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
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
Current Electricity
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
Magnetic Effects of Current and Magnetism
Moving Charges and Magnetism
- Electromagnetism
- Magnetic force
- Motion in a Magnetic Field
- Magnetic Field Due to a Current Element, Biot-savart Law
- Magnetic Field on 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
Magnetism and Matter
Electromagnetic Waves
Optics
Electromagnetic Induction
Dual Nature of Radiation and Matter
Alternating Current
- AC Voltage Applied to a Resistor
- Representation of AC Current and Voltage by Rotating Vectors - Phasors
- AC Voltage Applied to an Inductor
- AC Voltage Applied to a Capacitor
- AC Voltage Applied to a Series LCR Circuit
- Phasor-diagram Solution
- Resonance
- Power in AC Circuit
- Transformers
- Overview: AC Circuits
Atoms and Nuclei
Electromagnetic Waves
- Concept of Electromagnetic Waves
- Displacement Current
- Sources of Electromagnetic Waves
- Nature of Electromagnetic Waves
- Electromagnetic Spectrum
- Overview of 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
- Overview of Ray Optics and Optical Instruments
Communication Systems
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
- Overview: Wave Optics
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
- Overview: Dual Nature of Radiation and Matter
Atoms
Nuclei
- Atomic Masses and Composition of Nucleus
- Size of the Nucleus
- Mass - Energy
- Nuclear Binding Energy
- Nuclear Force
- Radioactivity
- Forms of Energy > Nuclear Energy
- Nuclear Fission
- Nuclear Fusion
- Controlled Thermonuclear Fusion
- Overview: Nuclei
Semiconductor Electronics - Materials, Devices and Simple Circuits
- Concept of Semiconductor Electronics
- Classification of Metals, Conductors and Semiconductors
- Intrinsic Semiconductor
- Extrinsic Semiconductor
- n-type Semiconductor
- p-type Semiconductor
- Diode or p-n Junction
- Semiconductor Diode
- Application of Junction Diode as a Rectifier
- Overview: Semiconductor Electronics
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: 9 minutes
CBSE: Class 12
Introduction
An electric cell is a device that converts chemical energy into electrical energy. It consists of two electrodes (positive and negative terminals) immersed in an electrolyte (a conducting solution or paste). Chemical reactions within the electrolyte maintain a potential difference between the electrodes, which drives current through an external circuit.
CBSE: Class 12
Definition: EMF of a Cell
The emf of a cell is defined as the work done in carrying a unit positive charge through the complete circuit, including the charge flow inside the cell.
Unit: J/C (or) volt
CBSE: Class 12
Definition: Internal Resistance of a Cell
The resistance offered by the electrolyte of the cell when an electric current flows through it is known as internal resistance.
CBSE: Class 12
Definition: Terminal Potential Difference (V)
When current is drawn through a cell or current is supplied to it, then the potential difference across its terminals is called the terminal potential difference.
\[V=E-Ir\]
CBSE: Class 12
Derivation
Relation Between EMF, Terminal Voltage, and Internal Resistance
Setup: Consider a cell of EMF εε and internal resistance r, connected to an external resistance R. Let current I flow in the circuit.
Step 1: The cell drives current through both the external resistance R and its own internal resistance r.
Step 2: By Ohm's law, the potential drop across the internal resistance is:
Vinternal = Ir
Step 3: The remaining potential difference appears across the external resistance (terminal voltage):
V = ε − Ir ...(1)
Step 4: By Ohm's law applied to external resistance:
V = IR ...(2)
Step 5: From equations (1) and (2):
IR = ε − Ir
ε = I(R + r)
I = \[\frac {ε}{R+r}\] ...(3)
Step 6: Maximum current (when R = 0, i.e., short circuit):
Imax = \[\frac {ε}{r}\]
CBSE: Class 12
Discharging vs. Charging — Comparison Table
| Parameter | Discharging (Cell supplies current) | Charging (Current enters cell) | Open Circuit |
|---|---|---|---|
| Current direction | Out of (+) terminal | Into (+) terminal | No current |
| Terminal voltage formula | V = ε − Ir | V = ε + Ir | V = ε |
| Terminal voltage vs EMF | V < ε | V > ε | V = ε |
| Energy conversion | Chemical → Electrical | Electrical → Chemical | — |
CBSE: Class 12
Factors Affecting Internal Resistance
Internal resistance increases or decreases with the following factors:
| Factor | Effect on Internal Resistance |
|---|---|
| Distance between electrodes | Increases as distance increases |
| Surface area of electrodes | Decreases as the area increases |
| Nature of electrolyte | Depends on the ionic mobility of the solution |
| Concentration of electrolyte | Decreases with higher concentration |
| Temperature of the electrolyte | Decreases as temperature increases |
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