Physics Chapter 11: Dual Nature of Radiation and Matter
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Questions and Answers

How does the maximum kinetic energy of photoelectrons relate to the frequency of incident radiation?

  • Decreases linearly with the frequency.
  • Increases linearly with the frequency. (correct)
  • Varies quadratically with the frequency.
  • Is independent of the frequency.

What is the role of the threshold frequency in the photoelectric effect?

  • It varies inversely with the intensity of the incident radiation.
  • It is the frequency that maximizes photoelectric emission.
  • It is the minimum frequency required for photoelectric emission. (correct)
  • It has no impact on photoelectric emission.

Which material is mentioned as being more sensitive to light in terms of photoelectric effect?

  • Selenium (correct)
  • Iron
  • Copper
  • Zinc

What happens to photoelectric emission when the frequency of incident radiation exceeds the threshold frequency?

<p>Emission starts instantly. (C)</p> Signup and view all the answers

What is the relationship between photoelectric current and intensity of incident light?

<p>Directly proportional when above threshold frequency. (A)</p> Signup and view all the answers

What characterizes the stopping potential in photoelectric experiments?

<p>Is independent of the intensity of incident radiation. (D)</p> Signup and view all the answers

What effect does ultraviolet light have on copper in terms of the photoelectric effect?

<p>Causes immediate photoelectric emission. (D)</p> Signup and view all the answers

What happens to photoelectric emission if the frequency of the incident radiation is lower than the cut-off frequency?

<p>No photoelectric emission occurs regardless of intensity. (D)</p> Signup and view all the answers

What does the photoelectric equation imply about the relationship between energy and frequency?

<p>Energy is directly proportional to frequency. (D)</p> Signup and view all the answers

In the wave nature of light, which phenomenon is NOT typically associated with it?

<p>Photoelectric effect (C)</p> Signup and view all the answers

What variables are included in the equation $l = \frac{hc}{eV0 + f0}$?

<p>Planck's constant and speed of light (C), Energy and work function (D)</p> Signup and view all the answers

What is the wave-particle duality in the context of light phenomena?

<p>Light exhibits both particle and wave properties depending on the experiment. (A)</p> Signup and view all the answers

What role does Planck's constant play in the photoelectric equation?

<p>It relates energy to frequency. (A)</p> Signup and view all the answers

In which situation does the wave description of light become more crucial?

<p>When measuring the wavelength of light. (A), In the absorption of light by rods and cones of the eye. (B)</p> Signup and view all the answers

What is the significance of the wavelength calculated using the formula in the content?

<p>It represents the color of the light. (A)</p> Signup and view all the answers

How does wave-particle duality apply to other particles, according to the content?

<p>All particles such as protons and neutrons also exhibit wave-like behavior. (B)</p> Signup and view all the answers

What occurs when ultraviolet light falls on the emitter plate C?

<p>Electrons are ejected and flow towards the collector plate A. (A)</p> Signup and view all the answers

What phenomenon was observed by Hallwachs when a negatively charged zinc plate was illuminated by ultraviolet light?

<p>The zinc plate lost its negative charge and became positively charged. (B)</p> Signup and view all the answers

What is the threshold frequency in the context of ultraviolet light and electron emission?

<p>It is the minimum frequency required for electron emission from an emitter plate. (A)</p> Signup and view all the answers

Which types of metals are sensitive only to ultraviolet light for electron emission?

<p>Metals like zinc, cadmium, and magnesium. (A)</p> Signup and view all the answers

What was the significant discovery related to electrons made in 1897?

<p>Electrons are released from materials when light is absorbed. (D)</p> Signup and view all the answers

What types of light can alkali metals like lithium and potassium respond to for electron emission?

<p>Both visible and ultraviolet light. (A)</p> Signup and view all the answers

What term is used to refer to the electrons emitted due to light exposure?

<p>Photoelectrons. (B)</p> Signup and view all the answers

What effect does increasing the intensity of ultraviolet light have on the photo current observed?

<p>It increases the amount of photo current generated. (D)</p> Signup and view all the answers

What is the reason the wave picture fails to explain the photoelectric emission?

