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Introduction

  • Course Title: Physics for Biotechnologies

  • Module: Quantum Phenomena: Photoelectric Effect

  • Instructor: Dr. Anshu Awasthi

  • Institution: Chandigarh University, Uttar Pradesh

  • Course Code: 25PYH-109

Course Outcomes (COs) &

  • After completion of this course, the learners will be able to:

    • CO1: Comprehend the principles of wave optics, interference, and diffracti - on (Bloom’s Level 2)

    • CO2: Describe the operation of lasers and optical fibers and analyze their use in biomedical applications (Bloom’s Level 4)

    • CO3: Apply quantum principles and atomic models to interpret spectroscopy and mass spectrometry data (Bloom’s Level 3)

    • CO4: Demonstrate the working of semiconductor devices and explain the application of XRD in crystallography (Bloom’s Level 3)

    • CO5: Analyze the structures at the nanoscale based on their properties for various applications (Bloom’s Level 4)

CO Mapping

  • This lecture is mapped with CO3 emphasizing the application of quantum principles and atomic models to interpret spectroscopy and mass spectrometry data.

Program Outcomes (POs)

  • After completion of the program, learners will be able to:

    • PO1: Engineering Knowledge: Apply knowledge of mathematics, science, engineering fundamentals, and specialization to solve complex engineering problems.

    • PO2: Problem Analysis: Identify, formulate, and analyze complex engineering problems, reaching substantiated conclusions using fundamentals of mathematics and sciences.

    • PO3: Design/Development of Solutions: Design solutions for complex engineering problems considering public health, safety, and cultural, societal, and environmental factors.

    • PO4: Conduct Investigations: Conduct research-based investigations into complex problems, including experimental design, data analysis, and synthesis of information for valid conclusions.

    • PO5: Modern Tool Usage: Create, select, and apply appropriate techniques, resources, and technological tools for complex engineering activities.

    • PO6: The Engineer and Society: Assess societal, health, safety, legal, and cultural issues regarding professional engineering practice.

    • PO7: Environment and Sustainability: Recognize the need for sustainability in engineering solutions within societal contexts.

    • PO8: Ethics: Apply and commit to ethical principles and responsibilities in engineering practice.

    • PO9: Individual and Team Work: Function effectively as an individual and as a team member or leader in diverse settings.

    • PO10: Communication: Communicate effectively regarding complex engineering activities in diverse audiences.

    • PO11: Project Management and Finance: Apply engineering management principles to work as a member or leader in project management.

    • PO12: Life-long Learning: Engage in independent and lifelong learning in the context of technological change.

CO-PO Mapping

  • Mapping of Course Outcomes to Program Outcomes:

    • CO1: 3, 2

    • CO2: 3, 2, 2

    • CO3: 3, 2, 2, 2

    • CO4: 2, 2, 2

    • CO5: 2, 3, 2

Topics Covered

  • Quantum Phenomena: Photoelectric Effect

Overview of Classical Mechanics

  • Failure of Classical Mechanics includes phenomena such as:

    • Photoelectric Effect

    • Blackbody Radiation

    • Compton Scattering

    • Stability of Atoms

    • Spectral Distribution of Blackbody Radiation

    • Origin of Discrete Spectra of Atoms

  • Classical mechanics successfully explains the motion of celestial bodies, macroscopic and microscopic terrestrial bodies moving at non-relativistic speeds.

Photoelectric Effect

Experimental Arrangement

  • Components:

    • Vacuum Tube (A)

    • Metallic Plate (B)

    • Charge Collecting Plate (C)

    • Galvanometer (G)

    • Potential Difference (V)

    • Photoelectric Current (ie)

    • Ejected Electrons (empty circle)

    • Direction of Moving Electrons (filled arrows)

Experimental Findings

  • Findings Related to Photoelectric Effect:

    • Result 1: Photoelectric current (ie) increases with the increasing intensity (I) of incident radiation at a constant frequency (ν). -

    • Result 2: The stopping potential (V0) refers to potential required to make the current (ie) cease (ie = 0).

    • Result 3: Emission of electrons occurs only if the frequency of incident radiation is higher than the threshold frequency (ν0).

    • Result 4: The maximum kinetic energy (EK) of photoelectrons is independent of the intensity (I) of the incident light.

    • Result 5: The maximum kinetic energy of ejected photoelectrons depends on the frequency of the incident radiation.

Classical Physics Explanation

  • Issues with Classical Physics:

    • No Time-lag: Classical theory suggests time delay for electron ejection due to wave energy distribution over many electrons.

    • Photocurrent vs. Intensity: An increase in intensity alters amplitude without affecting the number of emitted electrons, contrary to experimental findings.

  • Threshold Frequency Explanation: Classical physics state that any incident radiation can eventually emit electrons if given enough time, regardless of frequency.

  • Kinetic Energy vs. Frequency: Increasing frequency should increase kinetic energy, but traditional theory violates this by suggesting no impact on electron number.

Quantum Mechanics Explanation

  • Explanation with Quantum Mechanics:

    • No Time-lag: Each photon moves at speed of light carrying specific energy. Photons give all energy to a single electron, resulting in immediate ejection.

    • Photocurrent vs. Intensity: Higher light intensity results in more ejected photoelectrons directly proportional to photon count.

  • Threshold Frequency: There exists a minimum frequency below which no emissions can occur; energy of photons relates to work function (φ) and ejected electrons' kinetic energy.

  • Kinetic Energy vs. Frequency: Increasing frequency enhances the kinetic energy of emitted electrons.

Conclusions

  • Classical mechanics cannot explain atomic-level phenomena leading to the development of quantum mechanics, which accounts for peculiar behaviors in microscopic phenomena like the photoelectric effect and Compton scattering.

Further Readings

  • Malik, H. K., & Singh, A. K. (2018). Engineering Physics.

  • Muktavat, K., & Upadhyaya, A. K. (2010). Applied Physics. IK International Pvt Ltd.

References

  • Young, H. D., Freedman, R. A., & Ford, A. L. (2008). Sears and Zemansky's University Physics (Vol. 3). Pearson Education.

Video Links

  • nptelhrd. (2008, December 17). Lecture - 1 Introduction to Quantum Physics; Heisenberg’s Uncertainty Principle [Video]. YouTube. Retrieved July 18, 2025, from https://www.youtube.com/watch?v=TcmGYe39XG0

  • Academic Lesson. (2021, October 21). Quantum Physics Full Course | Quantum Mechanics Course [Video]. YouTube. Retrieved July 18, 2025, from https://www.youtube.com/watch?v=hyctIDPRSqY

  • nptelhrd. (2013, March 4). MOD-01 LEC-01 Quantum Mechanics -- An Introduction [Video]. YouTube. Retrieved July 18, 2025, from https://www.youtube.com/watch?v=pGerRhxNQJE

List of Figures

  • Figure 1: Experimental arrangement (Malik, H. K., & Singh, A. K. (2018). Engineering Physics)

  • Figure 2: Positive potential to collecting plate.

  • Figure 3: Negative potential to collecting plate.

  • Figure 4: Role of intensity on photoelectric current.

  • Figure 5: Role of frequency on photoelectric current.

List of Equations

  • Stopping potential, V0 is defined for circumstances when photoelectric current ceases.

  • Photon energy, E_p described as: Ep=h<br>uE_p = h <br>u; where h is Planck's constant and ν is the frequency.

  • Kinetic energy of photoelectrons defined by the equation: Ek=h<br>u−extφE_k = h <br>u - ext{φ}; where φ represents work function.