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    Workfunction Guide

    Uploaded by

    Muhammad Hashir
    This document describes an experiment to determine the work function of a tungsten filament using a Guard Ring Diode tube. It provides background theory on thermionic emission and the Richardson-Dushman equation. The procedure involves taking measurements of anode current and filament temperature at varying filament voltages. A graph of ln(current) vs 1/temperature is plotted and the slope is used to calculate the experimental work function. The expected value is around 2 eV.

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd

    Workfunction Guide

    Uploaded by

    Muhammad Hashir
    130 views3 pages
    This document describes an experiment to determine the work function of a tungsten filament using a Guard Ring Diode tube. It provides background theory on thermionic emission and the Richardson-Dushman equation. The procedure involves taking measurements of anode current and filament temperature at varying filament voltages. A graph of ln(current) vs 1/temperature is plotted and the slope is used to calculate the experimental work function. The expected value is around 2 eV.

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    This document describes an experiment to determine the work function of a tungsten filament using a Guard Ring Diode tube. It provides background theory on thermionic emission and the Richardson-Dushman equation. The procedure involves taking measurements of anode current and filament temperature at varying filament voltages. A graph of ln(current) vs 1/temperature is plotted and the slope is used to calculate the experimental work function. The expected value is around 2 eV.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    130 views3 pages

    Workfunction Guide

    Uploaded by

    Muhammad Hashir
    This document describes an experiment to determine the work function of a tungsten filament using a Guard Ring Diode tube. It provides background theory on thermionic emission and the Richardson-Dushman equation. The procedure involves taking measurements of anode current and filament temperature at varying filament voltages. A graph of ln(current) vs 1/temperature is plotted and the slope is used to calculate the experimental work function. The expected value is around 2 eV.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 3

    Dr.

    Farah Aziz PHY-2101P Lab III

    Experiment: Find the Work Function of a Tungsten


    filament using a Guard Ring Diode (GRD-7)
    tube.
    Theory
     Work function
    o Definition
     Types of electron emission
    o Photo electric emission
     Definition
    o Field emission
     Definition
    o Secondary emission GRD-7 Tube
     Definition
    o Thermionic emission
     Definition
     Detailed description
     Richardson-Dushman equation
    𝐼𝐴 = Anode Current
    2 −
    o = (original form of the law)
    𝑇 = Temperature of the filament in Kelvins
    We modify it to the following form
    k = Boltzmann constant = 1.38 × 10−23 J/K
    1
    ln 2 = ln 𝜑 = work function in electron Volts
    k
    𝑒 = Charge on an electron = 1.602 × 10−19 C

    y-axis
    x-axis
    slope

     Types of Cathodes
    o Directly Heated Cathode
    o Indirectly Heated Cathode 𝑅𝑓
    = Resistance of the filament at temperature 𝑇(℃)
     Finding Temperature from Resistance
    𝑅0 = Resistance of the filament at zero ℃
    o = 0 (1 ) = 0.28 𝛺

    𝛼 = Temperature coefficient of resistance


    = 0.0045℃−1

    𝑇 = Temperature of the filament in ℃


    Dr. Farah Aziz PHY-2101P Lab III

    −
    So that temperature in ℃ is given as: = (℃)
    Temperature in Kelvin = ( in ℃) 273
     Guard Ring Diode (GRD-7) Tube
     Procedure
    Remember to write the reference/source after each
    article!!
    filament

    Anode

    Guard Rings
    RingsRings

    Observations and Calculations


    =
    0
    273 1⁄
    = 0 ln ( 2
    )

    Filament Filament Filament Filament Anode


    voltage current resistance temperature Current
    (V) (A) (Ω) (K) (µA) K −1

    Here, = 0.0045 C−1 and 0 = 0.28 Ω.

     Take more than 10 readings.


    Dr. Farah Aziz PHY-2101P Lab III

     Plot a graph between


    ln ( ) (-y axis) and 1⁄ (+x axis). The graph should be a Straight line, with a negative
    slope
    −
     Find the slope of the Straight line using the formula i.e. = .
    −
     The experimental value of the work function in eV is proportional to the slope.
     Use the formula
    ×
    = = eV
     The expected value of the work function is around 2 eV

    1⁄ (K −1 )
    𝑇  Remember your graph must have
    +x axis
    SALT!!
    ln ( 2 )
    𝐼𝑎𝑛

    SALT
    𝑇

    Scale Title
    Axes Label
    -y axis

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