CHAPTER 22

SECTION 1

  1. Light, just like sound, travels in waves. Sound travels as a longitudinal wave, light travels as a transverse wave.

Light: An Electromagnetic Wave

  1. Light is a type of energy. It is also known as electromagnetic energy.
  1. An electromagnetic wave is a wave that can travel through empty space or through matter.
  1. An electromagnetic wave has a magnetic field and an electric field that travel at right angles to one another.
  1. In an electromagnetic wave the electric and magnetic field are also at right angle, or perpendicular to the direction the wave is moving.
  1. The electromagnetic wave is produced by the vibration of a photon. A photon is an electrically charged particle.
  1. Every electrically charged particle has an electric field around it. When the particle vibrates, it causes the electric field to vibrate.
  1. If you have a moving electric field, you also create a magnetic field.
  1. The vibration of the electric and magnetic field produces the electromagnetic wave.
  1. The transfer of energy by electromagnetic waves is radiation.

The Speed of Light

  1. Nothing travels faster than the speed of light.
  1. In a medium-free environment, light travels at 300,000 km/sec (or 9.5 trillion km/year).
  1. In an environment with a medium, the light is slowed by the medium.
  1. The light waves from the sun are the major energy sources on Earth.

SECTION 2

  1. Electromagnetic waves can be arranged in order according to wavelength and energy level.

Characteristics of Electromagnetic Waves

  1. All electromagnetic waves travel at the same speed in a vacuum.
  1. The medium that any electromagnetic wave travels through will affect the wave’s speed.
  1. The electromagnetic waves can be arranged by wavelength and energy on the electromagnetic spectrum. The spectrum is divided into regions based on wavelength.
  1. The spectrum in order from longest wavelength, lowest energy to shortest wavelength, highest energy:

radio wave

microwave

infrared

visible light

ultraviolet

x ray

gamma ray

  1. Infrared waves are responsible for the warmth you feel on a sunny day. The energy of the wave causes the particles in your skin to vibrate more, increasing the temperature and causing you to feel warmer.
  1. Visible light is a band of colors: ROY G BIV
  1. The different colors of light have different wavelengths and energy levels.

SECTION 3

  1. Electromagnetic waves interact in various ways that affect the way we view our universe.

Reflection

  1. The law of reflection says that the angle at which light strikes a barrier will be equal to the angle at which it reflects off the barrier.
  1. If an object produces its own light, it is luminous. If it reflects the light of another object it is said to be illuminated.

Absorption and Scattering

  1. As light travels away from the object that produced it, the light gets dimmer and dimmer. This is due to absorption and scattering.
  1. When energy is transferred from a light wave to particles of matter that is absorption. This causes the light to become dimmer.
  1. Scattering is an interaction between light and matter that causes the light to change direction.
  1. After colliding with matter, light scatters in all directions. Light with a shorter wavelength is scattered more than that with a longer wavelength. This is why the sky appears blue.

Refraction

  1. Refraction is the bending of light as it passes from one medium to another.
  1. Refraction occurs because the speed of light varies according to the medium it is traveling through.
  1. The part of the wave that first enters the new medium starts traveling at a different speed before the rest of the wave does. This causes the bending to occur.
  1. Refraction results in optical illusions.
  1. Refraction also results in the formation of rainbows as the sunlight is refracted by the water drops in the atmosphere.
  1. Each color of light has a different wavelength. The colors with the shortest wavelength bend more than the ones with longer wavelength.

Diffraction

  1. Diffraction is the bending of waves around barriers or through openings.
  1. The amount a wave diffracts is determined by its wavelength and the size of the barrier/opening.
  1. Light waves cannot diffract very well around large objects.

Interference

  1. Interference occurs when 2 or more waves overlap.
  1. Interference may be destructive, which results in less amplitude than the original wave, or it may be constructive, which results in greater amplitude than the original wave.

SECTION 4

  1. Whenever light strikes matter it interacts with the matter.

Light and Matter

  1. Reflection happens whenever light bounces off of an object. It is reflected light which allows us to see objects that do not produce their own light.
  1. Absorption occurs whenever light energy is transferred to matter. Absorption causes the matter molecules to become more energized.
  1. Transmission is the passing of light waves through matter.
  1. Matter through which light is easily transmitted is said to be transparent. EXAMPLE: glass
  2. Translucent matter transmits light but scatters it as it passes through. EXAMPLE: wax paper
  3. Opaque matter does not transmit any light. EXAMPLE: metals

Colors of Objects

  1. The color that an object appears to be is determined by the wavelength of light that reaches your eyes.
  1. The color of light that is reflected by an object is the color that reaches your eyes.
  1. If an object appears white it is reflecting all colors and absorbing none.
  1. If an object appears black, it is absorbing all colors and reflecting none.