Physics Chapter on Electrons and X-Ray Tubes
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Questions and Answers

Who is credited with first measuring the charge of an electron?

  • Richard Feynman
  • Robert Millikan (correct)
  • George Stoney
  • James Chadwick

    • What is the process by which electrons are emitted from the surface of a heated metal called?

  • Electrolysis
  • Nuclear fission
  • Photoelectric effect
  • Thermionic emission (correct)

    • In a cathode ray tube, what causes the electrons to accelerate toward the anode?

  • The fluorescent screen
  • The heating coil
  • A magnetic field
  • A high potential difference (correct)

    • Which of the following best describes how the electron beam is controlled in a cathode ray tube?

    <p>By manipulating magnetic or electric fields</p> Signup and view all the answers

    Which of the following is NOT a typical application of a cathode ray tube?

    <p>Modern flat-screen computer monitor</p> Signup and view all the answers

    What is the primary role of the heating coil in a cathode ray tube?

    <p>To emit electrons via thermionic emission</p> Signup and view all the answers

    What is the smallest amount of electrical charge found in nature?

    <p>The charge of an electron</p> Signup and view all the answers

    What is the purpose of the fluorescent screen in a cathode ray tube?

    <p>To make the electron beam visible</p> Signup and view all the answers

    What is the primary mechanism by which electrons are released from the cathode in an X-ray tube?

    <p>Thermionic emission</p> Signup and view all the answers

    In an X-ray tube, what is the primary purpose of the high voltage applied between the cathode and the anode?

    <p>To accelerate the emitted electrons</p> Signup and view all the answers

    What material is commonly used for the anode in an X-ray tube, and why?

    <p>Tungsten, due to its high density and high melting point</p> Signup and view all the answers

    Why is lead shielding used in the construction of an X-ray tube?

    <p>To absorb most of the X-rays emitted in all directions</p> Signup and view all the answers

    Which of the following is NOT a property of cathode rays?

    <p>They are attracted towards a positive charge.</p> Signup and view all the answers

    Which of the following best describes the process of X-ray production in an X-ray tube?

    <p>High-energy electrons cause inner electron transitions in the target material</p> Signup and view all the answers

    What does one electron volt (eV) represent?

    <p>The energy gained by an electron when it is accelerated through a potential difference of one Volt.</p> Signup and view all the answers

    Which property of X-rays makes them useful in medical imaging?

    <p>Ability to cause ionization</p> Signup and view all the answers

    An electron's potential energy is given by $W=QV$. What is an alternative way this energy can be converted to?

    <p>Kinetic energy.</p> Signup and view all the answers

    In what way can X-ray production be regarded as the inverse of the photoelectric effect?

    <p>X-rays use electrons to create electromagnetic radiation, while the photoelectric effect uses electromagnetic radiation to release electrons</p> Signup and view all the answers

    What is the force experienced by an electron moving at right angles within a magnetic field?

    <p>$F = Bqv$</p> Signup and view all the answers

    Which of the following is NOT a typical application of X-rays?

    <p>Enhancing the colour of fabrics</p> Signup and view all the answers

    What is the primary hazard associated with X-ray exposure?

    <p>They can ionize atoms in the body, potentially leading to cancer</p> Signup and view all the answers

    How is the radius of the circular path of an electron moving in a magnetic field determined?

    <p>$r = mv/Bq$</p> Signup and view all the answers

    Who is credited with the discovery of the electron as a fundamental particle?

    <p>G.J. Stoney</p> Signup and view all the answers

    What phenomenon is described as the emission of electrons from a metal when electromagnetic radiation falls upon it?

    <p>The Photoelectric Effect.</p> Signup and view all the answers

    What did William Crookes famously develop related to the study of electrons?

    <p>The cathode ray tube</p> Signup and view all the answers

    In the photoelectric effect, what is the term for the energy that goes into liberating an electron from the metal?

    <p>Work function.</p> Signup and view all the answers

    What is the term used to describe the phenomenon where a hot object emits electrons?

    <p>Thermionic emission</p> Signup and view all the answers

    What determines whether a photon can release an electron in the photoelectric effect?

    <p>The photon's frequency.</p> Signup and view all the answers

    What is the energy unit 'eV' (electron volt) commonly used for in physics related to the electron?

