Light Properties and Interactions

Light Properties

• A light wave, like an electromagnetic wave, has a wavelength and a frequency.
• Wavelengths of light waves are very short, measured in nanometers (nm).
• Wavelengths range from about 400 nm to 700 nm.
• Different wavelengths of light are seen as different colors.

Electromagnetic Spectrum

• Includes gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, and radio waves.

• Mechanical waves:

  • Their energy is related to amplitude.
  • Example: A water wave with a high amplitude has a lot of energy.

• Electromagnetic waves (like light):

  • Their energy is related to frequency, not amplitude.
  • As the frequency increases, the wavelength decreases.
  • As the frequency of an electromagnetic wave increases, the energy of the wave increases.

What is Light?

• Light is electromagnetic radiation you can see.
• Electromagnetic radiation is a type of wave created by vibrating particles.
• Light carries radiant energy.
• Light does NOT need a medium to travel.
• Electromagnetic waves are classified by:
  • Wavelength (the distance between two crests)
  • Frequency (how many waves pass a point in a second)

Types of Electromagnetic Waves

• Radio waves
  • Low frequency and energy
  • Wavelength between 30 cm to a kilometer or more
  • Uses: Communication
• Microwaves
  • Low frequency and energy
  • Wavelength between 1 mm and 30 cm
  • Uses: Cooking
• Infrared
  • Shorter than a microwave but longer than visible light
  • Uses: TV remote control
• Visible light
  • The range of wavelengths between infrared and ultraviolet
  • Uses: Perception of all colors
• Ultraviolet
  • Shorter wavelength, higher frequency, and energy than visible light
  • Uses: Can cause chemical reactions
• X-rays
  • High frequency and energy, short wavelength
  • Uses: Medical imaging
• Gamma rays
  • Highest frequency and energy, shortest wavelength
  • Uses: Can kill living cells

Brightness

• Brightness is a person's perception of the light's intensity.
• Definition of Intensity: The amount of energy passing through a square meter of space in one second.

Factors Affecting Brightness:

• Energy emitted by the light source:
  • Example: Light from a flashlight is much less intense than light from the Sun.
• Distance from the light source:
  • Closer = more intense.
  • Farther = less intense.

How Light Interacts with Matter

• Different types of matter interact with light in different ways.
• The three ways light interacts with matter:
  • Transmission
  • Absorption
  • Reflection

1. Transmission

• Definition: Transmission happens when light passes through a material.

• Types of Transmission:

  • Transparent Material:
    • Allows almost all the light to pass through.
    • Objects are seen clearly.
    • Example: Clear glass window, clean water, plastic wrap.
    • In transparent materials almost no distortion of the image.
  • Translucent Material:
    • Allows most of the light to pass through, but scatters the light.
    • Objects appear blurry.
    • Example: Frosted glass, wax paper, milk jugs.
    • In translucent materials the light scatters blurry vision.

• Transmission lets light continue traveling after passing through the material.

2. Absorption

• Definition:
  • Absorption happens when a material takes in most of the light that strikes it.
  • No light passes through the material.
• Characteristics:
  • Absorbed light energy often turns into heat.
  • You cannot see objects through materials that absorb light.
  • The material appears dark or opaque.
• Examples:
  • Opaque Materials:
    • Block the light completely.
    • Examples: Thick curtains, wooden doors, black cloth.

3. Reflection

• Definition:
  • Reflection happens when light bounces off the surface of a material.
• Important Points:
  • If the surface is smooth, the reflected rays stay organized, and you can see a clear image.
  • If the surface is rough, the reflected rays scatter, and the image is blurry or distorted.
  • This bouncing of light waves is called reflection.
• Examples:
  • Smooth Surface Reflection:
    • Mirrors
    • Calm water
  • Rough Surface Reflection:
    • Wall
    • Bumpy surfaces

Summary Table