Defence · State PCS
The photoelectric effect was discovered in 1887 by:
Answer (Detailed Solution Below)View answer ▾Hide ▴
Answer: Option B — Heinrich Hertz
Detailed Solution
The photoelectric effect is the emission of electrons from the surface of a metal when light of a suitable frequency (usually ultraviolet or visible light of high frequency) falls on it. The emitted electrons are called photoelectrons.
In 1887, the German physicist Heinrich Rudolf Hertz, while carrying out experiments to produce and detect electromagnetic waves (radio waves), noticed that a spark jumped more easily across a gap between two metal electrodes when ultraviolet light shone on them. This was the first observation of the photoelectric effect, though Hertz did not explain it. His experiments also proved the existence of electromagnetic waves predicted by James Clerk Maxwell. The SI unit of frequency, the hertz (Hz), is named after him.
Later, Wilhelm Hallwachs (1888) and Philipp Lenard (1902) studied the effect in detail. Lenard found that the energy of the emitted electrons depends on the frequency of light, not its intensity, which could not be explained by the wave theory of light.
In 1905, Albert Einstein explained the photoelectric effect using Max Planck's quantum idea. He proposed that light consists of tiny packets of energy called photons (quanta), each with energy E = hν, where h is Planck's constant and ν is the frequency. When a photon strikes a metal surface, it gives all its energy to an electron. If the photon's energy is more than the work function (the minimum energy needed to remove the electron), the electron is emitted. Below a certain threshold frequency, no electrons are emitted, however bright the light. Einstein received the Nobel Prize in Physics in 1921 "for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect". Robert Millikan experimentally verified Einstein's equation in 1916.
Applications of the photoelectric effect include photocells (used in automatic doors, burglar alarms and light meters), solar cells, and image sensors in digital cameras.
Why not the other options?
- ✗Albert Einstein explained the effect in 1905.
J.J. Thomson discovered the electron in 1897.
Robert Millikan verified Einstein's equation experimentally and measured the charge of the electron.
Quick tip
Remember: Photoelectric effect = discovered by Hertz (1887), explained by Einstein (1905, photons, Nobel 1921), verified by Millikan (1916); used in photocells and solar cells.
💬 Discussions on this question
Ask a doubt ›Still stuck on this question? Ask our faculty and fellow students — answers appear here.
Ask a doubtMore Scientists, Inventions & Discoveries Questions
View all ›- Q1.The wave nature of matter (matter waves) was proposed by:
- Q2.Who is known as the 'Father of India's Space Programme'?
- Q3.Who is known as the 'Father of Radio'?
- Q4.Georg Simon Ohm formulated the relation V = IR (Ohm's law) in the year:
- Q5.What is the name of the artificial intelligence chatbot developed by OpenAI, which made headlines in 2023?
More General Knowledge Questions
- Q1.The techniques of Rasa and Bhava used in Indian classical dance trace their origin to which ancient text?Indian Dance Forms
- Q2.Lavani, Powada, Koli, Waghya Murali and Dhangari Gaja are folk dances of which state?Indian Dance Forms
- Q3.The one-act play associated with the Sattriya tradition of Assam is called:Indian Dance Forms
- Q4.Which dance form of Goa is known as the 'Warrior Dance'?Indian Dance Forms
- Q5.Manipuri dance is based on the Rasleela themes of:Indian Dance Forms
Scientists, Inventions & Discoveries — Preparation
This question tests your understanding of Scientists, Inventions & Discoveries, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers famous scientists and their contributions, major inventions and their inventors, important discoveries in physics, chemistry and biology, Indian scientists and their work, and Nobel Prizes in science. Questions commonly match an invention with its inventor (the telephone with Alexander Graham Bell, and the World Wide Web with Tim Berners-Lee), a discovery with its scientist (penicillin with Alexander Fleming), or an Indian scientist with their work, such as C. V. Raman and the Raman effect, for which he won the Nobel Prize in Physics in 1930. Practise the scientists, inventions and discoveries questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.