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Current Electricity Fundamentals and Principles
May 19, 2024
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Review flashcards
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Mindmap
Current Electricity (Class 12 Physics Chapter 3)
Introduction
Objective: Comprehensive coverage of current electricity - numericals, derivations, concepts, graphs
Feature: Aid in understanding, solve previous year questions
New Series: NCERT Reading Series
Information: Difficulty in reading NCERT, line-by-line coverage
Basics of Current Electricity
Previous Chapter: Electrostatics
Current Electricity: Moving charge
Electric Current: Flow of charge, current = stream
Current Intensity: Strength of current, I = Q/t, Unit: Ampere
Charge Carriers in Different Things
Metals: Free electrons
Electrolytes: Ions (positive, negative)
Gases: Free electrons and ions
Quantity of Current
Current: Scalar quantity (only magnitude, no impact of direction)
Direction: From negative to positive (real direction), from positive to negative (conventional direction)
Current Numericals
Turbulent format, calculation important
Current Density
Definition: Current per unit area
Formula: J = I/A
Unit: A/m┬▓
Vector quantity
Drift Velocity
Random motion does not lead to current flow
Electron drifts when potential difference is applied
Charge Carrier: Free electrons
Formula: vd = I / neA (given velocity)
Relaxation Time
Time between the first and second collision
Relaxation time decreases with increasing temperature
Relationship Between Electric Current Intensity and Drift Velocity
I = neAvd
Current Density J = n e vd
Discovery Velocity
Drift Velocity vs Thermal Velocity
th = ~10-4 m/s, thermal = 10^5 m/s
Ohm's Law
Electric current is directly proportional to the potential across + resistance (V = IR)
Resistance: Obstruction to charge flow
Resistivity: Resistance per unit volume (╧Б = R * A / L)
Resistance Unit: Ohm, Conductance: Siemens (S)
Dependence on Calibration
Increasing length compromises conductance (L тИЭ R)
Cutting the cross-sectional area increases conductance and density (A тИЭ 1/R)
Resistance and resistivity: Material and temperature dependent
R = ╧Б(L/A)
Equalizing Electrodes
Main: Error set by angle A is assessed
Positive resistance: Increasing slope
Negative resistance: Decreasing slope
Wheatstone Bridge Principle
Measurement of unknown resistance
P/Q = R/S
No current in galvanometer when current flows: Balance condition
Electric Power and Energy
Power: Rate of doing work (P = VI)
Energy: E = Pt
Power Unit = Watt, Energy Unit = Joule
Power Rating
Rating provided by the manufacturer: Rated power
Power Unit: Kilowatt-hour (kWh)
Importance of rating, description of each unit
Kirchhoff's Laws
Two laws: KirchhoffтАЩs current law (junction rule), KirchhoffтАЩs voltage law (loop rule)
Junction rule: The current that comes into a junction is equal to the current that leaves (current reaching = current leaving)
Voltage rule: The sum of potential differences in a closed loop is always zero
Numericals
Practice on examples of power, energy
Electromotive Force (EMF)
Not a force, but energy
Source of a battery or cell
EMF = V + Ir
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