Heinrich Hertz

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Heinrich Hertz

Hertz, in 1886, constructed a series of experiments to verify J.C. Maxwell’s predictions on the electromagnetic spectrum.

Heinrich Hertz's First Transmitter from 1886

The instrument used by Hertz incorporated an induction coil to produce an extremely high voltage. This was connected to a circuit with a very small opening, with small copper balls on each end. Capacitor plates were used to adjust the capacity of the circuit for resonance. A ring of copper wire with a small gap, also edged with spark balls placed at varying distances, up to a few hundred metres away. When the power was turned on, small sparks were produced in the opening. This proved Maxwells theory about electromagnetic wave propagation. Hertz also unknowingly demonstrated the photoelectric effect during his experiments.

Hertz demonstrated that these new electromagnetic waves could be reflected from a metal mirror, and that they could be refracted, through passing them through a prism made of pitch. In both cases the detector was placed such that it could only have detected the waves if they had been bent, through refraction or reflection.

To measure the wavelength, two beams of waves were sent, one directly to a detector, and another reflected from a zinc plate 12m from the source, to the detector. The detected waves interfere both constructively and destructively and, from this pattern, the wavelength was calculated, at approximately four metres. Using this, and the frequency of oscillation in the circuit he gained a measurement for the speed of the waves using the universal wave equation, v = λ.f. The speed was 3 x 108 ms-1, close to the values estimated by Maxwell (3.11 x 108 ms-1) and measured by Fizeau (3.15 x 108 ms-1) for the speed of light.

Hertz also demonstrated that the waves could be polarized, through rotating the detector ring, which sparked when parallel to the transmitter, and didn’t when perpendicular to the same. At the smaller angles...
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