Dual Nature of Radiation & Matter: Physics

Introduction

• The lecture discusses the dual nature of radiation and matter.
• Focuses on modern physics.
• Relevant to board exams, JEE, and NEET.

Course Information and Structure

• This is the third-to-last lecture in the "विजेता सीरीज" (Victorious Series) for physics.
• The lecture is expected to last approximately 2.5 to 3 hours.
• The lecture includes detailed explanations, question practice, past year questions (PYQs), and a final revision.
• Students are advised to attend with concentration, keep a pen and register ready, and use earphones for better focus.

Telegram Channel

• Students are urged to join the Telegram channel "Triple S Army".
• The channel provides lecture notes and PYQ files.
• The file size is approximately 5.5 MB.
• Seek out the original Telegram channel for accurate information, as fake channels exist.

Electron Emission Methods

• Several methods can cause electron emission:
  • Thermionic Emission: Electrons are emitted due to heat.
  • Field Emission (Cold Cathode Emission): A strong electric field is applied.
  • Photoelectric Emission: Light causes electron emission.
  • Secondary Emission: Bombardment by other particles causes electron emission.

Work Function

• Work Function is the minimum energy required to emit an electron from an atom.
• Represented as h * ν₀, where ν₀ is the threshold frequency, and h is Planck's constant.
• Planck's constant is 6.6 x 10⁻³⁴ Joule seconds.
• Work Function is a property of individual materials (elements).

Photoelectric Emission

• Some metals are photo-sensitive and release electrons when exposed to sunlight.
• Not all photons cause electron emissions.
• Incoming photons give their energy to electrons.

Photoelectric Cell Setup

• Utilizes a photo-sensitive metal surface (the cathode), an anode (positive plate), and a cell connected in reverse polarity.

Role of Anode Potential

• The anode's positive potential attracts emitted electrons.
• Higher positive potential attracts more electrons, increasing current flow in the circuit.
• The plate can only attract electrons that have left the metal surface.
• Some electrons have enough energy to reach the anode without additional potential.

Electron Emission Based on Photon Energy

• If photon energy is less than the work function, no electron emission occurs.
• If photon energy equals the work function, electrons emit but have no kinetic energy.
• If photon energy is more than the work function, electrons emit with kinetic energy.

Material Properties and Emission

• Lower work function materials are preferred for photoelectric emission.
• If the energy of photons is greater than the Work function, the frequency of photons is more intense (hν > Work Function).
• If the energy of photons is greater than the Work function, the frequency of photons is more intense (ν > ν₀).

Photoelectric Phenomenon

• Photoelectric Emission occurs when electromagnetic radiation of sufficiently high frequency is incident on a metal.
• Ejected electrons are known as photo-generated electrons.

Photosensitive Materials

• Alkali metals (Lithium, Sodium, Potassium, Cesium, Rubidium) are highly photo-sensitive (emit electrons even with visible light).
• Metals like Zinc, Cadmium, Magnesium, and Aluminium respond only to ultraviolet light.
• Heavy metals respond only to X-rays.
• X-rays > UV radiation > Visible light (in terms of energy).

Intensity and Frequency

• Two main factors in the photoelectric effect:
  • Intensity (Number of Photons)
  • Frequency (Energy of Photons)

Intensity of Light

• The intensity of light is represented by the number of photons, specifically energy per area per time.

Effect of INTENSITY

• The number of electrons increases with intensity.
• Increased electron number increases current flow.

Potential Effect

• Photo Electric current VS Anode Potential relationship exists.
• Even when the Anode Potential is Zero, a small current continues to flow due to some electrons being ejected.
• After the anode increases, the flow of electrons continues.
• Electrons reach the anode and then the current becomes stable.

Cut Off-Potential

• Stops the flow of electrons.
• Will stop, reflect any and all electrons.
• Keeps the flow of electrons to virtually 0.

Saturation Current

• A point where the current increases and then remains constant.

Impact of Anode Potential

• Potential energy increases, creating greater kinetic energy.

Graph

• The "Cut-off" remains in a stationary location.
• Intensity increases during "Saturation."

Stopping Potential

• The negative potential at which the current is equal to ZERO.
• It is the minimum energy required to stop electrons from moving.

The Maximum Kinetic Energy is Used to Measure the Stopping Potential

• KE max = EVo
• The Kinetic Energy's measure will provide the stopping potential.

Equation

• E = Work + KEmax

Wave Length of the PhotoElectric Effects Graph

• "The Photons Frequency Effect"

Einstein's Theory

• Photon frequency (E = hv) is directly proportional to kinetic energy.
• Higher Frequency Shifts the graph further to the Left.
• Increasing Light intensity = Saturation Level Stays the Same

Threshold Freq

• The Threshold Frequency will always remain constant and retain the original saturation.

The "THRESHOLD" in Other Words

• Energy = MINIMUM energy to activate electrons.

Effect Of Freq

• Frequency is a material's property that directly transfers to Kinetic Energy.

Stopping VS Photo Energy

• Frequency increases.
• Frequency decreases.

Potential Stop

• Potential energy reduces due to "THE THRESHOLD" decreasing the potential.

IMPORTANT TAKEAWAY!

• PhotoElectric Currents increase when Intensity increases.
• Potential Energy Increases if Frequency Increases.

GRAPH

• The graph will always shift further left if Frequency energy is increasing.

Laws of PhotoElectric Emission

• For a given photosensitive material and frequency with THRESHOLD is greater or above, the energy will eject the particle (ν > ν₀).

"Current" Relationship

• PhotoElectric Is directly proportional to light intensity

Existential THRESHOLDS

• THRESHOLD frequency exists, below which Photo's are NEVER ejected.

THRESHOLD Details.

• Stopping Potential / KE max = Directly Proportional to Energy

The Rate

• With energy being greater than the work function are CAPABLE OF EJECTING ENERGY.

Lecture on the dual nature of radiation and matter, focusing on modern physics for board exams, JEE, and NEET. Includes explanations, question practice, past year questions (PYQs), and a final revision. Join the Telegram channel 'Triple S Army' for lecture notes and PYQ files.