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Current Electricity is one of the most heavily asked chapters in JEE Main. Resistance networks, cells with internal resistance, the metre bridge and Kirchhoff’s rules come back year after year. The questions are rarely deep, but they are unforgiving about care — one misread series or parallel branch and the whole answer goes. Ten questions below. Give them ten honest minutes.
What this chapter carries in JEE Main
- Usually 3 questions every year, which is 12 marks.
- Resistance networks and cells with internal resistance are asked every year.
- The metre bridge, Kirchhoff’s rules and power in circuits fill the rest.
What the syllabus says
In the syllabus (Unit 12, Current Electricity): Electric current, drift velocity and mobility and how they relate to current, Ohm’s law, electrical resistance, I–V characteristics of ohmic and non-ohmic conductors, electrical energy and power, resistivity and conductivity, resistors in series and parallel, temperature dependence of resistance, internal resistance, potential difference and emf of a cell, cells in series and parallel, Kirchhoff’s laws and their applications, the Wheatstone bridge and the metre bridge.
Taken out in 2024: the potentiometer, its principle and its applications; the colour code for carbon resistors; resistances of different materials.
Taken from the NTA syllabus for JEE Main 2027. See the full syllabus, unit by unit.
Formulas you must know by heart
| Current and drift velocity | I = neAvd |
| Ohm’s law | V = IR, with R = ρL/A |
| A stretched wire | R ∝ L2 when the volume stays fixed |
| Series and parallel | R = R1 + R2, and 1/R = 1/R1 + 1/R2 |
| Cell with internal resistance | V = E − Ir |
| Kirchhoff’s rules | junction rule from charge, loop rule from energy |
| Wheatstone bridge balance | P/Q = R/S |
| Metre bridge | R/S = l/(100 − l) |
| Power | P = VI = I2R = V2/R |
| Temperature dependence | Rt = R0(1 + αt) |
The line about a stretched wire is a JEE Main favourite. Stretching keeps the volume the same, so the length rises and the area falls together, and the resistance goes as the square of the length — not as the length.
Ten questions. Give yourself ten minutes.
Write your answers down before you scroll. A question you looked up is a question you have not answered.
Q1. If the current through a conductor is doubled, the drift velocity of its electrons
- (a) doubles
- (b) becomes half
- (c) does not change
- (d) becomes four times
Q2. A wire of resistance R is stretched to twice its original length. Its new resistance is
- (a) 2R
- (b) 4R
- (c) R/2
- (d) R/4
Q3. Three resistors of 3 Ω each are joined in parallel. The equivalent resistance is
- (a) 9 Ω
- (b) 3 Ω
- (c) 1 Ω
- (d) 6 Ω
Q4. A cell of emf 2 V and internal resistance 1 Ω is connected across 4 Ω. Its terminal voltage is
- (a) 2 V
- (b) 1.6 V
- (c) 0.4 V
- (d) 1.2 V
Q5. Kirchhoff’s junction rule follows from the conservation of
- (a) energy
- (b) charge
- (c) momentum
- (d) mass
Q6. In a metre bridge with 6 Ω in the left gap, the balance point is at 40 cm. The unknown resistance is
- (a) 4 Ω
- (b) 9 Ω
- (c) 6 Ω
- (d) 12 Ω
Q7. As the temperature of a metallic conductor rises, its resistivity
- (a) increases
- (b) decreases
- (c) stays the same
- (d) falls to zero
Q8. The power dissipated in a resistor R across a potential difference V is
- (a) VR
- (b) V2/R
- (c) V2R
- (d) I2/R
Q9. A 60 W and a 100 W bulb, both rated for 220 V, are joined in series across a 220 V supply. The brighter one is the
- (a) 60 W bulb
- (b) 100 W bulb
- (c) both glow equally
- (d) neither glows at all
Q10. The drift speed of the electrons in a metal wire carrying a steady current is of the order of
- (a) 10⁸ m/s
- (b) 10³ m/s
- (c) 10⁻⁴ m/s
- (d) 10⁻¹² m/s
Answer key, with a hint for each
| Q1 | (a) | I = neAvd, and n, e and A are all fixed for a given wire. |
| Q2 | (b) | The volume stays the same, so the area halves as the length doubles, and R = ρL/A goes up four times. |
| Q3 | (c) | 1/R = 1/3 + 1/3 + 1/3 = 1. |
| Q4 | (b) | I = 2/(4 + 1) = 0.4 A, so V = E − Ir = 2 − 0.4. |
| Q5 | (b) | Charge cannot pile up at a junction, so whatever flows in must flow out. |
| Q6 | (b) | R/S = 40/60, so S = 6 × 60/40. |
| Q7 | (a) | The lattice vibrates more, so the electrons are scattered more often. A semiconductor behaves the opposite way. |
| Q8 | (b) | P = V2/R when the voltage across it is known, and I2R when the current through it is known. |
| Q9 | (a) | In series the current is the same, so the larger resistance uses more power. The 60 W bulb has the larger resistance. |
| Q10 | (c) | Drift speed is about a tenth of a millimetre a second — slower than a walking ant. The bulb still lights at once, because the electric field reaches every electron in the wire almost immediately and they all start moving together. |
Now mark yourself honestly
JEE Main marks the way it marks. Use the same rule here:
- +4 for a right answer
- −1 for a wrong one
- 0 for a blank
So ten questions here are out of 40. In the real paper, 25 Physics questions are out of 100.
If you scored 32 or more, the basics of this chapter are secure. Move to harder questions, not more of these.
If you scored below 24, do not feel bad about it. You have just found out something useful before the exam did. Go back to the formula table above, learn it properly, and sit these ten again tomorrow.
And if you guessed a few and they landed, count those as wrong. A guess that works once will not work in January.
The full chapter, on a clock
Ten questions tell you a little. Twenty-five tell you the truth.
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