Instrumental Analysis: Spectrophotometry Lecture 2
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Questions and Answers

What is the primary function of an absorption filter in spectrophotometry?

  • It filters light based on wavelength alone.
  • It reflects all incident light.
  • It enhances the intensity of all colors.
  • It absorbs undesired light and transmits desired light. (correct)
  • In which region of the spectrum is an absorption filter primarily used?

  • Ultraviolet region
  • Visible region (correct)
  • Infrared region
  • Radio frequency region
  • Which characteristic does NOT describe an absorption filter?

  • It selectively transmits desired wavelengths.
  • It can be used outside the visible region. (correct)
  • It reduces the intensity of undesired light.
  • It is specific to certain wavelengths of light.
  • What occurs to the light that is absorbed by an absorption filter?

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

    What would be the outcome if an undesired part of the light spectrum is transmitted instead of absorbed?

    <p>The measurement will be inaccurate and contaminated with noise.</p> Signup and view all the answers

    What is the primary function of the detector mentioned?

    <p>To alternate between the sample and reference beams</p> Signup and view all the answers

    How does the detector operate concerning the chopper?

    <p>It synchronizes its measurements with the chopper's movements</p> Signup and view all the answers

    What does the reference beam allow the detector to do?

    <p>It enables background correction of measurements</p> Signup and view all the answers

    What is meant by 'synchronism' in the context of the detector's operation?

    <p>Coordinating measurements with the chopper</p> Signup and view all the answers

    When measuring the beam, what role does the chopper play?

    <p>It divides the measurement process into time intervals</p> Signup and view all the answers

    What is the primary function of the beam splitter in a double-beam spectrophotometer?

    <p>To split the light beam into two separate beams.</p> Signup and view all the answers

    What occurs after the light beam passes through the monochromator in a double-beam spectrophotometer?

    <p>It is split into two separate beams.</p> Signup and view all the answers

    What role does the chopper play in the double-beam spectrophotometer?

    <p>It blocks one beam at a time.</p> Signup and view all the answers

    Which statement best describes the arrangement of components in the double-beam spectrophotometer?

    <p>A single beam is measured against the reference beam sequentially.</p> Signup and view all the answers

    What is the significance of using a double-beam system in spectrophotometry?

    <p>It helps in reducing fluctuations that may affect measurement accuracy.</p> Signup and view all the answers

    What are the two types of cuvettes mentioned?

    <p>Glass and Plastic cuvettes</p> Signup and view all the answers

    Which type of cuvette is suitable for use in the visible region?

    <p>Both Glass and Plastic cuvettes</p> Signup and view all the answers

    Which statement best describes the application of the glass cuvette?

    <p>Used in the visible region only</p> Signup and view all the answers

    What is the primary limitation of plastic cuvettes?

    <p>They are less durable than glass cuvettes</p> Signup and view all the answers

    In which type of study is a cuvette most commonly used?

    <p>Spectrophotometric analysis</p> Signup and view all the answers

    What are the main components of the described device?

    <p>Photo-emissive cathode and collecting anode</p> Signup and view all the answers

    What occurs when the beam of light interacts with the cathode?

    <p>It emits electrons in proportion to the light intensity</p> Signup and view all the answers

    What is the role of the anode in this context?

    <p>To collect emitted electrons from the cathode</p> Signup and view all the answers

    Which of the following statements is true regarding the interaction between the cathode and light?

    <p>The emitted electrons move towards the anode due to attraction</p> Signup and view all the answers

    Which statement correctly describes the relationship between light intensity and electron emission?

    <p>Electrons are emitted in the same quantity as light intensity</p> Signup and view all the answers

    What role do the dynodes play in a photomultiplier?

    <p>They provide increasing positive potential to amplify the signal.</p> Signup and view all the answers

    What is the source of electrons in a photomultiplier?

    <p>Cathode after exposure to light.</p> Signup and view all the answers

    What process is utilized in the generation of electrons in a photomultiplier?

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

    How are the dynodes configured in a photomultiplier?

    <p>In a series with gradually increasing positive potential.</p> Signup and view all the answers

    What occurs at the dynodes when electrons are present in the photomultiplier?

    <p>Electrons cause the release of additional electrons.</p> Signup and view all the answers

    Study Notes

    Spectrophotometry Lecture Notes

    • Course: Instrumental Analysis (PMC-205)
    • Level: II
    • Semester: 3
    • Topic: Spectrophotometry (Lecture 2)
    • Instructor: Dr. Rania El-Shaheny

    Key Learning Objectives

    • Identify the basic components of a spectrophotometer.
    • Describe the types and properties of each spectrophotometer component.
    • Compare and contrast UV and visible spectrophotometers.

    Spectrophotometer Components

    • Light Source: Necessary for stable and intense light over a broad wavelength range. Two main types:

      • Tungsten lamp: Used for visible light.
      • Deuterium lamp: Used for UV light.
    • Wavelength Selector (Monochromator): Isolates a specific wavelength of light from a broad spectrum. Three types:

      • Filters: Selection based on filtering undesirable wavelengths. Two types:
        • Absorption filters: Absorb unwanted wavelengths, transmit desired ones (used in visible region only).
        • Interference filters: Reflect unwanted wavelengths, transmit desired ones (used in both visible and UV regions).
      • Prisms: Separate light into beams of different wavelengths using refraction. Two types:
        • Glass prisms: Used in the visible region only (opaque to UV light).
        • Quartz prisms: Used in both visible and UV regions.
      • Gratings: Highly polished surface with parallel, equally spaced grooves. Two types:
        • Reflection gratings: Reflect light at different angles based on wavelength (most common).
        • Transmission gratings: Transmit light at different angles based on wavelength.
    • Sample Compartment & Cuvette: Holds the sample to be analyzed. Two types:

      • Glass or plastic cuvettes: Used for visible light only.
      • Quartz cuvettes: Used for both visible and UV light.
    • Detector: Measures the amount of light passing through to generate an electrical signal. Two common types:

      • Phototubes: Emit an electric current when exposed to light.
      • Photomultipliers: Multiply the initial electrons emitted from a photocathode, allowing for detection of very weak light.
    • Readout device: Converted the signal from the detector to a readable form, either transmittance or absorbance.

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    Description

    Test your understanding of Spectrophotometry from the Instrumental Analysis course. This quiz covers the components of a spectrophotometer, the types of light sources, and the comparison between UV and visible spectrophotometers. Perfect for students in their third semester.

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