How much of JEE Main comes from Current Electricity?

JEEGenie estimates about 6% of JEE Main marks come from Current Electricity, based on recent papers. The share varies from year to year.

Which formulas matter most in Current Electricity?

The Current Electricity sheet on this page has 24 formula entries, starting with Electric Current, Current Density, Drift Velocity, Ohm's Law, Resistivity and Conductivity. Each one comes with when to use it and the trap to avoid.

What topics does Current Electricity cover for JEE?

Current Electricity covers Ohm's Law and Resistance, Kirchhoff's Laws, Wheatstone Bridge, Cells and EMF, Electrical Power, Potentiometer and Meter Bridge.

How should I revise Current Electricity before the exam?

Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens Current Electricity questions on JEEGenie.

How many previous-year questions are there on Current Electricity?

JEEGenie has 518 previous-year questions on Current Electricity, and this page shows a few with worked explanations.

Is practice on Current Electricity free on JEEGenie?

Sign-up is free and includes a 7-day Pro trial. After the trial, free accounts keep a limited daily quota.

Current Electricity for JEE Main & Advanced — formulas, what is asked, and traps

JEEGenie estimates about 6% of JEE Main marks come from Current Electricity. This page covers 24 formula entries, each with when to use it, what JEE asks and the traps. A common slip: Do not treat current as a vector; it is a scalar with a defined direction.

Key points to know

Electric Current. Electric current is the net flow of charge per unit time through a cross-section. It is a scalar quantity, but its direction is taken as the direction of flow of positive charge.
Current Density. Current density is the current per unit area, a vector quantity pointing in the direction of current flow. It relates microscopic and macroscopic current.
Drift Velocity. Drift velocity is the average velocity of charge carriers in a conductor due to an electric field. It is very small (mm/s) but produces large current due to high number density.
Ohm's Law. Ohm's law states that the current through a conductor is directly proportional to the potential difference across it, provided physical conditions (temperature, etc.) remain constant.
Resistivity and Conductivity. Resistivity ( $ρ$ ) is a material property that quantifies how strongly it opposes current. Conductivity ( $σ$ ) is its reciprocal. Both depend on temperature and material.
Electromotive Force (EMF) and Internal Resistance. EMF is the potential difference across a battery when no current flows. Internal resistance ( $r$ ) causes terminal voltage to drop when current flows.
Electrical Energy and Joule Heating. When current flows through a resistor, electrical energy is converted to heat. This is Joule heating, used in heaters and bulbs.

