Explain Hertz experiment for generation of electro-magnetic waves.


Hertz experiment is based on the principle that an oscillating electric charge radiates electro-magnetic waves.


It consists of two large square metal plates P1 and P2 placed about 60 cm apart. The plates are connected to two highly polished metal spheres S1 and S2 through thick copper wires. An induction coil is employed to supply high potential difference across the spheres.


When a high potential difference is applied across S1 and S2, the air between the spheres gets ionized and electromagnetic waves of high frequency is radiated. This generated em-wave is detected using a detector placed at a distance from the spheres. The frequency of oscillation is given by the equation

where, L is the inductance of the coil and C is the capacitance of the two plates P1 and P2

The detector is a metal ring connected to two small spheres C and D with a small gap in between. The detector is placed in such an alignment that the magnetic field produced by the oscillating charge (current) is perpendicular to the plane of the ring. The spark produced between S1 and S2 radiates em waves and as a spark is initiated between C and D.


  • The electromagnetic radiation produced by this experiment is significant only if the distance to which the charge oscillates is comparable to the wavelength of radiation.
  • The frequency of these oscillations is 5 x 107 Hz.
  • Wavelength of the obtained radiation is 6 m.
  • The resistance of the metal ring, of the detector, is of low resistance.

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