EMR / Lenses

    Electromagnetic Radiation

      Electromagnetic waves consist of fields of electric and magnetic energy that are oscillating perpendicularly to the direction of propagation of the wave. The electric and magnetic fields are in phase with each other and are also perpendicular to each other. Since the fluctuations are perpendicular to the direction of propagation, electromagnetic waves are transverse waves.

    Electromagnetic Spectrum

      Type of Radiation
      (in order of decreasing frequency)


      Approximate frequency


      Produced by radioactive decay; nuclear reactions

      ³1020 Hz


      Produced by deceleration of high-speed electrons, e.g. X-ray tube.


      Produced by electrons going from higher energy orbitals to lower higher energy orbitals

      Visible light

      Produced by electrons going from higher energy orbitals to lower higher energy orbitals, e.g. electric light bulb

      1014 Hz

      (heat waves)

      Produced by and causes movement of atoms and molecules, vibration of bonds. Used in IR spectroscopy.

      Microwaves (higher-frequency radio waves)

      Lower-frequency radio waves

      Used in NMR spectroscopy

      106 Hz


      Since electromagnetic waves are transverse, they can be polarized. This means that the electric field fluctuates along a single plane as opposed to fluctuating in every plane (for simplicity, the magnetic field component is ignored).

      A polarizing material placed in the path of a beam of unpolarized light will absorb the electric field components in a certain plane. The transmitted light will thus be polarized in the plane perpendicular to plane in which absorption is occurring. The intensity of the light transmitted is half the intensity of the light incident on the polarizing material.

    Disorders of Vision

      Scientific name of disorder

      Common name of disorder

      Basic problem




      Cannot focus on distant objects

      Diverging lenses



      Cannot focus on near objects

      Converging lenses

    Lens Aberrations



      Measures to reduce it

      Spherical aberration

      The rays from a single point on the object are not focused to a single point on the image.

      Use an aperture so that only rays close to the principal axis can pass through the lens. Or use 2 lenses instead of 1.

      Chromatic aberration

      Dispersion in the lens causes different colors to to be focused at different points along the principal axis.

      Use an achromatic lens (a converging and diverging lens in tandem). This combination rejoins separated colors.

Make a Free Website with Yola.