lenses & visible light

• how does a lens form an image?

  refracting light
• how does a convex lens form an image?

  parallel rays of light are brought to focus at the principal focus
• what is the focal length?

  distance from the lens to the principal focus
• what is the difference between the image produced by a convex & a concave lens?

  • convex lenses can produce real or virtual images
  • concave lenses can only produce virtual images
• what 3 things do u have to say to describe an image?

  • how big it is compared to the object
  • whether it's upright or inverted relative to the object
  • whether it's real or virtual
• what determines the colour of visible light waves

  wavelength & frequency of the light waves
• what is specular reflection?

  reflection of light from a smooth surface in a single direction
• what is diffuse reflection?

  reflection of light from a rough surface which causes scattering
• how would a red colour filter work?

  • absorb all wavelengths of light other than those in the red range of the spectrum
  • only red light transmitted by the filter
• what determines the colour of an opaque object?

  • different objects reflect different wavelengths of light by different amounts
  • the wavelengths that are most strongly reflected determine the colour
• what happens to wavelengths of light that aren't reflected by an opaque object?

  any wavelengths that aren't reflected are absorbed by the object
• what colour will the object appear if all wavelengths are reflected equally?

  white
• what colour will the object appear if all wavelenths are absorbed?

  black