    <p>To measure the energy of electrons, photons, and other particles</p> Signup and view all the answers

    Given the equation: Energy of incident photon = Energy required to free an electron + kinetic energy of the photo-electron, how can this be written using symbols?

    <p>$hf = \phi + \frac{1}{2}mv^2$</p> Signup and view all the answers

    In the photoelectric effect, what is the threshold frequency?

    <p>The minimum frequency of light required to release electrons from the metal.</p> Signup and view all the answers

    What notable discoveries occurred during the period roughly between 1895-1905?

    <p>X-rays, the electron, radioactivity, quantum mechanics, relativity</p> Signup and view all the answers

    What is the purpose of a photocell in a circuit?

    <p>It converts light energy into electrical energy.</p> Signup and view all the answers

    What is smallest unit of charge found in nature?

    <p>The charge on an electron</p> Signup and view all the answers

    What effect does increasing the intensity of light have on a photocell?

    <p>It increases the number of emitted electrons.</p> Signup and view all the answers

    Which of the following is NOT a typical application of photoelectric sensing devices?

    <p>Generating electricity in solar panels.</p> Signup and view all the answers

    How are X-rays produced in an X-ray tube?

    <p>By high-energy electrons colliding with a heavy metal target.</p> Signup and view all the answers

    What is the relationship between the photon’s energy (E), Planck's constant (h), and the frequency of the wave (f)?

    <p>$E = hf$</p> Signup and view all the answers

    What is the primary function of the electron gun in a cathode ray tube (CRT)?

    <p>To accelerate electrons towards the screen and vary their intensity</p> Signup and view all the answers

    In a color television CRT, what determines the color of a pixel?

    <p>The relative intensities of the three electron guns corresponding to the three primary colors</p> Signup and view all the answers

    If an electron is accelerated across a potential difference of V, which of the following correctly expresses the gain in kinetic energy?

    <p>$eV = ½ mv^2$</p> Signup and view all the answers

    What is the common unit used to measure electron energies, which is typically smaller than Joules?

    <p>Electron Volt</p> Signup and view all the answers

    When an electron moves perpendicular to a magnetic field, what type of path will it follow?

    <p>A circular path</p> Signup and view all the answers

    Which of the following correctly describes why an electron moving in a circle is accelerating?

    <p>Its direction is continually changing, even though its speed is constant.</p> Signup and view all the answers

    Who first proposed that light energy is quantized by introducing the idea of packets of light called photons?

    <p>Albert Einstein</p> Signup and view all the answers

    Which of the following best describes what is meant by quantization of energy?

    <p>Energy occurs in discrete packets.</p> Signup and view all the answers

    In the context of the photoelectric effect, what does the work function refer to?

    <p>The minimal energy to liberate an electron from a metal surface</p> Signup and view all the answers

    According to Einstein's description of the photon, what is a key characteristic of the energy of electromagnetic radiation?

    <p>It is made up of a finite number of energy quanta localized at points in space.</p> Signup and view all the answers

    In the photoelectric effect, where is the incident light energy absorbed by an electron?

    <p>At the surface of the metal</p> Signup and view all the answers

    What is the main difference between ionization energy and work function?

    <p>Ionization energy involves gases, whereas work function involves solids</p> Signup and view all the answers

    Which of these scientists first proposed that heat energy is quantized?

    <p>Max Planck</p> Signup and view all the answers

    About how many pixels are present on a screen of 640-by-480?

    <p>About 300,000 pixels</p> Signup and view all the answers

    What is one of the main factors that determines the quality of a television screen?

    <p>The speed at which the electron gun travels, and the number of pixels on the screen</p> Signup and view all the answers

    Which scientist is credited with initially proposing the idea of 'negatively charged corpuscles' smaller than hydrogen atoms?

    <p>J.J. Thompson</p> Signup and view all the answers

    What phenomenon did G.P. Thompson demonstrate regarding the nature of electrons?

    <p>The electron's wave-like nature through diffraction.</p> Signup and view all the answers

    What technology was used to determine the structure of DNA molecules?

    <p>X-ray crystallography</p> Signup and view all the answers

    What is the significance of the book, 'The Double Helix'?

    <p>It revealed the petty and competitive behind-the-scenes nature of scientific research.</p> Signup and view all the answers

    What is the purpose of the high voltage between the cathode and anode in a Cathode Ray Tube (CRT)?

