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.
11.3 PHOTOELECTRIC EFFECT
The photoelectric effect is the emission of electrons from a metal surface when illuminated by light of suitable frequency. Discovered by Heinrich Hertz in 1887 during electromagnetic wave experiments, he observed that ultraviolet light enhanced spark discharges. When light falls on a metal surface, electrons near the surface absorb energy from the incident radiation, overcoming the attraction of positive ions and escaping as photoelectrons. Wilhelm Hallwachs and Philipp Lenard further investigated this effect between 1886 and 1902. Lenard observed that ultraviolet radiation on an evacuated tube's emitter plate caused current flow due to emitted electrons attracted to a positively charged collector plate. Hallwachs showed that a negatively charged zinc plate lost charge when illuminated by UV light, indicating emission of negatively charged electrons. They also found a threshold frequency below which no electrons were emitted, depending on the metal. Metals like zinc, cadmium, and magnesium respond only to ultraviolet light, while alkali metals like lithium and sodium respond even to visible light. This phenomenon is called the photoelectric effect, involving conversion of light energy into electrical energy.
🔗 Connection: Leads to experimental study of photoelectric effect and its characteristics.
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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