.

Combined Interactions

• Light interaction can involve combinations of absorption, reflection, transmission, and refraction.
• Example: Blue jeans absorb all colors but reflect blue.

Temperature Change

• Electromagnetic waves can change the temperature of an object.
• Infrared radiation transfers heat to objects.

Material Properties

• Materials are chosen for specific applications based on their properties.
  • Thermal conductors: Conduct heat readily (e.g., metals).
  • Thermal insulators: Limit heat transfer (e.g., rubber, wood, styrofoam).
  • Electrical conductors: Allow flow of electrical current (e.g., metals).
  • Electrical insulators: Limit the flow of electrical currents (e.g., rubber, air, wood).

Conduction

• Conduction involves transferring heat between substances in direct contact.
• Example: Cooking pot on a stove. Heat is transferred from the stove to the pot (metal - thermal conductor) and the handle is made of rubber (thermal insulator)

Thermal Expansion and Contraction

• Materials can expand or contract due to the presence or absence of heat.
• Example: Thermometers use mercury (a good thermal conductor) that expands and contracts with temperature changes.

Electrical Properties of Materials

• Metals are good conductors of electrical current, allowing electrons to flow easily.
• Electrical insulators (nonmetals) do not let electrons flow easily.
• Insulators protect us from dangerous effects of electricity.

Summary of Key Terms

• Electromagnetic Waves: Group of energy waves that are mostly invisible and can travel through empty space.
• Frequency: Number of waves a vibration creates during a period of time.
• Visible Light: Range of electromagnetic spectrum that can be detected by the human eye.
• Infrared: Type of electromagnetic radiation that involves heat.
• Absorption: The loss of light as it passes through a material.
• Reflection: The return of light by a material.
• Transmission: The passage of light through a material.
• Refraction: The bending of light as they pass between mediums.
• Translucent: Allow only a part of the light through.
• Opaque: Reflect or absorb all light.
• Thermal Conductors: Materials that conduct heat readily.
• Thermal Insulators: Materials that limit heat transfer.
• Electrical Conductors: Materials that allow flow of electrical current.
• Electrical Insulators: Materials that limit the flow of electrical current.