  The charge to mass (e / m) ratio of the            Photoelectric Cell
   particles in anode rays depends upon the
   nature of the gas taken in the discharge              Photoelectric cell or photocell, device
   tube.                                                  whose electrical characteristics (e.g.,
  It travels in straight line.                           current, voltage, or resistance) vary when
                                                          light is incident upon it.
  It consists of fast moving positively
   charged particle.                                     The most common type consists of two
                                                          electrodes separated by a light-sensitive
  It deflected in magnetic field and electric
                                                          semiconductor material.
   field.
                                                         A battery or other voltage source
  It penetrates through the thin aluminum
                                                          connected to the electrodes sets up a
   foil.
                                                          current even in the absence of light; when
  It rays can produce fluorescence and
                                                          light strikes the semiconductor section of
   phosphorescence.
                                                          the photocell, the current in the circuit
X-Rays (X-radiation)                                      increases by an amount proportional to the
                                                          intensity of the light.
  X-rays are electromagnetic waves and part
   of the electromagnetic spectrum.                   Photoelectric Effect
  Roentgen discovered the X-rays.
                                                      It occurs when matter emits electrons upon
  Its wavelength shorter than that of                exposure to electromagnetic radiation, such as
   ultraviolet radiation, which is less than          photons of light. It is the ejection of electrons
   about 1 × 10 -8 meters.                            from a metal plate when light falls on it.
Properties of X-rays                                  Uses of Photoelectric Cell
These properties make X-rays very useful for          A photocell can be used in any situation where
medical diagnosis and treatment.                      beam of light falling on it is interrupted or
  they have a very short wavelength (about           broken by any mean.
   the same size as the diameter of an atom              To count vehicles passing a road.
  they cause ionisation (adding or removing             To count items running on a conveyer belt.
   electrons in atoms and molecules)
                                                         To open doors automatically in a building
  they affect photographic film in the same              such as banks or other commercial
   way as visible light (turning it black)                buildings or offices.
  they are absorbed (stopped) by metal and              To operate burglar alarms.
   bone
                                                         To produce sound in movies.
  they are transmitted by (pass through)
   healthy body tissue
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