Physics · Class 12 Science
Ch 14Dual Nature of Radiation and Matter — Class 12 Physics, concept-first.
Every optical phenomenon studied so far in this course -- reflection, refraction, interference, diffraction, and polarization -- was explained by treating light as an electromagnetic wave: a pair of mutually perpendicular, oscillating electric and magnetic fields, both perpendicular to the direction of travel.
Key concepts
Hover a concept to preview it and jump to its most relevant Q&A.
Einstein's Photoelectric Equation
Building directly on Planck's quantization idea, Einstein in 1905 proposed that light of frequency should itself be thought of as a stream of discrete energy quanta (photons), each carrying energy .
Most relevant Q&A
- Explain the inverse linear dependence of stopping potential on the incident wavelength in a photoelectric effect experiment.Free
- It is observed in an experiment on photoelectric effect that an increase in the intensity of the incident radiation does not change the maxi…Free
- Polychromatic (containing many different frequencies) radiation is used in an experiment on photoelectric effect. The stopping potential (A)…Free
- Observations from an experiment on photoelectric effect for the stopping potential by varying the incident frequency were plotted. The slope…Free
- The threshold wavelength of tungsten is $2.76\times10^{-5}$ cm. (a) Explain why no photoelectrons are emitted when the wavelength is more th…Free
In previous exams
How often this chapter’s concepts have been examined — real appearance data, never estimated.
Chapter contents
The NCERT structure, section by section. Open a section to see its questions, then read the concept-first solution.
Introduction
Every optical phenomenon studied so far in this course -- reflection, refraction, interference, diffraction, and polarization -- was explained by treating light as an electromagnetic wave: a pair of m…
The Photoelectric Effect
In 1887, Heinrich Hertz was experimenting with the production of electromagnetic waves using a spark discharge when he noticed something unrelated to his main investigation: when ultraviolet light fel…
Experimental Set-up of Photoelectric Effect
To study the photoelectric effect quantitatively, experimenters built an evacuated glass tube fitted with a quartz window (quartz, unlike ordinary glass, transmits ultraviolet light without absorbing…
Observations from Experiments on Photoelectric Effect
Careful experiments with the apparatus of the previous section, carried out over several decades, established a set of very specific facts about the photoelectric effect.
Failure of Wave Theory to Explain the Observations from Experiments on Photoelectric Effect
Nearly every one of the nine observations of the previous section is flatly contradicted by the predictions of classical (wave) theory. The most damning failure concerns TIME.
Einstein's Postulate of Quantization of Energy and the Photoelectric Equation
Building directly on Planck's idea that energy comes in discrete packets, Einstein proposed in 1905 that under certain conditions light itself behaves as if made of localized PARTICLES of energy, whic…
Wave-Particle Duality of Electromagnetic Radiation
The photoelectric effect showed that light interacts with matter as if it were made of discrete energy packets -- photons.
Photo Cell
The PHOTOCELL is a practical device that puts the photoelectric effect to direct use, converting incident light energy into an electrical (current) signal.
De Broglie Hypothesis
In 1924, Prince Louis de Broglie made a striking proposal based purely on an argument from symmetry in nature.
Davisson and Germer Experiment
The Davisson-Germer experiment, performed in 1927 (with an independent confirmation by G. P. Thomson in 1928 using a different method), provided the first direct experimental proof of de Broglie's mat…
Wave-Particle Duality of Matter
If every moving material object has an associated de Broglie wavelength, a natural question arises: why do we never notice a 'wavelength' for a running child, or a moving car, in everyday life? The an…
Long Answer Questions
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- Q11Explain the inverse linear dependence of stopping potential on the incident wavelength in a photoelectric effect experiment.Free
- Q12It is observed in an experiment on photoelectric effect that an increase in the intensity of the incident radiation does not change the maxi…Free
- Q13Explain what do you understand by the de Broglie wavelength of an electron. Will an electron at rest have an associated de Broglie wavelengt…Preview
- Q14State the importance of Davisson and Germer experiment.Preview
Sample & Board Papers
Sample papers and previous-year board questions for this subject.