    <p>To accelerate electrons towards the screen.</p> Signup and view all the answers

    What is the process by which electrons are emitted from a heated metal surface called?

    <p>Thermionic emission</p> Signup and view all the answers

    What happens to the energy of an electron when it strikes the screen of a CRT?

    <p>It is converted into heat and light.</p> Signup and view all the answers

    Which particle is emitted from a metal surface when light of a suitable frequency shines on it?

    <p>Electrons</p> Signup and view all the answers

    What is a photon?

    <p>A particle of light.</p> Signup and view all the answers

    What key aspect of light's nature did the quantum theory reveal?

    <p>That light exhibits both wave like and particle like behavior.</p> Signup and view all the answers

    In the context of electron diffraction, what role does carbon play?

    <p>It serves as a diffraction grating.</p> Signup and view all the answers

    The work function of a metal is typically measured in which energy unit?

    <p>Electron Volts (eV)</p> Signup and view all the answers

    According to the material, the term 'Big Bang' was:

    <p>a term created by a scientist in a derogatory fashion.</p> Signup and view all the answers

    In the context of X-ray crystallography, what did Bragg (Senior and Junior) use to determine the internal structure of various crystals?

    <p>X-rays</p> Signup and view all the answers

    Which of the following is most closely associated with the understanding of the wave behavior of the electron?

    <p>Electron diffraction.</p> Signup and view all the answers

    What is the phenomenon where light incident on a metal surface causes the emission of electrons?

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

    Which of the following is a practical application of the photoelectric effect?

    <p>Automatic doors</p> Signup and view all the answers

    What determines the energy of incident light in the context of the photoelectric effect?

    <p>Its frequency</p> Signup and view all the answers

    What is the term for a single packet of electromagnetic radiation?

    <p>Photon</p> Signup and view all the answers

    In the photoelectric effect, what does an increase in the intensity of light with sufficient energy cause?

    <p>An increase in the number of liberated electrons</p> Signup and view all the answers

    When ultraviolet light shines on a negatively charged zinc plate connected to an electroscope, what happens to the leaves of the electroscope?

    <p>The leaves fall together</p> Signup and view all the answers

    What is the work function energy in the analogy of the Photoelectric Effect?

    <p>The admission charge at the nightclub</p> Signup and view all the answers

    What term describes the minimum energy required to release an electron from the surface of a metal?

    <p>Work function</p> Signup and view all the answers

    Why does the gold leaf of a negatively charged electroscope collapse when ultraviolet radiation is shone on a zinc plate?

    <p>The ultraviolet radiation causes electrons to be emitted from the zinc, reducing the negative charge and allowing the leaves to collapse.</p> Signup and view all the answers

    According to the provided content, what is one limitation of using the nightclub analogy to explain the photoelectric effect?

    <p>Photons cannot redistribute energy among themselves, unlike the people with money in the analogy.</p> Signup and view all the answers

    What prevents the collapse of the gold leaf when a piece of ordinary glass covers the zinc during ultraviolet radiation exposure?

    <p>The glass blocks the ultraviolet radiation from reaching the zinc.</p> Signup and view all the answers

    How can X-ray radiation potentially harm a person's DNA?

    <p>By ionizing atoms, causing a disruption that can lead to altered cell messages such as cell division.</p> Signup and view all the answers

    If the energy of an incident photon exceeds the work function of a metal, what does the excess energy become?

    <p>Kinetic energy of the emitted electron</p> Signup and view all the answers

    Which of the following statements correctly describes the early views of Max Planck on light?

    <p>He agreed that light was emitted as a continuous wave.</p> Signup and view all the answers

    What is the primary reason why ordinary glass absorbs ultraviolet light?

    <p>Its molecular structure absorbs UV</p> Signup and view all the answers

    Why does illuminating the zinc with green light not cause the gold leaf to collapse?

    <p>Green light does not possess the necessary energy to initiate the photoelectric effect in zinc.</p> Signup and view all the answers

    If the electroscope is positively charged with no UV light, why do the leaves not collapse when zinc is attached?

    <p>The leaves of a positively charged electroscope do not collapse when electrons are emitted.</p> Signup and view all the answers

    Why does green light typically not cause photoemission from a zinc plate?

    <p>Green light has insufficient frequency/energy</p> Signup and view all the answers

    What was Einstein's initial reaction to the idea that nuclear events are governed by probabilities?

