Topics
Electric Charges and Fields
- Electric Charges
- Conductors and Insulators
- Properties of Electric Charge
- Coulomb’s Law
- Forces between Multiple Charges
- Electric Field
- Electric Field Due to a System of Charges
- Physical Significance of Electric Field
- Electric Field Lines
- Electric Flux
- Electric Dipole
- Dipole in a Uniform External Field
- Continuous Charge Distribution
- Gauss’s Law
- Application of Gauss' Law
Electrostatics
Current Electricity
Electrostatic Potential and Capacitance
- Electric Potential and Potential Energy
- Electrostatic Potential
- Electric Potential Due to a Point Charge
- Potential Due to an Electric Dipole
- Potential due to a System of Charges
- Equipotential Surfaces
- Relation Between Electric Field and Electrostatic Potential
- Potential Energy of a System of Charges
- Potential Energy of a Single Charge
- Potential Energy of a System of Two Charges in an External Field
- Potential Energy of a Dipole in an External Field
- Electrostatics of Conductors
- Dielectrics and Polarisation
- Capacitors and Capacitance
- The Parallel Plate Capacitor
- Effect of Dielectric on Capacitance
- Combination of Capacitors
- Energy Stored in a Charged Capacitor
Magnetic Effects of Current and Magnetism
Current Electricity
- Electric Current
- Electric Currents in Conductors
- Ohm's Law
- Drift of Electrons and the Origin of Resistivity
- Mobility of Electrons
- Limitations of Ohm’s Law
- Resistivity of Various Materials
- Temperature Dependence of Resistivity
- Electrical Energy and Power in Conductors
- Cells, EMF, and Internal Resistance
- Cells in Series and in Parallel
- Kirchhoff’s Laws
- Wheatstone Bridge
Moving Charges and Magnetism
- Electromagnetism
- Magnetic force
- Motion in a Magnetic Field
- Magnetic Field Due to a Current-carrying Conductor: Biot-savart's Law
- Applications of Biot-Savart's Law > Magnetic Field at the Axis of a Circular Current-carrying Loop
- Ampere’s Circuital Law
- Solenoid
- Force Between Two Parallel Currents (Ampere’s Law)
- Torque on a Rectangular Current Loop in a Uniform Magnetic Field
- Circular Current Loop as a Magnetic Dipole
- Moving Coil Galvanometer
- Kirchhoff’s Laws
Electromagnetic Induction and Alternating Currents
Electromagnetic Waves
Magnetism and Matter
Optics
Electromagnetic Induction
Alternating Current
Dual Nature of Radiation and Matter
Atoms and Nuclei
Electromagnetic Waves
Electronic Devices
Ray Optics and Optical Instruments
- Ray Optics Or Geometrical Optics
- Reflection of Light by Spherical Mirrors
- Sign Convention for Reflection by Spherical Mirrors
- Focal Length of Spherical Mirrors
- Mirror Equation of Spherical Mirrors
- Refraction of Light
- Total Internal Reflection
- Applications of Total Internal Reflection
- Refraction at a Spherical Surfaces
- Refraction by a Lens
- Power of a Lens
- Combined Focal Length of Two Thin Lenses in Contact
- Refraction of Light through a Prism
- Introduction to Optical Instruments
- Microscope and it’s types
- Telescope
Wave Optics
- Introduction to Wave Optics
- Huygens Principle
- Refraction of a Plane Wave
- Refraction at a Rarer Medium
- Reflection of a Plane Wave by a Plane Surface
- Coherent and Incoherent Addition of Waves
- Interference of Light Waves and Young’s Experiment
- Diffraction of Light
- The Single Slit
- Seeing the Single Slit Diffraction Pattern
- Polarisation of Light
Communication Systems
Dual Nature of Radiation and Matter
- Understanding Dual Nature of Radiation and Matter
- Electron Emission
- Photoelectric Effect - Hertz’s Observations
- Photoelectric Effect - Hallwachs’ and Lenard’s Observations
- Experimental Study of Photoelectric Effect
- Effects of Intensity and Frequency on Photocurrent
- Photoelectric Effect and Wave Theory of Light
- Einstein’s Photoelectric Equation: Energy Quantum of Radiation
- Particle Nature of Light: The Photon
- Wave Nature of Matter
The Special Theory of Relativity