<p>Electrons do not absorb energy continuously. (A), Photoelectric emission is delayed. (C)</p> Signup and view all the answers

What does Einstein's photoelectric equation describe?

<p>The maximum kinetic energy of emitted photoelectrons. (B)</p> Signup and view all the answers

In Einstein's model, what is the energy of each quantum of radiation related to?

<p>Frequency of light and Planck's constant. (B)</p> Signup and view all the answers

If the energy of a single photon exceeds the work function of a metal, what happens to the electron?

<p>It is emitted with maximum kinetic energy. (B)</p> Signup and view all the answers

What distinguishes the wave-picture from the photon-picture of the photoelectric effect?

<p>The stopping potential's dependence on frequency (B)</p> Signup and view all the answers

How does increasing the intensity of light affect photoelectric emission?

<p>It increases the number of emitted electrons per second. (C)</p> Signup and view all the answers

Which equation correctly represents the relationship between wavelength and momentum of a matter wave?

<p>$ u = \frac{h}{p}$ (C)</p> Signup and view all the answers

What is the relationship between the energy of a photon and its frequency?

<p>Energy is directly proportional to frequency. (C)</p> Signup and view all the answers

What is implied if an electron does not escape the metal surface despite absorbing energy?

<p>The absorbed energy is less than the work function. (B)</p> Signup and view all the answers

What does the term 'maximum kinetic energy' refer to in the context of photoemission?

<p>Energy carried by the photon minus the work function (C)</p> Signup and view all the answers

Which statement correctly describes the energy absorption process in the wave picture?

<p>Absorption occurs continuously over the wavefront affecting all electrons equally. (D)</p> Signup and view all the answers

Which of the following factors affects the stopping potential in a photoelectric experiment?

<p>The work function of the material (B)</p> Signup and view all the answers

What physical significance does the phase velocity of a matter wave hold?

<p>It has no physical significance (D)</p> Signup and view all the answers

What is the minimum wavelength of emitted X-rays produced by 30 kV electrons?

<p>$\frac{12.4}{30}$ pm (C)</p> Signup and view all the answers

What is needed to find the momentum of each photon emitted by a helium-neon laser producing light of wavelength 632.8 nm?

<p>The frequency and the speed of light (A)</p> Signup and view all the answers

What does the slope of the cut-off voltage versus frequency graph represent in a photoelectric effect experiment?

<p>Planck's constant (D)</p> Signup and view all the answers

What is the significance of the slope in the $V_0$ versus $n$ curve according to the photoelectric equation?

<p>It is directly proportional to Planck's constant. (B)</p> Signup and view all the answers

What was Millikan's primary objective during his experiments on the photoelectric effect?

<p>To disprove Einstein's photoelectric equation. (B)</p> Signup and view all the answers

In the context of the photoelectric effect, what does the symbol $f_0$ represent in Einstein's equation?

<p>The work function of the material. (A)</p> Signup and view all the answers

What role did Planck's constant, $h$, play in Millikan's experiments?

<p>It was calculated from measurements, validating Einstein's equations. (C)</p> Signup and view all the answers

How did the research performed by Millikan contribute to the field of theoretical physics?

<p>It validated the predictions made by Einstein's theory. (A)</p> Signup and view all the answers

What is implied by the critical analysis of the foundations of quantum mechanics outlined in the content?

<p>Ongoing debates and investigations refine the understanding of quantum phenomena. (B)</p> Signup and view all the answers

What phenomenon does Eq.(11.2) represent in the context of the photoelectric effect?

<p>The relationship between energy and frequency of photons. (A)</p> Signup and view all the answers

Which element's photoelectric effect did Millikan specifically measure in his experiments?

<p>Sodium (B)</p> Signup and view all the answers

Flashcards

Photoelectric Effect

The emission of electrons from a metal surface when light shines on it.

What happens when UV light falls on an emitter plate?

Electrons are ejected from the emitter plate, creating a current flow.

Threshold Frequency

The minimum frequency of light required to cause electron emission from a material.

What happens below the threshold frequency?

No electrons are emitted, regardless of the light intensity.

