What current really is, why thin long wires resist more, and how series and parallel change everything — with the formulas you can prove on a slider.
Play with it
Drag the voltage and resistance and watch the current change — double V and the current doubles; double R and it halves. That's V = IR.
I = V / R = 2.00 A — double the voltage and the current doubles; double the resistance and it halves.
Learn
Electric current is the rate of flow of electric charge through a conductor. If charge Q flows in time t, the current is I = Q/t. A closed loop that lets charge flow is a circuit; if it breaks anywhere, the current stops.
By convention, current flows from the + terminal to the − terminal (opposite to the actual electron flow).
I = Q / t
SI unit: ampere (A). 1 A = 1 coulomb per second.
Charges flow only when there is a potential difference (V) across the conductor — supplied by a cell or battery. It is the work done to move a unit charge between two points: V = W/Q.
A voltmeter measures potential difference and is always connected in parallel across the component; an ammeter measures current and is connected in series.
V = W / Q
SI unit: volt (V). 1 V = 1 joule per coulomb.
At constant temperature, the current through a conductor is directly proportional to the potential difference across it: V ∝ I, so V = IR. The constant R is the resistance. A graph of V against I is a straight line through the origin, and its slope is R.
V = I × R
Resistance R in ohms (Ω); 1 Ω = 1 V/A.
Use the Ohm's-law explorer at the top of the page to see V = IR in action — drag the voltage and resistance and watch the current respond.
The resistance of a wire depends on four things:
R = ρ L / A
Resistivity ρ (ohm-metre) is a property of the material — low for copper, high for nichrome.
Connecting wires use copper/aluminium (low ρ, little heat wasted); heating elements use nichrome (high ρ, gets hot on purpose).
Series: components share one path. The same current flows through each, and resistances add: R = R₁ + R₂ + R₃. One break stops everything.
Parallel: components sit on separate branches with the same voltage across each, and 1/R = 1/R₁ + 1/R₂ + … The total resistance is less than the smallest branch. Homes use parallel so every appliance gets the full 220 V and can switch independently.
From a 6 V battery: equivalent resistance and total current shown above.
When current flows through a resistor, electrical energy turns into heat — the heating effect. Joule's law: H = I²Rt. This runs heaters, irons, and the filament of a bulb.
Electric power is the rate of using energy: P = VI = I²R = V²/R. Energy used = power × time. The bill is charged in kilowatt-hours (kWh) — "1 unit".
P = VI = I²R = V²/R
1 kWh = 1000 W for 1 hour = 3.6 × 10⁶ J.
Why this matters
Every switch you flick and every electricity bill you pay is this chapter in action — Ohm's law, parallel circuits and power are wired into your home.
Every plug point sits in parallel, so each appliance gets the full 220 V and any one can switch on or off without touching the rest. Wire them in series and adding a second bulb would dim them both — and one failing would kill the whole line.
Parallel circuitsYour meter charges for energy in units (kWh). A 1000 W geyser run for 2 hours uses 1000 × 2 = 2000 Wh = 2 units; multiply by the per-unit rate for the cost. P = VI and energy = P × t are exactly what the meter is counting.
Power & energy (kWh)A fuse is a thin wire that melts when the current (and its I²R heat) gets dangerously high — cutting the circuit to prevent fires.
Heating appliances use Joule's law H = I²Rt — a high-resistance element turns electrical energy into heat.
Power travels long distances at very high voltage to keep the current — and the I²R losses — low.
Fuses, heating appliances, power transmission and more — each explained with a diagram. Free to unlock.
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Modelled on CBSE's competency-based pattern — MCQ, assertion–reason and case-study items, the kind that now make up about half your board paper.
Interactive explainers hand-built for trykarkedekho. Content from the rationalised NCERT Class 10 Science syllabus (ncert.nic.in).
Buffyyour study buddy Buffy is an AI helper and can be wrong — always check your NCERT textbook.