Current Electricity
Class 12 · Current Electricity
Internal Resistance & V_terminal
V = ε − Ir. As R drops, more voltage is wasted across r.
Key Notes
01
Real cell: emf ε, internal resistance r. Terminal voltage V = ε − Ir.
02
Power delivered to load = ε²R/(R+r)². Maximum when R = r (matched load).
03
When I = 0 (open circuit), V = ε.
Formulas
Terminal voltage
Drops as I increases.
Max power transfer
P_max = ε²/(4r).
Important Points
Old/dead batteries have higher internal resistance.
Short-circuit current = ε/r — limits current even with R_load = 0.
Internal Resistance & V_terminal notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 12 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.