Plz explain what experiment did sir Marconi did with Hertz experiment how he set up apparatus ?(plz explain this with diagram)and how did it worked??how were em waves generated and detected across English channel.
 

Asked by upmaniousagarika | 30th Jul, 2016, 05:56: PM

Expert Answer:

Marconi's experiment was deeply inspired by Hertz experiment of electromagnetic waves.
 
Hertz Experiment:
  • A high voltage power source caused sparks to oscillate across the gap . 
  • The visible spark is actually a series of many small sparks, jumping rapidly back and forth (oscillating) between the terminals.
  • The size of the metal plates attached to the spheres from which the sparks are produced, controls the frequency of the sparks produced.
  • A loop of wire held near the oscillating spark, had a spark jump across the air gap between the ends of the wire whenever a spark jumped across the high voltage (induction coil) spark gap.
  • Hertz reasoned that as the spark jumps back and forth across the gap of the induction coil, it must set up rapidly changing electric and magnetic fields. 
  • Hertz called the waves radio waves
  • Marconi used these waves to build the first radios.

Marconi's Modifications with Hertz experiment setup:


 (First radio transmitter)


 

  • At first Marconi used a transmitter to ring a bell in a receiver in his attic laboratory. 
  • He replaced Hertz’s vertical dipole with a vertical wire topped by a metal sheet, with an opposing terminal connected to the ground.
  • On the receiver side, Marconi replaced the spark gap with a metal powder coherer, a detector developed by Edouard Branly and other experimenters.
  • Marconi transmitted radio signals for about 1.5 miles (2.4 km) at the end of 1895.
  • Marconi found that much greater range could be achieved after he raised the height of his antenna
  • Inspired from a technique used in wired telegraphy, grounding his transmitter and receiver.
  • With these improvements the system was capable of transmitting signals up to 2 miles (3.2 km) and over hills.
  • The monopole antenna reduced the frequency of the waves compared to the dipole antennas used by Hertz, and radiated vertically polarized
  • radio waves which could travel longer distances.
  • By this point, he concluded that a device could become capable of spanning greater distances, with additional funding and research, and would prove valuable both commercially and militarily.
  • Marconi's experiment on 13 May 1897, Marconi sent the world's first ever wireless communication over open sea.
  • The experiment, based in Wales, witnessed a message transversed over the Bristol Channel from Flat Holm Island to Lavernock Point in Penarth, a distance of 6 kilometres (3.7 mi).
  • The message read "Are you ready"

 

(Magnetic Detector used by Marconi)

Key components of Marconi's experimental setup

  • A relatively simple oscillator or spark-producing radio transmitter
  • A wire or metal sheet capacity area suspended at a height above the ground
  • A coherer receiver, which was a modification of Edouard Branly's original device with refinements to increase sensitivity and reliability
  • A telegraph key to operate the transmitter to send short and long pulses, corresponding to the dots-and-dashes of Morse code
  • and A telegraph register activated by the coherer which recorded the received Morse code dots and dashes onto a roll of paper tape.

Answered by Abhijeet Mishra | 1st Aug, 2016, 01:28: PM