✦ Class 10 · Science

Electricity

You'll see why a tiny wire can heat up like a stove and how a simple compass can reveal invisible forces!

What this lesson covers

Step by step, in this order.

1Electric current is the rate of flow of charge, measured in amperes (1 C s⁻¹).
2Conventional current is taken from + to –, opposite to electron flow; think of a torch powered by a battery.
3Potential difference (voltage) is work per unit charge, measured in volts; a cell maintains a constant V.
4TRY IT: Build a circuit with a cell, a bulb and a switch; draw it using standard symbols.
5Ohm's law: V = IR. For a 12 V battery and 4 Ω resistor, I = 3 A (straight‑line V‑I graph through the origin).
6Resistance (Ω) opposes current; it rises with length, falls with larger cross‑section, depends on material and temperature.
7Resistivity ρ is a material property; R = ρ l/A. A 1 m copper wire (A = 1 mm², ρ = 1.68×10⁻⁸ Ω·m) has R≈0.017 Ω.
8Series resistors share the same current, R_total = R₁+R₂+R₃ (5 Ω+10 Ω+30 Ω=45 Ω). Parallel resistors share the same voltage, 1/R_total = ∑1/R (≈2.73 Ω).
9Heating effect (Joule’s law) H = I²Rt and electric power P = VI = I²R = V²/R. A 5 A heater (R = 20 Ω) on for 30 s produces H = 5²×20×30 J and P = 500 W.
10A current‑carrying wire creates a magnetic field; Oersted discovered this with a compass. Use the right‑hand thumb rule; a solenoid acts like a bar magnet.

How it looks

This board is from a different Science lesson — yours will look like this. She writes and draws while she explains, and stops to check you followed.

Current is the amount of charge passing a point per second; its unit is ampere.
Voltage is the work needed to move one coulomb of charge; a cell provides a constant voltage.
Ohm's law relates voltage, current and resistance; it holds for metallic conductors at constant temperature.
In series resistances add; in parallel their reciprocals add, giving a lower total resistance.
Electricity bill is calculated in kilowatt‑hours; 1 kWh = 3.6×10⁶ J.
A straight current‑carrying wire creates concentric magnetic field lines; use the right‑hand thumb rule to find direction.

Class 10 Science

Interactive. NCERT-aligned. Any time, anywhere.