Overview
This lecture covers the Davisson-Germer experiment, which provided experimental proof for the wave nature of electrons, supporting de Broglie's hypothesis of matter waves.
de Broglie's Hypothesis
- In 1924, de Broglie proposed that all matter has both wave and particle characteristics.
- Electrons, like light, exhibit a dual particle-wave nature.
Davisson-Germer Experiment Setup
- Conducted by C.J. Davisson and L.H. Germer in 1927 to test the wave nature of electrons.
- Main apparatus: nickel crystal target, electron gun (with tungsten filament), detector, and galvanometer.
- The electron gun heats a tungsten filament using a low tension battery to produce electrons; a high tension battery accelerates them.
- The electron beam passes through a pinhole and strikes the nickel crystal.
- The detector moves on a circular scale to measure scattered electrons' intensity at different angles.
Experimental Procedure and Observations
- Electrons struck the crystal and scattered in all directions, behaving like waves.
- At specific angles, detectors recorded a peak in intensity (maximum), attributed to constructive interference.
- This intensity peak is a signature of wave-like behavior.
Analysis and Conclusions
- Intensity of scattering varies with the angle of scattering (φ).
- Graphs plotted showed a bump (peak) at φ = 50°, indicating maximum constructive interference.
- The peak becomes more pronounced with increasing accelerating voltage, reaching maximum at 54 V, then decreases at higher voltages.
- Results confirmed the wave nature of electrons, validating de Broglie's hypothesis.
Key Terms & Definitions
- de Broglie Hypothesis — Theory proposing all matter exhibits both wave and particle properties.
- Constructive Interference — Wave phenomenon where overlapping waves add to produce a higher amplitude.
- Electron Gun — Device that emits and accelerates electrons toward a target.
- Scattering Angle (φ) — The angle between the incident and scattered electron directions.
- Detector — Device measuring the intensity of scattered electrons.
Action Items / Next Steps
- Review graphs of electron intensity versus scattering angle for different accelerating voltages.
- Read about Bragg's law and its role in analyzing crystal diffraction patterns.