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(i) According to Maxwell, an accelerated charge sets up a magnetic field in its neighbourhood. The magnetic field, in turn, produces an electric field in that region. Both these fields vary with time and act as sources for each other.
(ii) As oscillating charge is accelerated continuously, it will radiate electromagnetic waves continuously.
(iii) In 1988, Hertz demonstrated the production of electromagnetic apparatus is shown schematically in fig.
(iv) An induction coil is connected to two spherical electrodes with a narrow gap between them. It acts as a transmitter. The coil provides short voltage surges to the spheres making one positive and the other negative. A spark is generated between the spheres when the voltage between them reaches the breakdown voltage for air. As the air in the gap is ionised, it conducts more rapidly and the discharge between the spheres becomes oscillatory.
(v) The above experiment arrangment is equivalent to an LC circuit, where the inductance is that of the loop and the capacitance is due to the spherical electrodes.
(vi) Electromagnetic waves are radiated at very high frequency(=100 MHz) as a result of oscillation of free charges in the loop.
(vii) Hertz was able to detect these waves using a single loop of wire with its own spark gap (the receiver).
(viii) Sparks were induced across the gap of the receiving electrodes when the frequency of the receiver was adjusted to match that of the transmitter.
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