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- Q1The energy of a photon of wavelength $\lambda$ is ______. [h = Planck's constant, c = speed of light in vacuum] (A) $hc\lambda$ (B) $\dfrac{…Preview
- Q2In a photon-electron collision ______ (a) only total energy is conserved. (b) only total momentum is conserved. (c) both total energy and to…Preview
- Q3The momentum associated with photon is given by ____. (a) $h\nu$ (b) $h\nu/c$ (c) $hE$ (d) $h\lambda$Preview
- Q4Calculate the de-Broglie wavelength of an electron moving with one fifth of the speed of light. Neglect relativistic effects. ($h = 6.63 \ti…Preview
- Q5An electron of energy 150 eV has wavelength of $10^{-10}$ m. The wavelength of a 0.60 keV electron is (a) 0.50 Å (b) 0.75 Å (c) 1.2 Å (d) 1.…Preview
- Q6What is photoelectric effect? Define (i) Stopping potential, (ii) Photoelectric work function.Preview
- Q7Define ; (a) Threshold frequency (b) Photoelectric work functionPreview
- Q8The photoelectric work function for a metal surface is $3.84 \times 10^{-19}$ J. If the light of wavelength 5000 Å is incident on the surfac…Preview
- Q9Is it always necessary to use red light to get photoelectric effect?Preview
- Q10Explain de Broglie wavelength. Obtain an expression for de Broglie wavelength of wave associated with material particles. The photoelectric…Preview
- Q11If the maximum kinetic energy of emitted electrons in photoelectric effect is 2 eV, the stopping potential will be ______. (a) 0.5 V (b) 1.0…Preview
- Q12An electron is accelerated through a potential difference of 100 volt. Calculate de-Broglie wavelength in nm.Preview
- Q13With neat labelled circuit diagram, describe an experiment to study the characteristics of photoelectric effect.Preview
- Q14If the frequency of incident light falling on a photosensitive material is doubled, then kinetic energy of the emitted photoelectron will be…Preview
- Q15In a photoelectric experiment, the stopping potential is 1.5V. What is the maximum kinetic energy of a photoelectron?Preview
- Q16Define photoelectric effect and explain the experimental set-up of photoelectric effect.Preview
- Q17An electron, a proton, an α-particle and a hydrogen atom are moving with the same kinetic energy. The associated de-Broglie wavelength will…Preview
- Q18State Einstein's photoelectric equation and mention physical significance of each term involved in it. The wavelength of incident light is 4…Preview
- Q19If the frequency of incident radiation is increased above threshold frequency, keeping intensity and potential constant then the photoelectr…Preview
- Q20A metal surface is illuminated by photons of energy 5 eV and 2.5 eV respectively. The ratio of their wavelengths of emitted radiation is ___…Preview
- Q21Obtain an expression for the de-Broglie wavelength associated with an electron accelerated from rest through a potential difference of V vol…Preview
More questions
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- Q6What is photoelectric effect?Free
- Q7Can microwaves be used in the experiment on photoelectric effect?Free
- Q8Is it always possible to see photoelectric effect with red light?Preview
- Q9Using the values of work function given in Table 14.1, tell which metal will require the highest frequency of incident radiation to generate…Preview
- Q10What do you understand by the term wave-particle duality? Where does it apply?Preview
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- Q1A photocell is used to automatically switch on the street lights in the evening when the sunlight is low in intensity. Thus it has to work w…Free
- Q2Polychromatic (containing many different frequencies) radiation is used in an experiment on photoelectric effect. The stopping potential (A)…Free
- Q3An electron, a proton, an α-particle and a hydrogen atom are moving with the same kinetic energy. The associated de Broglie wavelength will…Preview
- Q4If $N_{Red}$ and $N_{Blue}$ are the number of photons emitted by the respective sources of equal power and equal dimensions in unit time, th…Preview
- Q5The equation E = pc is valid (A) for all sub-atomic particles (B) is valid for an electron but not for a photon (C) is valid for a photon bu…Preview
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- Q15What will be the energy of each photon in monochromatic light of frequency $5\times10^{14}$ Hz?Free
- Q16Observations from an experiment on photoelectric effect for the stopping potential by varying the incident frequency were plotted. The slope…Free
- Q17The threshold wavelength of tungsten is $2.76\times10^{-5}$ cm. (a) Explain why no photoelectrons are emitted when the wavelength is more th…Free
- Q18Photocurrent recorded in the micro ammeter in an experimental set-up of photoelectric effect vanishes when the retarding potential is more t…Preview
- Q19Radiation of wavelength 4500 Å is incident on a metal having work function 2.0 eV. Due to the presence of a magnetic field B, the most energ…Preview
- Q20Given the following data for incident wavelength and the stopping potential obtained from an experiment on photoelectric effect, estimate th…Preview
- Q21Calculate the wavelength associated with an electron, its momentum and speed (a) when it is accelerated through a potential of 54 V, [Ans: 0…Preview
- Q22The de Broglie wavelengths associated with an electron and a proton are same. What will be the ratio of (i) their momenta (ii) their kinetic…Preview
- Q23Two particles have the same de Broglie wavelength and one is moving four times as fast as the other. If the slower particle is an α-particle…Preview
- Q24What is the speed of a proton having de Broglie wavelength of 0.08 Å?Preview
- Q25In nuclear reactors, neutrons travel with energies of $5\times10^{-21}$ J. Find their speed and wavelength.Preview
- Q26Find the ratio of the de Broglie wavelengths of an electron and a proton when both are moving with the (a) same speed, (b) same energy and (…Preview