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Physics · Class 12 · Current Electricity

Current Electricity for JEE

Everything you need for this topic on one page: the ideas, the formulas, the traps, and free lectures that explain it well.

Last updated: 26 October 2026

Direct answer

Ohm's law, resistivity, Kirchhoff's laws, cells, Wheatstone bridge, metre bridge, potentiometer and power in circuits.

Ohm's law, resistivity, Kirchhoff's laws, cells, Wheatstone bridge, metre bridge, potentiometer and power in circuits.

Key ideas

Current Electricity: what you must understand

  • Drift velocity v_d = I/(neA)
  • Kirchhoff's junction rule (charge) and loop rule (energy)
  • Balanced Wheatstone bridge: P/Q = R/S
  • Terminal voltage V = E − Ir when supplying current
Formula sheet

Must-know formulas for Current Electricity

  • R = ρL/A
  • Series: R = ΣRᵢ; parallel: 1/R = Σ1/Rᵢ
  • Power P = VI = I²R = V²/R
  • Max power transfer when external R = internal r
Print

One-page formula sheet

Printable Current Electricity formula sheet: formulas, key ideas and traps on one page. Save it as a PDF for offline revision.

Avoid

Common mistakes students make

  • Sign errors in the loop rule
  • Missing a balanced bridge that removes a resistor
  • Forgetting resistance changes when a wire is stretched (R ∝ L²)
For the exam

How this topic is asked in JEE

Appears in almost every JEE Main shift. High frequency. Practise reducing circuits by symmetry and spotting balanced bridges.

NCERT map

Where Current Electricity is in NCERT

Chapter names follow the current rationalised NCERT textbooks. Read these sections before solving PYQs.

ClassBookChapterSections JEE asks from
Class 12Physics Part ICurrent ElectricityOhm's Law; Drift of Electrons and the Origin of Resistivity; Cells, EMF, Internal Resistance; Kirchhoff's Rules; Wheatstone Bridge; Potentiometer
JEE Advanced level

A JEE Advanced-level example on Current Electricity

Question. A potentiometer wire AB of length 100 cm and total resistance 5 Ω is connected to a driver cell of EMF 4 V and internal resistance 1 Ω. An unknown cell of EMF E with internal resistance r gives a balance length of 40 cm in open circuit. When a 4 Ω resistance is connected across this cell, the balance length becomes 32 cm. Find the internal resistance r of the unknown cell.

Show solution
  1. Current in main circuit: I = 4/(5 + 1) = 2/3 A. Potential gradient k = (I × 5)/100 = (2/3 × 5)/100 = 1/30 V/cm
  2. Open circuit balance: E = k × 40 = (1/30) × 40 = 4/3 V
  3. With 4 Ω connected, current through cell: i = E/(r + 4). Terminal voltage V = E − ir = E × 4/(r + 4)
  4. New balance: V = k × 32 = 16/15 V
  5. So (4/3) × 4/(r + 4) = 16/15. Solving: 16/[3(r + 4)] = 16/15, giving 3(r + 4) = 15, so r + 4 = 5

Answer: r = 1 Ω

This example was solved twice independently and both solutions agree.

Free lectures

Best free lectures for Current Electricity

Full-chapter free lectures picked from YouTube search results by views, from established JEE channels (mostly in Hinglish). Use the subtopic list to jump straight to the part you need (timestamps come from each video's own chapter list). Watch one, then solve PYQs the same day.

Practise

Where to practise for free

FAQs

Frequently asked questions

Is Current Electricity important for JEE Main 2027?

Appears in almost every JEE Main shift. It is part of the official 'Current Electricity' unit in the JEE Main 2027 syllabus.

What are the most important formulas in Current Electricity?

R = ρL/A; Series: R = ΣRᵢ; parallel: 1/R = Σ1/Rᵢ; Power P = VI = I²R = V²/R.

How should I study Current Electricity for JEE?

Understand the key ideas from NCERT or one full lecture, learn the formula sheet, then solve 25–30 past JEE questions on the topic. High frequency. Practise reducing circuits by symmetry and spotting balanced bridges.

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