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NEET UG · Physics · chapter
Current Electricity questions in NEET come to about three to five of the forty-five Physics questions, and nearly all of them are procedural: reduce the network, apply a rule, substitute. This guide gives the formulas worth memorising, the bridge and potentiometer conditions, the five mistakes that cost the most marks, a free quiz and worked examples.
Quick answer
Questions per paper
3–5
Of 45 Physics questions · BrainStride analysis of past papers
Question style
Circuit reduction
Numerical, one or two steps each
Class
12
Builds on electrostatics and basic algebra
Marks at stake
Up to 20
At +4 each, before negative marking
BrainStride analysis of past papers
Current as charge per unit time, and the microscopic picture behind it: electrons drifting slowly against a lattice. Resistivity depends on the material and its temperature, never on the length or the cross-section — that distinction is worth marks on its own.
Series adds resistances, parallel adds conductances. Most NEET questions are a reduction problem with a one-line calculation at the end, so the marks go to whoever reduces the network correctly.
Terminal voltage falls below the emf as soon as current flows. Cells in series add emfs, and identical cells in parallel keep the emf but divide the internal resistance.
The junction rule is conservation of charge; the loop rule is conservation of energy. Fix a sign convention before writing any loop equation and keep it for the whole problem.
At balance no current flows through the galvanometer and the ratio condition holds. The metre bridge is the same condition written with lengths, which is why a balance point at 40 cm tells you a resistance without measuring any current.
The one instrument that measures emf rather than terminal voltage, because it draws no current from the cell at balance. Questions test that idea more often than the arithmetic around it.
Power as VI, I²R or V²/R — choose the form whose quantities you already know. Converting a galvanometer into an ammeter needs a shunt in parallel; into a voltmeter, a high resistance in series.
V = IR
Valid for ohmic conductors at constant temperature.
R = ρL/A
Stretching a wire keeps its volume constant, so R ∝ L² — a favourite trick.
I = nAevᵈ · vᵈ = eEτ/m
Drift speeds are of the order of 10⁻⁴ m/s, far slower than the signal itself.
J = I/A = σE
The vector form of Ohm’s law, with σ the conductivity.
Series: R = R₁ + R₂ + … · Parallel: 1/R = 1/R₁ + 1/R₂ + …
n identical resistors R in parallel give R/n.
V = ε − Ir
Equal to the emf only when no current is drawn, which is why a potentiometer measures emf.
P = VI = I²R = V²/R
In series the largest resistance dissipates most power; in parallel, the smallest.
P/Q = R/S at balance
At balance the galvanometer carries no current, so it can be ignored while reducing the rest.
R/S = l/(100 − l)
l is the balancing length in centimetres measured from the left end.
ε₁/ε₂ = l₁/l₂
Only valid while the driver cell’s emf exceeds both cells being compared.
ρ = ρ₀[1 + α(T − T₀)]
Positive α for metals; semiconductors behave the other way.
Ammeter: S = IᶢG/(I − Iᶢ) · Voltmeter: R = V/Iᶢ − G
A shunt in parallel for an ammeter, a high resistance in series for a voltmeter.