Formula sheet

Name	Formula	When to use
Electric Current	$I = \frac{d q}{d t}$	Use when calculating current from charge flow or vice versa, especially in steady-state circuits.
Current Density	$\vec{J} = \frac{I}{A} \hat{n}$	Use when dealing with microscopic properties like drift velocity or when current distribution is non-uniform.
Drift Velocity	$v_{d} = \frac{I}{n e A} = \frac{e E τ}{m}$	Use to relate current to microscopic parameters like number density, charge, and relaxation time.
Ohm's Law	$V = I R$	Use for simple resistive circuits to find voltage, current, or resistance.
Resistivity and Conductivity	$R = ρ \frac{L}{A}$ , $σ = \frac{1}{ρ} = \frac{n e^{2} τ}{m}$	Use to calculate resistance from material properties or to compare conductors of different materials.
Temperature Dependence of Resistance	$R_{T} = R_{0} (1 + α Δ T)$	Use when temperature changes affect circuit behavior, e.g., in heating elements or thermistors.
Series and Parallel Combinations	$R_{s} = R_{1} + R_{2} + \dots$ , $\frac{1}{R_{p}} = \frac{1}{R_{1}} + \frac{1}{R_{2}} + \dots$	Use to simplify complex resistor networks into a single equivalent resistance.
Kirchhoff's Laws	$\sum I_{i n} = \sum I_{o u t}$ , $\sum V = 0$	Use for any circuit that cannot be simplified by series/parallel alone (e.g., multi-loop circuits).
Electromotive Force (EMF) and Internal Resistance	$V = E - I r$	Use when analyzing real batteries in circuits, especially when current is drawn.
Wheatstone Bridge	$\frac{R_{1}}{R_{2}} = \frac{R_{3}}{R_{4}}$	Use to measure unknown resistance accurately by comparing with known resistances.
Meter Bridge	$\frac{R}{S} = \frac{l}{100 - l}$	Use in practical problems to find unknown resistance or to compare two resistances.
Potentiometer	$E = k l$ , where $k = \frac{V}{L}$ (potential gradient)	Use to compare EMFs of cells or to measure internal resistance of a cell.
Power in Electrical Circuits	$P = I^{2} R = \frac{V^{2}}{R} = V I$	Use to calculate heat dissipation, energy consumption, or efficiency of circuits.
Maximum Power Transfer Theorem	$P_{m a x} = \frac{E^{2}}{4 r}$ when $R_{L} = r$	Use when designing circuits to maximize power to a load (e.g., speaker impedance matching).
Electrical Energy and Joule Heating	$H = I^{2} R t = \frac{V^{2}}{R} t = V I t$	Use to calculate heat generated in resistors, fuses, or heating elements.
Color Code for Resistors	$R = (10 \times d_{1} + d_{2}) \times 10^{m} \pm tolerance$	Use to decode resistor values in practical circuits or exam problems.
Ammeter and Voltmeter	Ammeter: $I_{g} R_{g} = (I - I_{g}) S$ ; Voltmeter: $V = I_{g} (R_{g} + R_{s})$	Use when designing or analyzing measurement instruments in circuits.
Galvanometer Conversion	Ammeter: $S = \frac{I_{g} R_{g}}{I - I_{g}}$ ; Voltmeter: $R_{s} = \frac{V}{I_{g}} - R_{g}$	Use to solve problems involving galvanometer conversion to extend measurement range.
Delta-Star Transformation	$R_{a} = \frac{R_{a b} R_{a c}}{R_{a b} + R_{b c} + R_{c a}}$ , etc.	Use to simplify complex resistor networks like bridge circuits or three-phase connections.
Symmetry in Circuits	No single formula; use symmetry to reduce complexity.	Use for complex networks like cubes, infinite grids, or balanced bridges.
Infinite Ladder Network	$R_{e q} = R + \frac{R \cdot R_{e q}}{R + R_{e q}}$ (for simple ladder)	Use when dealing with infinite repeating resistor networks.
Cell Grouping	Series: $E_{e q} = n E$ , $r_{e q} = n r$ ; Parallel: $E_{e q} = E$ , $r_{e q} = r / m$	Use to design battery packs for desired voltage and current.
Kirchhoff's Laws with Multiple Batteries	No single formula; use $\sum I R = \sum E$ around a loop.	Use for any circuit with multiple batteries and resistors that cannot be simplified.
Superposition Theorem	No single formula; apply one source at a time.	Use when a circuit has multiple sources and you want to find current in a particular branch.

Open the Current Electricity formula page

What JEE asks

Electric Current. JEE often asks to find current given charge as a function of time, e.g., $q = t^{2} + 2 t$ , then differentiate.
Current Density. JEE may ask to find drift velocity given current density and number density of charge carriers.
Drift Velocity. JEE often asks to compare drift velocities in different wires (series/parallel) or find $v_{d}$ given current and cross-section.
Ohm's Law. JEE often tests by giving V-I graphs and asking which is ohmic or finding resistance from slope.
Resistivity and Conductivity. JEE often asks to find resistance after stretching a wire (volume constant) or temperature coefficient problems.
Temperature Dependence of Resistance. JEE may ask to find resistance at a given temperature or compare resistances of two materials with different $α$ .
Series and Parallel Combinations. JEE often gives complex networks (like cube, infinite ladder) and asks for equivalent resistance.
Kirchhoff's Laws. JEE often asks to find currents in each branch of a circuit with multiple batteries and resistors.
Electromotive Force (EMF) and Internal Resistance. JEE often asks to find internal resistance from open-circuit and load voltage, or maximum power transfer.
Wheatstone Bridge. JEE often asks to find unknown resistance in a balanced bridge or to find error in measurement.
Meter Bridge. JEE may ask to find unknown resistance given balance length, or to find error due to end corrections.
Potentiometer. JEE often asks to find EMF ratio from balance lengths, or internal resistance using potentiometer.
Power in Electrical Circuits. JEE often asks to find power in different resistors in a circuit, or to find condition for maximum power.
Maximum Power Transfer Theorem. JEE may ask to find load resistance for maximum power or the value of maximum power.
Electrical Energy and Joule Heating. JEE often asks to compare heat produced in series vs parallel combinations of resistors.
Color Code for Resistors. JEE may ask to find resistance value from color bands or vice versa.
Ammeter and Voltmeter. JEE often asks to find shunt resistance to convert a galvanometer into an ammeter or voltmeter.
Galvanometer Conversion. JEE often asks to calculate shunt or series resistance for a given range.
Delta-Star Transformation. JEE often asks to find equivalent resistance of a network using delta-star conversion.
Symmetry in Circuits. JEE often asks to find equivalent resistance of a cube or infinite ladder using symmetry.
Infinite Ladder Network. JEE often asks to find equivalent resistance of an infinite ladder of resistors.
Cell Grouping. JEE may ask to find current in external resistance for a given grouping of cells.
Kirchhoff's Laws with Multiple Batteries. JEE often gives a circuit with two or three loops and asks to find currents or potential differences.
Superposition Theorem. JEE may ask to find current in a resistor using superposition in a circuit with two batteries.