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How does the threshold frequency relate to the material?

The threshold frequency is specific to the material; different materials have different thresholds.

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What happens to the photocurrent as the collector plate potential increases?

The photocurrent increases until it reaches a saturation point, beyond which further increase in potential does not increase the current.

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How does the photocurrent change with light intensity?

The photocurrent is directly proportional to the intensity of the incident light.

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Photoelectrons

Electrons emitted from a metal surface due to the photoelectric effect.

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Kinetic energy of photoelectrons

The energy of the emitted electrons, which depends on the frequency of the incident light.

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Intensity of incident light

The brightness of the light, essentially the number of photons per second.

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Photoelectric current

The flow of emitted electrons in a circuit due to the photoelectric effect.

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Stopping potential

The voltage needed to stop the most energetic photoelectrons from reaching the collector.

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Relationship between intensity and current

The photoelectric current is directly proportional to the intensity of the incident light.

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Relationship between intensity and stopping potential

The stopping potential is independent of the intensity of the incident light.

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Wave Picture of Energy Absorption

In the wave picture, energy is absorbed continuously by an electron over the entire wavefront of radiation. This absorption occurs gradually over time and involves numerous electrons.

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Photoelectric Emission: Wave vs. Quantum

The wave picture suggests gradual energy absorption, taking time for electrons to escape. However, observation shows photoelectric emission is instantaneous. This contradicts the wave picture.

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Einstein's Photoelectric Equation

Einstein proposed that electromagnetic radiation consists of discrete energy packets called quanta. Each quantum has energy (hν), where h is Planck's constant and ν is frequency.

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Quantum Energy Absorption

In the photoelectric effect, an electron absorbs a single quantum of energy (hν) from the radiation. If this energy exceeds the work function, the electron is emitted.

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Work Function (f0)

The minimum energy an electron needs to escape from a metal surface. It's a property of the metal.

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Maximum Kinetic Energy of Emitted Electron

The maximum kinetic energy of an emitted electron is determined by the difference between the energy of the absorbed quantum (hν) and the work function (f0). This is represented by Kmax = hν - f0.

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Light Intensity and Electron Emission

Increasing the intensity of light of a given frequency increases the number of photons incident per second, leading to more electrons being emitted per second.

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Maximum Kinetic Energy vs. Intensity

The maximum kinetic energy of emitted electrons is determined by the energy of each photon (hν), not by the intensity of light.

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Photoelectric Equation

An equation describing the relationship between the energy of a photon (hn), the work function (f0) of a material, and the kinetic energy of the emitted electron (eV0).

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Work Function

The minimum energy required to remove an electron from the surface of a material.

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Photon

A tiny packet of electromagnetic energy, acting as a particle.

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Wave-Particle Duality

The concept that light and matter exhibit both wave-like and particle-like properties.

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Interference

The superposition of waves resulting in a pattern of constructive and destructive interference.

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Diffraction

The bending of waves around obstacles or through narrow openings.

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Polarization

The restriction of the oscillations of a wave to a specific plane.

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Compton Effect

The scattering of X-rays by electrons, resulting in a decrease in energy of the X-rays.

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What does the photoelectric effect tell us about light?

The photoelectric effect demonstrates that light interacts with matter in discrete units of energy, called photons, with energy proportional to the frequency of the light. This suggests that light has particle-like properties.

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What is the significance of stopping potential?

The stopping potential is the minimum negative voltage applied to the collector plate that stops all photoelectrons from reaching it. It is directly proportional to the frequency of incident light and independent of light intensity.

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What is the difference between wave and particle picture of light?

The wave picture of light considers it as a continuous wave, while the photon picture describes light as composed of discrete energy packets called photons. The photoelectric effect supports the photon picture.

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What is the significance of group velocity?

The group velocity of a matter wave is physically meaningful and corresponds to the actual velocity of the particle. This contrasts with its phase velocity, which is not physically significant.

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What is the maximum frequency of X-rays?

The maximum frequency of X-rays produced by electrons accelerated through a potential difference is directly proportional to the potential difference. It's calculated by: f = eV/h, where e is the electron charge, V is the potential difference, and h is Planck's constant.

