Topics
Electric Charges and Fields
- Electric Charge
- Conductors and Insulators
- Basic 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
Electromagnetic Induction and Alternating Currents
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 Waves
Magnetism and Matter
Electromagnetic Induction
Optics
Dual Nature of Radiation and Matter
Alternating Current
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
- Optical Instruments
- Microscope and it’s types
- Telescope
Wave Optics
- Concept of 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
The Special Theory of Relativity
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
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.
