Q.Mention the contribution of Indian physicist J.C. Bose in the production of electromagnetic waves.
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Start your 14-day free trial to unlock the full solution →J.C. Bose pioneered millimetre-wave generation and detection in the 1890s, demonstrating wireless signalling and key properties of EM waves before Marconi's work became widely known — his apparatus achieved wavelengths as short as 5 mm, a feat unmatched for decades.
The context: electromagnetic waves in the late 19th century
When Maxwell predicted electromagnetic waves theoretically in the 1860s and Hertz confirmed them experimentally in 1887–88, the race was on to generate, detect, and apply these waves. Hertz worked with decimetre-scale waves; the challenge was to push into shorter wavelengths (millimetre and microwave regions) and to harness them for communication. This is where Jagadish Chandra Bose made his mark.
Bose's pioneering contributions
1. Generation of millimetre waves (1894–1896)
Bose designed compact spark-gap oscillators and used them to generate electromagnetic waves with wavelengths as short as 5 mm (60 GHz). At the time, this was the shortest wavelength anyone had produced in a laboratory. He achieved this by miniaturising Hertz's apparatus: smaller gaps, tighter coupling, and innovative resonator designs.
The significance: moving from Hertz's ~60 cm waves to Bose's 5 mm waves opened the door to what we now call the microwave and millimetre-wave spectrum, critical for radar, satellite communication, and spectroscopy.
2. Detection using semiconductor junctions
Bose invented sensitive detectors for these high-frequency waves. His most famous device was a galena (lead sulphide) crystal detector — a point-contact semiconductor diode. When EM waves struck the junction, they rectified the oscillating signal into a measurable DC current.
This was the first practical use of a semiconductor in electronics, predating the widespread adoption of crystal radios by two decades. Bose's "coherer" was more reliable and sensitive than the metal-filings coherers used by Marconi.
3. Demonstration of wave properties
In public lectures in Calcutta (1895) and London (1896–97), Bose demonstrated:
- Reflection, refraction, and polarisation of millimetre waves using prisms and mirrors made of materials like sulphur and jute.
- Wireless signalling across a room, ringing a bell remotely by transmitting EM waves — a year before Marconi's famous demonstrations.
- Rotation of the plane of polarisation by twisted jute structures, analogous to optical activity.
He showed that these invisible waves obeyed the same laws as light, reinforcing Maxwell's unification of optics and electromagnetism.
4. Philosophical stance and lack of patents …
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