Atoms
Nuclei
Semiconductor Electronics - Materials, Devices and Simple Circuits
Communication Systems
- Detection of Amplitude Modulated Wave
- Production of Amplitude Modulated Wave
- Basic Terminology Used in Electronic Communication Systems
- Sinusoidal Waves
- Modulation and Its Necessity
- Amplitude Modulation (AM)
- Need for Modulation and Demodulation
- Satellite Communication
- Propagation of EM Waves
- Bandwidth of Transmission Medium
- Bandwidth of Signals
The Special Theory of Relativity
- The Special Theory of Relativity
- The Principle of Relativity
- Maxwell'S Laws
- Kinematical Consequences
- Dynamics at Large Velocity
- Energy and Momentum
- The Ultimate Speed
- Twin Paradox
Estimated time: 8 minutes
CBSE: Class 12
Aim of the Experiment
- To study the emission of electrons from a metal surface when light falls on it.
- To examine how photocurrent varies with applied potential, light intensity, and incident radiation frequency.
- To identify important observations that cannot be explained completely by the classical wave theory of light.
CBSE: Class 12
Experimental Arrangement
Apparatus Used:
- Evacuated glass/quartz tube.
- Photosensitive metal plate C (emitter).
- Collector plate A.
- Quartz window W for incident radiation.
- Monochromatic light source S.
- A battery for applying a potential difference.
- A voltmeter is used to measure the potential difference.
- Microammeter to measure photocurrent.
- Commutator or reversing arrangement to change polarity between plates.
Function of Main Parts
| Part | Function |
|---|---|
| Emitter plate C | Emits electrons when light falls on it. |
| Collector plate A | Collects emitted electrons and helps measure current. |
| Quartz window W | Allows suitable radiation, especially ultraviolet, to enter the tube. |
| Battery | Creates accelerating or retarding potential between plates. |
| Microammeter | Detects the small current produced by photoelectrons. |
CBSE: Class 12
Procedure
- Keep the emitter plate C illuminated by monochromatic radiation.
- Apply a potential difference between the emitter and the collector.
- Measure the resulting photocurrent using the microammeter.
- Change the collector potential and observe how current varies.
- Reverse the polarity to study the stopping of photoelectrons.
- Change light intensity and note the change in photocurrent.
- Change the light frequency using suitable filters and study the effect on emission and electron energy.
CBSE: Class 12
Main Observations
A. Effect of collector potential
- When the collector is made positive with respect to the emitter, more emitted electrons are attracted to it, increasing the photocurrent.
- At a sufficiently high positive potential, all emitted electrons are collected, and the current reaches its maximum; this is the saturation region.
- When the collector is made negative, it repels electrons and photocurrent decreases.
- At a certain negative potential, photocurrent becomes zero; this potential is the stopping potential.
B. Effect of the intensity of light
- For frequencies above the threshold, the photocurrent increases with increasing incident light intensity.
- Greater intensity means more photons per second reaching the metal surface, so more electrons are emitted.
- Stopping potential does not increase just because intensity increases.
C. Effect of frequency of light
- If the frequency of incident radiation is below the threshold frequency, no photoelectric emission occurs, however strong the light may be.
- For frequencies above the threshold, photoelectrons are emitted.
- As frequency increases, the maximum kinetic energy of emitted electrons increases, so the stopping potential increases.
D. Time lag of emission
- Photoelectric emission is essentially instantaneous when suitable radiation falls on the metal surface.
- This observation was one of the major difficulties for classical wave theory.
