Home
Learn
Plan & Focus
Community
Pricing
Play & Compete
Free Resources

Log in Join Free

by JEE Master

Ask. Share. Learn. Grow Together. India's all-in-one community for JEE Main & JEE Advanced aspirants.

Explore

Learn
Plan & Focus
Community
Play & Compete
Free Resources

Resources

JEE Main PYQs
JEE Advanced PYQs
Formula Sheets
NCERT Mapping
Mock Analysis

Support

Help Center
Privacy Policy
Terms of Use
Contact Us

© 2026 PadhoNa. All rights reserved.

Formula Sheets / Physics

Chapter 20

Current Electricity

Revise with flashcards Download this chapter (PDF) All Physics formulas (PDF)

Current, drift velocity and Ohm's law Combinations and Kirchhoff's laws Cells, EMF and internal resistance Heating effect and power Meter bridge, potentiometer and instruments

Current, drift velocity and Ohm's law

$R = \frac{ρ L}{A}$ $V = I R,$ $R = \frac{ρ L}{A}$
$J = σ E,$ $ρ = \frac{m}{n e ^{2} τ},$ $μ = \frac{v _{d}}{E}$
Temperature
$R = R_{0} (1 + α Δ T)$
Stretched wire
length $\times n \Rightarrow R \times n^{2}$ (same volume)

Combinations and Kirchhoff's laws

series $R = R_{1} + R_{2};$ parallel $\frac{1}{R} = \frac{1}{R _{1}} + \frac{1}{R _{2}}$
Kirchhoff
$\sum I = 0$ (junction) $;$ $\sum Δ V = 0$ (loop)
Wheatstone bridge balanced
$\frac{P}{Q} = \frac{R}{S}$

Cells, EMF and internal resistance

$V = ε - I r,$ $I = \frac{ε}{R + r}$
Cells in series / parallel
$ε_{eq} = \sum ε_{i}, r_{eq} = \sum r_{i};$ $ε_{eq} = \frac{\sum ε _{i} / r _{i}}{\sum 1/ r _{i}}, \frac{1}{r _{eq}} = \sum \frac{1}{r _{i}}$
Maximum power
$R = r : P_{m a x} = \frac{ε ^{2}}{4 r}$

Heating effect and power

$P = V I = I^{2} R = \frac{V ^{2}}{R},$ $H = I^{2} R t$

Meter bridge, potentiometer and instruments

Meter bridge
$\frac{R}{S} = \frac{l}{100 - l}$
Potentiometer
$\frac{ε _{1}}{ε _{2}} = \frac{l _{1}}{l _{2}};$ $r = R (\frac{l _{1}}{l _{2}} - 1)$
Galvanometer conversions
ammeter: $S = \frac{I _{g} G}{I - I _{g}}$ (shunt) $;$ voltmeter: $R = \frac{V}{I _{g}} - G$ (series)

Capacitance Magnetic Effects of Current