    <p>He rejected the idea, stating that 'God does not play dice'.</p> Signup and view all the answers

    What 'fudge factor' did Einstein introduce into his equations for General Relativity, and why?

    <p>To stabilize the predicted universal expansion, since he believed the universe was static</p> Signup and view all the answers

    In a photocell, what occurs at the cathode (A) when light falls upon it?

    <p>Electrons are emitted from the cathode.</p> Signup and view all the answers

    In a photoelectric experiment, what happens when the electroscope is positively charged?

    <p>Electrons are attracted back and the electroscope remains charged</p> Signup and view all the answers

    If the frequency of incident radiation is below the threshold frequency, what will not occur?

    <p>The photoelectric effect</p> Signup and view all the answers

    What happened to Einstein's reputation near the end of his career?

    <p>He lost respect for failing to unite the four forces of Nature using his approach, instead using probability</p> Signup and view all the answers

    How does increasing the brightness of the light incident on the photocell impact the current in the circuit?

    <p>The current increases.</p> Signup and view all the answers

    What is the general relationship between the intensity of light and the current produced in a photocell, when the frequency is above threshold?

    <p>Directly proportional</p> Signup and view all the answers

    What is the name given to the process where electrons are emitted from the surface of a hot metal?

    <p>Thermionic emission</p> Signup and view all the answers

    Which of the following statements is true regarding the liberation of electrons in the Photoelectric Effect?

    <p>A photon needs to have at least the same energy as the work function to liberate an electron, any extra will be the kinetic energy of the electron.</p> Signup and view all the answers

    What type of electromagnetic radiation is used in X-ray machines?

    <p>X-rays</p> Signup and view all the answers

    What is the primary role of the high voltage across an X-ray tube?

    <p>To attract and accelerate electrons towards the target.</p> Signup and view all the answers

    What observation led to the conclusion that light acts like a particle?

    <p>The behavior of light in the photoelectric effect.</p> Signup and view all the answers

    What would happen if you increased the intensity of light that does not have enough energy to liberate an electron using the photoelectric effect?

    <p>It would result in no electrons being liberated.</p> Signup and view all the answers

    What physical property allows X-rays to be used to detect flaws in metals?

    <p>Penetration ability</p> Signup and view all the answers

    Which material is commonly used for the target in an X-ray tube?

    <p>Tungsten</p> Signup and view all the answers

    In an X-ray tube, what is the primary purpose of the high voltage applied between the anode and cathode?

    <p>To accelerate electrons towards to anode</p> Signup and view all the answers

    What happens to the majority of the electron's energy when it hits the target in an X-ray tube?

    <p>It is converted into heat.</p> Signup and view all the answers

    Which scientist is credited with realizing that light behaves like a particle?

    <p>Albert Einstein</p> Signup and view all the answers

    In addition to being ionizing, what did the given text suggest the use of X-rays were used for?

    <p>To determine the size and shape of patients' feet.</p> Signup and view all the answers

    Why is a lead shield typically placed around an X-ray tube?

    <p>To prevent X-rays from escaping in all directions.</p> Signup and view all the answers

    Why is tungsten commonly used as the target material in X-ray tubes?

    <p>High melting point</p> Signup and view all the answers

    Which of the following describes how electrons are produced at the cathode of an X-ray tube?

    <p>By heating a filament, causing thermionic emission.</p> Signup and view all the answers

    What alternative end of the universe was mentioned, that may cause Einstein's 'fudge factor' to not be a mistake?

    <p>The universe may start to contract instead of expanding, resulting in a 'Big Crunch'.</p> Signup and view all the answers

    How do X-rays differ from light rays?

    <p>X-rays and light are both electromagnetic waves, but X-rays have higher energy, shorter wavelengths, and greater penetrating power.</p> Signup and view all the answers

    What is the relationship between X-ray production and the photoelectric effect?

    <p>X-ray production is the converse of the photoelectric effect, where kinetic energy of electrons changes to produce wave energy.</p> Signup and view all the answers

    What occurs at the filament (A) within an X-ray tube?

