Experiment No. 2
Title: Verification of Bohr’s Postulates using the Frank-Hertz Experiment
Aim:
To verify Bohr’s theory of quantized energy levels in atoms by using the Franck-Hertz experiment with mercury vapor and observing inelastic collisions between electrons and atoms.
Apparatus Required:
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Frank-Hertz tube filled with mercury vapor
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Power supply with voltage control
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Ammeter and voltmeter
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Oven (to maintain mercury temperature)
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Oscilloscope or digital display
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Connecting wires and the stand
Theory:
According to Bohr’s postulates, electrons in an atom occupy discrete energy levels and absorb/emit energy only in fixed quanta. In the Frank-Hertz experiment, electrons are accelerated through mercury vapor. At certain voltages, electrons lose energy in inelastic collisions by exciting mercury atoms. This causes a drop in collector current, observable as peaks in the I-V curve.
Energy difference between peaks corresponds to the excitation energy of mercury (first excited state), typically around 4.9 eV.
Diagram (Descriptive):
(Use labelled diagram in practical notebook)
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A cylindrical Frank-Hertz tube is shown with cathode (heated filament), grid, and anode.
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Mercury vapor fills the tube.
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Variable voltage is applied between cathode and grid.
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The current between the grid and the anode is measured as electrons pass through.
Procedure:
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Connect the Frank-Hertz tube as per the standard setup.
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Heat the tube to the proper temperature (~175°C) to vaporize mercury.
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Gradually increase the accelerating voltage and note the collector current.
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Observe periodic drops in current, indicating inelastic collisions.
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Record the voltages corresponding to the current maxima.
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Calculate energy difference between consecutive peaks.
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Compare it with the theoretical excitation energy of mercury.
Observation Table:
| S. No. | Accelerating Voltage (V) | Collector Current (mA) | Observation |
|---|---|---|---|
| 1 | 4.9 | Peak 1 | First inelastic collision |
| 2 | 9.8 | Peak 2 | Second excitation peak |
| 3 | 14.7 | Peak 3 | Third peak |
| 4 | 19.6 | Peak 4 | Fourth peak |
Result:
The energy difference between two consecutive peaks is found to be approximately:
This matches the known first excitation energy level of mercury, confirming the quantized nature of atomic energy levels as proposed by Bohr.
Conclusion:
The Frank-Hertz experiment successfully verified Bohr’s postulates by demonstrating discrete energy absorption in mercury atoms. The presence of current drops at fixed voltages confirms the quantization of electron energy states.
BSc 2nd Year Chemistry Major 1 Important Questions 2025 —
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“नीम के पत्तों में छिपा है एंटीबैक्टीरियल गुणों का राज!”
क्या आप जानते हैं कि नीम (Azadirachta indica) के पत्ते न केवल स्वास्थ्य के लिए लाभकारी हैं, बल्कि बैक्टीरिया को भी मात देने की ताकत रखते हैं?
यह शोध, नीम के पत्तों से प्राप्त यौगिकों के प्रभावी एंटीबैक्टीरियल गुणों की गहरी जानकारी प्रदान करता है।
Dissertation Topic: “Neem (Azadirachta indica) के पत्तों से प्राप्त यौगिकों का एंटीबैक्टीरियल गुणों के लिए विश्लेषण”
यह शोध न केवल रसायन विज्ञान के क्षेत्र में नई जानकारी प्रस्तुत करता है, बल्कि प्राकृतिक उपचारों को वैज्ञानिक प्रमाणों के साथ जोड़ता है।
क्या आप भी नीम के गुणों पर आधारित नये उपचारों में रुचि रखते हैं?
यह Dissertation आपके ज्ञान को नई दिशा दे सकता है।
खरीदने के लिए यहाँ क्लिक करें:
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