NEET Physics · Current Electricity
Ohm's Law
Circuit Lab
Drag resistors, change voltage — watch current, power and voltage drops update in real time. Built for NEET exam mastery.
Section 1 of 5 · Foundations
What you'll master in this lab
Four interactive sections take you from Ohm's Law fundamentals to complex series-parallel combinations — the exact circuit problems NEET sets every year.
⚡
Ohm's Law — liveChange V or R and instantly see I = V/R update — with animated current flow in the circuit.
🔗
Series circuitsUnderstand why R_total = R₁+R₂ and why current is the same everywhere but voltage splits.
⬛
Parallel circuitsSee why 1/R = 1/R₁+1/R₂ and why voltage is equal but current splits across branches.
🎯
NEET traps flaggedEvery section calls out the most common wrong answers — with the correct reasoning.
Voltage V (Volts)
Current I (Amperes)
Resistance R (Ohms)
Power P (Watts)
I = V / R Cover I → see V/RV = I × R Cover V → see I×RR = V / I Cover R → see V/IP = V × I = I² R = V²/ROhm's Law
V = I × R
Voltage across a conductor is directly proportional to the current through it, provided temperature is constant. The constant of proportionality is resistance R.
Power Formulae
P = VI = I²R = V²/R
All three are equivalent via Ohm's Law. Use P = I²R when I and R are known; P = V²/R when V and R are known; P = VI always works.
Series Rule
R_eq = R₁ + R₂ + …
Resistors in series: same current flows through each. Total resistance is the sum. Voltage divides in proportion to resistance.
Parallel Rule
1/R_eq = 1/R₁ + 1/R₂
Resistors in parallel: same voltage across each. Reciprocal of total = sum of reciprocals. Current divides inversely to resistance.
Section 1 of 5
Section 2 of 5 · Series Circuit
Series Circuit — Same current, voltage splits
In a series circuit all components share the same current. Voltage divides across resistors in proportion to their resistance. Drag the sliders to see everything update live.
1
Set voltage & resistorsUse sliders to set V (1–30 V) and two resistors R₁, R₂ (1–100 Ω). Watch the circuit update live.
2
Read the metersAll four quantities — total current I, total resistance R, power P, and voltage drops V₁ and V₂ — update instantly.
3
Watch electron flowAnimated dots show current direction and speed. Faster dots = larger current.
Series Circuit Lab
Series Circuit
R₁ and R₂ connected end-to-end
Voltage (V)
12 V
Resistor R₁
10 Ω
Resistor R₂
20 Ω
Current I
—
Amperes
R_total
—
Ohms
Power P
—
Watts
V₁ / V₂
—
Volts each
—
Series circuit rules — step by step
Total resistance: R_total = R₁ + R₂. Resistors in series simply add. Each extra resistor makes it harder for current to flow.
Same current everywhere: I = V / R_total. The same current passes through R₁ and R₂ — there is only one path.
Voltage divides: V₁ = I × R₁ and V₂ = I × R₂. Each resistor "uses" some voltage proportional to its resistance. V₁ + V₂ = V.
Power splits: P₁ = I²R₁ and P₂ = I²R₂. The larger resistor dissipates more power. Total P = P₁ + P₂ = I²R_total.
Key ratio: V₁/V₂ = R₁/R₂ — voltage drops in proportion to resistance. This is the voltage divider rule.
NEET TIPIn series circuits, adding more resistance always reduces current. If one resistor is removed (open circuit), I = 0 for the entire circuit. If short-circuited (R=0), that element has zero voltage drop and total R decreases.
Section 2 of 5
Section 3 of 5 · Parallel Circuit
Parallel Circuit — Same voltage, current splits
In a parallel circuit all branches share the same voltage. Current divides across branches inversely proportional to resistance. The equivalent resistance is always less than the smallest branch resistance.
1
Adjust voltage & both branchesSet V and each parallel branch resistance. Notice R_eq is always smaller than either R₁ or R₂.
2
Watch current splitElectrons flow through both branches simultaneously. The lower resistance branch carries more current — watch the dot speeds differ.
3
Check I₁ + I₂ = I_totalKCL (Kirchhoff's Current Law) — current entering a junction equals current leaving it.
Parallel Circuit Lab
Parallel Circuit
R₁ and R₂ connected across the same two nodes
Voltage (V)
12 V
Branch R₁
10 Ω
Branch R₂
20 Ω
I_total
—
Amperes
R_eq
—
Ohms
Power P
—
Watts
I₁ / I₂
—
Amps each
—
Parallel circuit rules — step by step
Equivalent resistance: 1/R_eq = 1/R₁ + 1/R₂ → R_eq = R₁R₂/(R₁+R₂). Always less than either branch. More paths = less total resistance.
Same voltage across both: V₁ = V₂ = V. Every parallel branch shares the full supply voltage. This is the defining feature of parallel connection.
Current divides: I₁ = V/R₁ and I₂ = V/R₂. The branch with lower resistance carries more current. I_total = I₁ + I₂ (KCL).
Power in each branch: P₁ = V²/R₁ and P₂ = V²/R₂. Lower resistance → more power dissipated. P_total = P₁ + P₂.
Current divider rule: I₁/I₂ = R₂/R₁ — current ratio is the inverse of resistance ratio (opposite of voltage divider).
