Electrostatic Potential and Capacitance — Class 12 CBSE Physics revision notes
A 6-page visual revision sheet for Electrostatic Potential and Capacitance, 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
Electrostatic Potential and Capacitance in one look
potential is a number, capacitance is geometry
Electrostatic potential
- work done by an external force bringing q from infinity to P, without accelerating it
- V_P = W/q: work per unit charge, unit volt = J/C
- the field is conservative: the work depends only on the ends, not the path
- only differences have meaning: V_P - V_R = W_RP/q, V = 0 at infinity by choice
Potential due to a point charge
- V = 1/4πε_0q/r, falls as 1/r, gentler than E's 1/r^2
- +q: V positive all round it. -q: V negative, deepest near it
- the same at every point of a sphere round q
Potential due to a dipole
- V = 1/4πε_0pcosθ/r^2, for r >> a
- axis: V = ±1/4πε_0p/r^2. equator: V = 0 everywhere
- falls as 1/r^2, faster than a point charge; depends on the angle too
Potential due to a system of charges
- V = 1/4πε_0Σ q_i/r_i: a plain sum with signs, no components
- charged shell, outside: as if all of q sat at the centre
- inside the shell: V = q/4πε_0R everywhere, constant, so E = 0
Page 1 of 6. The full sheet, all 6 pages, opens free in the app.
What this Electrostatic Potential and Capacitance sheet covers
- Electrostatic potential
- Potential due to a point charge
- Potential due to a dipole
- Potential due to a system of charges
- Equipotential surfaces
- Field from potential
- E is minus the potential gradient
- in a uniform field, across a gap d
- Where the minus sign comes from
- Potential energy of a system of charges
- Self energy of a charged sphere
- conducting shell, charge Q radius R
- uniformly charged solid sphere
- Potential energy in an external field
- Electrostatics of conductors
- Dielectrics and polarisation
- Capacitors and capacitance
- definition
- parallel plate, vacuum
- gap filled with dielectric K
- unit, farad
- Sphere and cylinder capacitors
- isolated sphere, radius R
- spherical, inner a outer b
- cylindrical, length L
- Sliding in a dielectric
- Battery still connected
- Battery disconnected
- A slab only part-way in
- dielectric slab of thickness t
- metal slab of thickness t (K → ∞)
- Series vs parallel
- Series
- Parallel
- Limits worth checking
- Energy stored in a capacitor
- work done charging it
- energy density in the field
- force between the plates
- Two capacitors sharing charge
- joined plus to plus, common V
- energy lost as heat and spark
- Symbols
- 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 Electrostatic Potential and Capacitance 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.