Dual Nature of Radiation and Matter | Class 12 Physics Notes
By ConceptScroll Team · Published on 17 July 2026 · 2 min read
Dual Nature of Radiation and Matter – this guide gives you a concise, exam-ready overview of Dual Nature of Radiation and Matter from Class 12 Physics, written by ConceptScroll editors and reviewed against the latest NCERT textbook.
11.1 INTRODUCTION
The late 19th century witnessed significant progress in understanding light and atomic structure. Maxwell's equations of electromagnetism predicted electromagnetic waves, and Hertz experimentally generated and detected these waves in 1887, firmly establishing the wave nature of light. Concurrently, studies on electric discharge through gases at low pressure in discharge tubes led to landmark discoveries such as X-rays by Roentgen in 1895 and the electron by J. J. Thomson in 1897. When a discharge occurs at very low pressure (~0.001 mm of mercury), a fluorescent glow appears on the glass opposite the cathode, with color depending on the glass type. This glow was attributed to radiation from the cathode, known as cathode rays, discovered by William Crookes in 1870 and later suggested to be streams of fast-moving negatively charged particles. J. J. Thomson experimentally measured the speed and charge-to-mass ratio (e/m) of these particles using perpendicular electric and magnetic fields. The speed was about 0.1 to 0.2 times the speed of light (3 × 10^8 m/s), and the e/m value was 1.76 × 10^11 C/kg, independent of cathode material or gas type, indicating universality. Around the same time, metals irradiated by ultraviolet light or heated emitted negatively charged particles with the same e/m ratio, confirming these particles as electrons, fundamental constituents of matter. Millikan's oil-drop experiment in 1913 precisely measured the electron charge as 1.602 × 10^-19 C, establishing quantization of electric charge. Knowing charge and e/m allowed determination of electron mass. These discoveries laid the foundation for modern atomic physics.
🔗 Connection: Leads to the study of electron emission mechanisms from metals and the photoelectric effect.
Frequently asked questions
The minimum energy required for the electron emission from the metal surface can be supplied to the free electrons by which of the following physical processes?
All the above
When photons of energy, h v fall on an aluminium plate having work function ø o , photoelectrons of maximum kinetic energy K are ejected. If the frequency of radiation is doubled, the maximum kinetic energy of the ejected photoelectrons will be
K + h v
In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by
increasing the potential difference between the anode and the filament
With the increase in the intensity of incident radiation, the
photoelectric current increases
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