NEET TIPIn parallel, adding more branches always reduces R_eq and increases total current. For two equal resistors R in parallel: R_eq = R/2. For n equal resistors: R_eq = R/n. If one branch is open-circuited, the other still works — unlike series.
Section 3 of 5
Section 4 of 5 · Combination Circuit
Combination — R₁ in series with (R₂ ∥ R₃)
The most common NEET circuit type: one resistor in series with two in parallel. Solve by first finding the parallel equivalent, then adding the series resistor. Sliders update the full analysis live.
1
Three resistors, one circuitR₁ is in series. R₂ and R₃ are in parallel with each other, and that combination is in series with R₁.
2
Watch the solve stepsStep 1: find R₂₃ = R₂R₃/(R₂+R₃). Step 2: R_total = R₁ + R₂₃. Step 3: find I, then V drops.
3
Check all quantitiesVerify V₁ + V₂₃ = V. Verify I₂ + I₃ = I_main through R₁.
Combination Circuit Lab
R₁ series + (R₂ ∥ R₃)
Combination of series and parallel connections
Voltage (V)
12 V
R₁ (series)
4 Ω
R₂ (parallel)
6 Ω
R₃ (parallel)
12 Ω
I (main)
—
Amperes
R_total
—
Ohms
Power P
—
Watts
V₁ / V₂₃
—
Volts
—
Combination circuit — systematic solution
Find parallel equivalent R₂₃: 1/R₂₃ = 1/R₂ + 1/R₃ → R₂₃ = R₂R₃/(R₂+R₃). This replaces the parallel pair with one equivalent resistor.
Find total resistance: R_total = R₁ + R₂₃. Now the circuit is a simple series circuit with two elements.
Find main current: I = V / R_total. This current flows through the battery and through R₁ (the series element).
Find voltage drops: V₁ = I × R₁ (across R₁) and V₂₃ = I × R₂₃ (across the parallel pair). Check: V₁ + V₂₃ = V.
Find branch currents: I₂ = V₂₃/R₂ and I₃ = V₂₃/R₃. Check: I₂ + I₃ = I (KCL at the junction).
NEET strategy: Always reduce from innermost combination outward. Identify series/parallel groups step by step. Never try to solve the whole circuit at once.
NEET TIPThe current through R₁ equals the total circuit current (series element). The voltage across R₂ equals the voltage across R₃ (parallel elements). These two facts together unlock any combination problem.
Section 4 of 5
Section 5 of 5 · Revision Sheet
Quick Reference — Formulae & Rules
Every formula, rule, and NEET trap for Current Electricity in one place. Screenshot this and use it as your last-minute revision card.
All Formulae
| Quantity | Formula 1 | Formula 2 | Formula 3 |
|---|---|---|---|
| Current I | I = V / R | I = P / V | I = √(P/R) |
| Voltage V | V = I × R | V = P / I | V = √(PR) |
| Resistance R | R = V / I | R = V² / P | R = P / I² |
| Power P | P = V × I | P = I² × R | P = V² / R |
| Series R_eq | R_eq = R₁ + R₂ + R₃ + … (always greater than any individual R) | ||
| Parallel R_eq | 1/R_eq = 1/R₁ + 1/R₂ + … (always less than the smallest R) | ||
| Two parallel | R_eq = R₁R₂ / (R₁ + R₂) — the "product over sum" shortcut | ||
| n equal resistors series | R_eq = nR | ||
| n equal resistors parallel | R_eq = R/n | ||
Series vs Parallel — Key Differences
| Property | Series | Parallel |
|---|---|---|
| Current | Same through all elements I₁ = I₂ = I | Divides: I = I₁ + I₂ |
| Voltage | Divides: V = V₁ + V₂ | Same across all branches V₁ = V₂ = V |
| R_equivalent | Increases (R_eq > any single R) | Decreases (R_eq < any single R) |
| If one breaks (open) | Entire circuit stops (I = 0) | Other branches continue working |
| If one short-circuits (R=0) | That element has 0 V; rest unchanged | Entire circuit short: R_eq = 0 ⚠️ |
| Power distribution | More R → more P (P = I²R) | Less R → more P (P = V²/R) |
| Real-world use | Christmas lights (old), fuses | Home wiring, appliances |
NEET Traps — Memorise These
TRAP 1Parallel R_eq is NOT R₁+R₂. The reciprocal rule 1/R = 1/R₁ + 1/R₂ means R_eq = R₁R₂/(R₁+R₂) — always LESS than either branch.
TRAP 2In series, more R = less I = less P. Counterintuitively, a larger resistor in a series circuit dissipates more power individually but reduces the whole circuit's current.
TRAP 3Rated power vs actual power. A bulb rated 60W at 220V in a different voltage will deliver different power. P_actual = V_actual²/R, not the rated value.
TRAP 4Equal resistors in parallel: R_eq = R/2 (not R/√2 or 2R). n equal resistors in parallel always give R_eq = R/n.
TRAP 5KCL at junctions: Current INTO a node = current OUT. Never add currents around a loop — that's KVL (voltage). Mixing these up causes wrong answers.
TRAP 6Ohm's Law validity: V = IR holds only for ohmic conductors at constant temperature. Diodes, filament bulbs, and thermistors are non-ohmic — their I-V graphs are not straight lines.
Section 5 of 5 · Complete!