Question
Thu February 24, 2011 By: Padmini Kommu

Pls explain breifly the hertz's experiment?

Expert Reply
Thu February 24, 2011

Dear student

Hertz experiment

The energy carried by electromagnetic radiation is derived from the kinetic energy of an oscillating charge. To get appreciable amount of radiation, the charge should oscillate to an extent comparable with the wavelength of the radiation. Hertz devised a system in which the charges oscillate with a frequency equal to 5 x 107 Hz, resulting in emission of electromagnetic radiation of wavelength nearly 6 m.

Hertz experimental set up consists of two copper or zinc plates P and P2 placed parallel to each other separated by a distance of 0.6 m (Fig. 4.2). These plates are connected to two well polished metal spheres A and B through thick copper wires. A high potential difference of several thousand volts is applied between the plates by using an induction coil.

The air in the small gap between A and B 2 to 3 cm) gets ionized due to high potential difference. This acts as a path for the discharge of the plates. A spark is produced between the spheres A and B. This results in a very high frequency (5 x 107 Hz) oscillations of charges on the plates. Thus a high frequency electric field is produced in the vertical gap between A and B, and a magnetic field of the same frequency is produced in the horizontal plane perpendicular to the gap between the spheres A and B. Electromagnetic waves consisting of these oscillating electric and magnetic fields are radiated from the spark gap. The wavelength of the radiations emitted is nearly 6 m.

Hertz also used a detector to detect the electromagnetic radiations produced in the experiment. Detector consists of an open metallic ring of diameter 0.7 m with small spheres C and D separated by a small gap. The ring is so arranged that it's plane is perpendicular the magnetic field produced by the oscillating charges. The oscillating magnetic field linked with the ring causes a large induced emf which results in a spark between the spheres C and D.

 
Hope this helps.
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