Common traps

Do not treat current as a vector; it is a scalar with a defined direction. Electric Current
Current density is a vector, not a scalar; its direction is the direction of electric field in isotropic conductors. Current Density
Drift velocity is not the speed of individual electrons; it is an average velocity. Drift Velocity
Ohm's law is not a universal law; it applies only to ohmic conductors (metals at constant temperature). Ohm's Law
Resistivity is independent of the geometry of the conductor; resistance depends on length and area. Resistivity and Conductivity
The formula is approximate and valid only for small temperature changes. Temperature Dependence of Resistance
For parallel, the equivalent resistance is always less than the smallest individual resistance. Series and Parallel Combinations
Assign current directions arbitrarily; if answer is negative, direction is opposite. Kirchhoff's Laws
EMF is not a force; it is a potential difference (unit: volt). Electromotive Force (EMF) and Internal Resistance
The bridge is balanced only when galvanometer shows zero deflection; do not assume it is balanced otherwise. Wheatstone Bridge
The wire is uniform, so resistance is proportional to length. Meter Bridge
Potentiometer measures EMF accurately because it draws no current at balance. Potentiometer
Use $P = I^{2} R$ when current is constant (series), $P = V^{2} / R$ when voltage is constant (parallel). Power in Electrical Circuits
This theorem applies only to DC circuits with linear sources. Maximum Power Transfer Theorem

Topics in Current Electricity

Ohm's Law and Resistance
Kirchhoff's Laws
Wheatstone Bridge
Cells and EMF
Electrical Power
Potentiometer and Meter Bridge

Previous-year questions on Current Electricity

JEEGenie has 518 previous-year questions on Current Electricity. A few worked examples follow.

Year	Questions
2026	28
2025	19
2024	48
2023	49
2022	52
2021	56
2020	24
2019	76
2018	12
2017	12
2016	10
2015	13
2014	9
2013	13
2012	5
2011	3
2010	6
2009	1
2008	5
2007	2
2006	8
2005	12
2004	12
2003	11
2002	8
1999	1
1997	2
1995	1
1993	1
1991	1
1989	1
1988	2
1987	2
1985	1
1984	1
1983	1
1982	3
1981	1
1980	1
1979	2
1978	3

Question 1 medium

Two resistors of 200

Ω

and 400

Ω

are connected in series with a battery of 100 V. A bulb rated at 200 V, 100 W is connected across the 400

Ω

resistance. The potential drop across the bulb is ________ V.

25
50
66.6
100

Answer: B

Explanation. The bulb's resistance is

R_{b} = \frac{V^{2}}{P} = \frac{200^{2}}{100} = 400 Ω .

The bulb is in parallel with the

400 Ω

resistor, so their equivalent resistance is

R_{p} = \frac{400 \times 400}{400 + 400} = 200 Ω .

This parallel combination is in series with the

200 Ω

resistor, giving total resistance

R_{total} = 200 + 200 = 400 Ω .

The current from the 100 V battery is

I = \frac{100}{400} = 0.25 A .

The potential drop across the parallel combination (and hence across the bulb) is

V_{bulb} = I R_{p} = 0.25 \times 200 = 50 V .

50 V

**Answer: B**

From NTA/IIT papers: JEE Main 2026 · 2 Apr Shift 2

Question 2 easy

The battery of a mobile phone is rated as

4.2 V, 5800 m A h

. How much energy is stored ir it when fully charged?

87.7 kJ
43.8 kJ
48.7 kJ
24.4 kJ

Answer: A

Explanation. The battery rating gives voltage

V = 4.2 V

and charge capacity

Q = 5800 m A h

. Convert charge to coulombs:

5800 m A h = 5800 \times 10^{- 3} \times 3600 C = 20880 C

. Energy stored:

E = V \cdot Q = 4.2 \times 20880 = 87696 J \approx 87.7 k J

. Thus, the answer is option A.