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What is the maximum Kinetic Energy of photoelectrons?

The maximum kinetic energy of photoelectrons emitted from a metal surface is determined by the energy of the incident photons (hf) and the work function of the metal (Φ), given by: KE = hf – Φ.

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What is the stopping potential?

The stopping potential (Vâ‚€), for a given frequency of incident light, is the negative potential difference applied to the collector plate that brings the photoelectric current to zero. It is related to the maximum kinetic energy of photoelectrons by eVâ‚€ = KE.

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What is the photoelectric equation?

Einstein's equation that describes the relationship between the energy of a photon (hν), the work function (f0) of a material, and the kinetic energy of the emitted electron (eV0): eV0 = hν - f0

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What is the relationship between intensity of incident light and photocurrent?

The photocurrent is directly proportional to the intensity of the incident light.

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How does the stopping potential vary with the intensity of incident light?

The stopping potential is independent of the intensity of the incident light.

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Study Notes

Chapter Eleven: Dual Nature of Radiation and Matter

  • Introduction: Maxwell's equations and Hertz experiments established the wave nature of light. Electricity conduction through gases at low pressure led to discoveries like X-rays (Roentgen) and electrons (Thomson). Electrons were found to be fundamental constituents of matter.

  • Electron Emission: Metals have free electrons responsible for conductivity. Electrons escape from a metal's surface if they gain enough energy (work function). This minimum energy can be supplied via thermionic emission (heating), field emission (strong electric field) or photoelectric emission (light).

  • Photoelectric Effect:

    • Hertz's Observations: Hertz observed enhanced high voltage sparks when illuminated with ultraviolet light.
    • Hallwachs and Lenard's Observations: Confirmed photoemission, showing current flow when ultraviolet light struck an emitter plate. Current stopped when light stopped. Current varied with collector plate potential and light intensity.
    • Threshold Frequency: A minimum frequency of light is needed to emit electrons. Light with lower frequency won't cause emission.
    • Instantaneous Emission: Emission occurs immediately, even with dim light.

  • Experimental Study of Photoelectric Effect:

    • Arrangement: An evacuated glass/quartz tube with a photosensitive plate (emitter) and a collector plate. A battery varies the potential difference between the plates.
    • Intensity Variation: Current increases linearly with light intensity. Saturation current occurs when all emitted electrons are collected.
    • Potential Variation: Current increases with increasing collector potential, reaching saturation when all emitted electrons are collected. Stopping potential (Vo) is the minimum negative potential needed to stop emitted electrons.

  • Effect of Intensity of Light on Photocurrent: Photocurrent increases linearly with light intensity. The number of photoelectrons emitted per second is directly proportional to the intensity of light.

  • Effect of Potential on Photoelectric Current: Increasing the positive potential on the collector increases the current. When the collector potential is negative enough, photoelectric current goes to zero. The stopping potential (Vo) corresponds to a negative potential where no electron reach the collector.

  • Effect of Frequency on Stopping Potential: The stopping potential increases linearly with the frequency of incident light (above the threshold frequency)

    • Maximum Kinetic Energy = Stopping Potential x electron charge

  • Einstein's Photoelectric Equation: Proposed that light was composed of discrete units (photons) with energy hν (where h is Planck's constant and ν is frequency). Electrons absorb a photon's energy, and if it's high enough, the electron escapes (maximum kinetic energy = hν - Φ (where Φ is the work function).

  • Particle Nature of Light (Photons): Light has a dual nature: wave and particle. Momentum of light is hv/c, where c is the speed of light. Photons carry energy and momentum.

  • De Broglie Wavelength: Matter (e.g., electrons) can exhibit wave-like properties. The de Broglie wavelength of a particle is given by λ = h / momentum.

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Dual Nature of Radiation And Matter PDF

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Explore the fascinating concepts of the dual nature of radiation and matter in this quiz based on Chapter Eleven. Discover how Maxwell's equations and early experiments led to the understanding of electrons and the photoelectric effect. Test your knowledge of electron emission and the pivotal experiments of Hertz and others.

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