Light and Objects

Introduction

• Objects are classified by what they do to light:
  • Opaque: does not allow light to pass through; all light is either absorbed or reflected.
  • Translucent: can be seen through, but not clearly; allows some light to go through, but some is also absorbed or reflected
  • Transparent: allows almost all light to go through, so can be seen through clearly

Why Do Objects Appear Colored?

• All non-luminous objects which are colored appear so due to the fact that they absorb part of the incident radiation and reflect or transmit the remaining part to the observer; colors seen are those not absorbed.
• Transparent colorless objects: transmit all wavelengths of the visible spectrum (no absorbance); water, glass.
• Transparent colored objects: transmit only certain wavelengths of visible light and absorb the rest.
  • The color seen from the other side of the object is the color of this object.
  • Piece of red glass, when exposed to white light will transmit red and absorb all other colors.
• Opaque white and black objects: they appear white when they mainly reflect all the wavelengths of visible light. (colorless when light is transmitted, white when it is reflected).
  • Ideal black object: absorbs all visible light (opaque to visible light).
  • Absorbed light converted mainly to heat.
  • Grey object: partial absorbance and partial reflection of all frequencies of visible light.
• Opaque colored objects: objects (opaque or transparent)) have their colors because they selectively absorb all other colors except their own (this is the only color that is left unabsorbed).
  • When the light wave strikes an object, it interacts with that object’s electrons, and the greater mobility of electrons, the greater the degree of interaction.
  • As a result, metals interact with light differently than non-metals.

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