From NTA/IIT papers: JEE Main 2025 · 2 Apr Shift 1

Question 3 medium

To measure the internal resistance of a battery, potentiometer is used. For

R = 10 Ω

, the balance point is observed at

l = 500 c m

and for

R = 1 Ω

the balance point is observed at

l = 400 c m

. The internal resistance of the battery is approximately :

$0.1 Ω$
$0.3 Ω$
$0.2 Ω$
$0.4 Ω$

Answer: B

Explanation. **Principle:** A potentiometer measures the terminal voltage of the battery. When the battery drives current through an external resistance

R

, its terminal voltage is

V = ε - I r

, where

r

is internal resistance. The balance length is proportional to this terminal voltage. Let

k

be the potential gradient (V/cm). Then:

V = k l = ε - I r

Also, the current is

I = \frac{ε}{R + r}

, so:

k l = ε - \frac{ε r}{R + r} = ε (\frac{R}{R + r})

**Case 1:**

R = 10 Ω

l = 500

cm:

k (500) = ε (\frac{10}{10 + r}) ...(i)

**Case 2:**

R = 1 Ω

l = 400

cm:

k (400) = ε (\frac{1}{1 + r}) ...(ii)

Dividing (i) by (ii):

\frac{500}{400} = \frac{10}{10 + r} \cdot \frac{1 + r}{1}

\frac{5}{4} = \frac{10 (1 + r)}{10 + r}

5 (10 + r) = 40 (1 + r)

50 + 5 r = 40 + 40 r

10 = 35 r ⟹ r = \frac{10}{35} \approx 0.286 Ω \approx 0.3 Ω

The other options (

0.1

0.2

0.4 Ω

) do not satisfy the ratio of balance lengths. Answer: (B)

From NTA/IIT papers: JEE Main 2024 · 4 Apr Shift 1

Question 4 easy

The length of a metallic wire is increased by

20 %

and its area of cross section is reduced by

4 %

. The percentage change in resistance of the metallic wire is __________.

Answer: 25

Explanation. Resistance of a wire is

R = ρ \frac{L}{A}

Let the original length be

L

and area be

A

. New length:

L^{'} = 1.20 L

New area, reduced by

4 %

A^{'} = 0.96 A

New resistance:

R^{'} = ρ \frac{L^{'}}{A^{'}} = ρ \frac{1.20 L}{0.96 A}

So,

\frac{R^{'}}{R} = \frac{1.20}{0.96} = 1.25

Thus,

R^{'} = 1.25 R

Percentage change in resistance:

\frac{R^{'} - R}{R} \times 100 = (1.25 - 1) \times 100 = 25 %

Answer: 25

From NTA/IIT papers: JEE Main 2023 · 6 Apr Shift 1

Question 5 hard

A galvanometer gives full scale deflection with

0.006 A

current. By connecting it to a

4990 Ω

resistance, it can be converted into a voltmeter of range

0 - 30 V

. If connected to a

\frac{2 n}{249} Ω

resistance, it becomes an ammeter of range

0 - 1.5 A

. The value of

n

Answer: 5

Explanation. The galvanometer resistance is

G

, and its full-scale current is

I_{g} = 0.006 A

. For the voltmeter conversion, the series resistance is

R_{v} = 4990 Ω

, and the range is

30 V

30 = I_{g} (G + R_{v}) = 0.006 (G + 4990)

G + 4990 = \frac{30}{0.006} = 5000

G = 10 Ω

For the ammeter conversion, a shunt resistance

S = \frac{2 n}{249} Ω

is connected in parallel. The range is

1.5 A

, so the shunt carries

1.5 - 0.006 = 1.494 A

at full deflection. The voltage across the shunt equals the voltage across the galvanometer:

I_{g} G = (1.5 - I_{g}) S

0.006 \times 10 = 1.494 \times \frac{2 n}{249}

0.06 = \frac{1.494 \times 2 n}{249}

0.06 \times 249 = 2.988 n

14.94 = 2.988 n

n = \frac{14.94}{2.988} = 5

5

From NTA/IIT papers: JEE Advanced 2014

Frequently asked questions

How much of JEE Main comes from Current Electricity?: JEEGenie estimates about 6% of JEE Main marks come from Current Electricity, based on recent papers. The share varies from year to year.
Which formulas matter most in Current Electricity?: The Current Electricity sheet on this page has 24 formula entries, starting with Electric Current, Current Density, Drift Velocity, Ohm's Law, Resistivity and Conductivity. Each one comes with when to use it and the trap to avoid.
What topics does Current Electricity cover for JEE?: Current Electricity covers Ohm's Law and Resistance, Kirchhoff's Laws, Wheatstone Bridge, Cells and EMF, Electrical Power, Potentiometer and Meter Bridge.
How should I revise Current Electricity before the exam?: Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens Current Electricity questions on JEEGenie.
How many previous-year questions are there on Current Electricity?: JEEGenie has 518 previous-year questions on Current Electricity, and this page shows a few with worked explanations.
Is practice on Current Electricity free on JEEGenie?: Sign-up is free and includes a 7-day Pro trial. After the trial, free accounts keep a limited daily quota.