    <p>The filament is heated causing thermionic emission of electrons.</p> Signup and view all the answers

    Study Notes

    The Electron

    • The electron is a useful theoretical concept in understanding the natural world.
    • Richard Feynman, a Nobel Prize-winning physicist, stated this.
    • Electrons orbit the nucleus.
    • They have a very small mass.
    • They have a negative charge.
    • The charge on an electron is the smallest unit of charge found in nature.
    • Robert Millikan first measured the charge of the electron.
    • George Stoney coined the term "electron."
    • Thermionic emission is the release of electrons from a hot metal's surface.

    Cathode Ray Tube (CRT)

    • A CRT uses a heated cathode (thermionic emission) to create a beam of electrons.
    • High voltage accelerates the electrons toward the anode.
    • Electrons passing through the anode hole hit the fluorescent screen, producing a visible image.
    • Electric and magnetic fields can deflect the electron beam.
    • CRTs are used in oscilloscopes, televisions, and computers (now obsolete).
    • Cathode rays are high-speed electron beams (a stream of electrons).
      • Travel in straight lines.
      • Cause substances to fluoresce.
      • Deflected by electric/magnetic fields.
      • Produce X-rays when striking heavy metals.

    Energy Associated with an Electron

    • An electron's potential energy (W) is calculated using the formula W = QV.
    • The electronvolt (eV) is a smaller unit of energy at the atomic level.
    • 1 eV is the energy lost or gained by an electron accelerating through 1 volt.
    • 1 eV = 1.6 × 10−19 Joules.
    • An electron's potential energy converts to kinetic energy (W = ½ mv2).
    • Moving electrons in a magnetic field follow a circular path

    Magnetic Fields and Electrons

    • A beam of electrons moving perpendicular to a magnetic field is bent into a circular path.
    • Formula for force F = Bqv, where e is the electron charge.
    • Force is always perpendicular to the velocity.
    • Formula is derived from F=mv^2/r.
    • Knowing the other variables allows the radius of the path to be calculated.

    The Photoelectric Effect

    • The photoelectric effect is the emission of electrons from a metal when light shines on it.
    • A suitable frequency is required for the effect to occur.
    • Demonstrated using a negatively charged electroscope and zinc plate.
    • UV light causes the leaves to collapse.
    • Einstein proposed photons as discrete energy packets.
      • Photons are absorbed by electrons.
      • Some energy is used to remove the electron.
      • The remainder becomes kinetic energy of the ejected electron.
    • This "proved" light has a particle property.
    • The energy of a photon is calculated using E = hf (where h is Planck's constant and f is the frequency).

    The Photocell

    • A photocell uses the photoelectric effect to convert light into an electrical current.
    • Light striking the cathode releases electrons.
    • Electrons flow through the circuit, detectable by a galvanometer or activating electronic devices.
    • Increasing the light intensity increases the number of electrons and, correspondingly the current.

    X-Rays

    • X-rays are produced when high-energy electrons collide with a dense target, usually tungsten.
      • Most of the kinetic energy gets converted to heat and must be removed by cooling.
      • Inner electrons are excited to higher energy levels, and then return to lower levels.
      • Energy is released as X-rays.
    • X-rays are electromagnetic waves with high penetration.
    • X-rays are used in medicine and industry for various purposes (e.g., detecting broken bones).
    • X-ray production is the inverse of the photoelectric effect. Electrons are used to produce electromagnetic radiation.

    Hazards of X-Rays

    • X-rays can cause atom ionization in the body.
    • This can lead to DNA damage and potentially cancer.
    • Appropriate safety precautions must always be taken when working with X-rays.

    Quantum Theory

    • Planck and Einstein proposed that energy can be quantized in discrete packets.
    • Einstein's theory predicted the photoelectric effect.
    • Quantum physics involves probability and uncertainty in the outcomes of specific experiments.

    Electron Diffraction and Waves

    • Electrons, like light, can exhibit wave-like behavior (de Broglies wave length).
    • Certain arrangements can be diffracted or interfere.
    • This wave-particle duality was demonstrated in experiments.

    Additional Information

    • Protons and neutrons are additional subatomic particles.
    • The photoelectric effect contrasts with thermionic emission, which involves electrons from a hot metal.

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    Description

    Test your knowledge on the fundamental concepts of electrons and their applications in technologies like cathode ray tubes and X-ray tubes. This quiz covers key topics such as electron charge measurement, emission processes, and the role of various components within these devices. Dive into the physics behind electron behavior and interactions!

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