Why it happens
Resistors that look adjacent in the drawing are assumed to be in series or parallel without checking the nodes.The fix
Label every node before reducing. Two resistors are in parallel only when both ends sit at the same pair of nodes; redraw the circuit with the nodes spread out if the figure hides it.Why it happens
The cell is treated as an ideal source once the external network looks complicated.The fix
Write the total resistance as external plus internal before finding the current, then get the terminal voltage from V = ε − Ir.Why it happens
Both are called "resistance" in speech, so a question about stretching a wire gets answered as though ρ changed.The fix
Remember what each depends on: ρ on material and temperature, R also on length and area. In a stretching problem, volume stays constant and R ∝ L².Why it happens
Kirchhoff's loop equations are written while reading the figure, so the sign flips when the direction of travel changes.The fix
Mark the assumed current direction and the traversal direction on the figure first, then apply the same rule to every element. A negative answer simply means the current runs the other way.Why it happens
It is revised as another way to measure voltage, so the no-current condition gets forgotten.The fix
State the condition every time: at balance the cell drives no current, so the reading is the emf, and the driver cell must have the larger emf for a balance point to exist at all.6 questions
Question 1
A wire of resistance R is stretched to twice its original length, with its volume unchanged. Its new resistance is:
Question 2
Three resistors of 6 Ω each are connected in parallel. The equivalent resistance is:
Question 3
A cell of emf 2 V and internal resistance 0.5 Ω is connected across a 3.5 Ω resistor. The current in the circuit is:
Question 4
At the balance point of a Wheatstone bridge:
Question 5
If the same current flows through a conductor whose cross-sectional area is doubled, the drift velocity of the electrons:
Question 6
The resistivity of a metallic conductor depends on:
A test on one chapter alone tells you little — the exam never asks Current Electricity in isolation. So this builds a full NEET Physics paper that leans on it. Weighted like the exam, a 45-question paper gives Current Electricity 4 questions; marked weak, it gets 8, and the rest of the paper keeps the other chapters honest. Fill the plan from previous-year questions or your module.
Your paper
Press Generate paper plan for a chapter-by-chapter blueprint: questions per chapter, numericals, marks and time — ready to print and fill from your PYQs, modules or the BrainStride question bank.
Chapter weights are BrainStride’s reading of past papers, not official data. For any other chapter mix, use the NEET Physics test generator.
Single-step numerical · metre bridge
In a metre bridge, the balance point is found at 40 cm from the left end when a 6 Ω resistance is connected in the right gap. What is the unknown resistance in the left gap?
Answer: The unknown resistance is 4 Ω.
Two-step numerical · cell with internal resistance
A cell of emf 2 V and internal resistance 0.5 Ω is connected to an external resistance of 3.5 Ω. Find the current, the terminal voltage and the power delivered to the external resistor.
Answer: The current is 0.5 A, the terminal voltage 1.75 V and the external power 0.875 W.
Single-step numerical · drift velocity
A copper wire of cross-sectional area 1 × 10⁻⁶ m² carries a current of 1.6 A. If the free electron density is 8 × 10²⁸ m⁻³, find the drift velocity. Take e = 1.6 × 10⁻¹⁹ C.
Answer: The drift velocity is 1.25 × 10⁻⁴ m/s — a fraction of a millimetre per second, which is why the current starts long before any electron crosses the wire.
In recent NEET papers, Current Electricity has carried about 3 to 5 of the 45 Physics questions. That is BrainStride’s analysis of past papers rather than an official figure, since NTA publishes no chapter-wise weightage. It is consistently one of the heavier Physics chapters, alongside electrostatics and modern physics.
Yes, more than most of Physics. The questions are procedural rather than conceptual traps: reduce the network, apply Ohm’s law or Kirchhoff’s rules, substitute. Students who practise circuit reduction deliberately tend to convert almost every question here, which is not true of mechanics.
Emf is the potential difference across a cell when it drives no current; terminal voltage is what you measure while current flows, given by V = ε − Ir. The two are equal only in an open circuit, which is exactly why a potentiometer, which draws no current at balance, measures emf directly.
Label the nodes before touching the resistors. Two resistors are in parallel only if both their ends meet at the same two nodes, which is often hidden by how the figure is drawn. Redrawing the circuit with the nodes spread apart takes twenty seconds and removes the most common error in the chapter.
Ohm’s law with series and parallel combinations, R = ρL/A with the stretched-wire result R ∝ L², terminal voltage V = ε − Ir, the three power forms, the Wheatstone balance condition and the metre bridge length ratio. Drift velocity appears as a single-step substitution.
Only lightly. Current Electricity assumes comfort with electrostatics ideas such as potential difference, and with ratios and simultaneous equations. It needs no calculus, which makes it one of the first Class 12 chapters a dropper can rebuild confidence on.
The 20-minute diagnostic shows whether your Physics marks leak here or in mechanics, then writes the practice for it. Free, no card.