Current Electricity — Class 12 CBSE Physics revision notes
A 7-page visual revision sheet for Current Electricity, written for Class 12 CBSE Physics. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.
Page 1 as PDF
Current Electricity in one look
charge on the move, and what stands in its way
Current, and current in conductors
- current I = Q/t, the rate of charge crossing a cross-section, unit ampere
- conventional current runs the way a positive charge would move, opposite to electron flow in metals
- conductors: free electrons carry the current; electrolytes: both + and − ions carry it, adding
- current is a scalar: currents add arithmetically at a junction, never by a vector rule
Ohm's law
- Ohm's law, physical conditions unchanged
V = IR - resistance from geometry
R = ρ L/A - conductance
G = 1/R - conductivity
σ = 1/ρ - current density form
j = σ E
Ohmic vs non-ohmic
- V-I is a straight line through the origin
- metals, resistors, wires at fixed temperature
- V-I bends, or is not single valued
- diode, gas discharge tube, a heated filament
Page 1 of 7. The full sheet, all 7 pages, opens free in the app.
What this Current Electricity sheet covers
- Current, and current in conductors
- Ohm's law
- Ohm's law, physical conditions unchanged
- resistance from geometry
- conductance
- conductivity
- current density form
- Ohmic vs non-ohmic
- Ohmic
- Non-ohmic
- Drift velocity and mobility
- Where Ohm's law fails
- Resistivity: conductors, semiconductors, insulators
- Resistivity and temperature
- metals: resistivity rises with temperature
- temperature coefficient of resistivity
- Electrical power
- power delivered
- current fixed, R known
- voltage fixed, R known
- energy in time t
- Power transmission
- Emf and internal resistance
- discharging, through an external R
- charging, against the emf
- internal resistance
- current in a simple circuit
- Limits of emf and terminal voltage
- Cells in series and parallel
- n cells in series
- n identical cells in parallel
- mixed grouping, m rows of n cells, current peaks when
- Kirchhoff's rules
- The Wheatstone bridge
- In the lab: resistivity by a V-I graph
- Combination of Resistors
- series and parallel resistors
- In the lab: the metre bridge
- Activity: potential drop along a wire
- Symbols
- Charging and discharging a capacitor
- Endless ladders and symmetric networks
- Traps that cost marks
- Tricks that save time
How CapCompass uses this sheet
These notes are not a standalone PDF. CapCompass plans Physics chapter by chapter against your real exam dates and free hours, and when the plan reaches Current Electricity the sheet opens inside the study block itself — at the page covering the sub-topic that block is on, with the timer still running. Revision arrives at the moment the plan says revise, instead of having to be gone looking for.