Labo Élec

electrical lab simulator
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Reminder sheet

Basics & units

Bastaya

Before measuring anything, we must speak the same language: units, prefixes, symbols. This sheet is your dictionary.

Every electrical quantity is measured in the International System: voltage in volts (V), current in amperes (A), resistance in ohms (Ω), power in watts (W), energy in joules (J).

Prefixes avoid zeros: k (10³), M (10⁶), m (10⁻³), µ (10⁻⁶), n (10⁻⁹), p (10⁻¹²). Scientific notation m × 10ⁿ keeps 1 ≤ m < 10; only keep the significant figures the measurement justifies.

Formulas

Usual prefixesk = 10³
m = 10⁻³
µ = 10⁻⁶
n = 10⁻⁹
QuantitySymbolUnit
VoltageUV
CurrentIA
ResistanceRΩ
PowerPW
EnergyWJ
Ampere-hour and kilowatt-hour1 Ah = 3 600 C
1 kWh = 3,6 × 10⁶ J
QuantitySymbolUnit
Quantity of electricityQC
EnergyWJ

Worked example

Convert 4.7 kΩ to ohms, 250 mA to amperes and 0.000 22 F to microfarads, then write 47 000 Ω in scientific notation.

  • 4.7 kΩ = 4.7 × 10³ Ω = 4 700 Ω
  • 250 mA = 250 × 10⁻³ A = 0.25 A
  • 0.000 22 F = 220 × 10⁻⁶ F = 220 µF
  • 47 000 Ω = 4.7 × 10⁴ Ω (a single digit before the point).

Common mistakes

  • Mixing up m (milli, 10⁻³) and M (mega, 10⁶): a factor of a thousand billion.
  • Computing with mA or kΩ in U = R·I: convert to SI units (A, Ω) first, then read the result in V.
  • Copying every digit of the calculator: three significant figures are almost always enough.

IEC symbols

GVoltage source
+Cell / battery
Resistor
Switch
Lamp
VVoltmeter
AAmmeter
MMotor

Frequently asked questions

Why convert to SI units before computing?
The formulas of the course (U = R·I, P = U·I…) are written for volts, amperes and ohms. With kilo-ohms or milliamperes the result is off by a factor of 1 000.
How many significant figures should I keep?
As many as the least precise datum: a 5 % resistor does not justify a current with six decimals. In practice, three figures.

15 exercises in this topic

This chapter is covered by the paths: Discovery, General electricity

All sheets · All formulas · Glossary of electrical quantities · Standard electrical symbols (IEC 60617)

Practise this topic
Simulated time00:00:00
Q = I·t-
W = P·t-

Workbench

Circuit diagram CEI 60617

How does it work?

The perfboard: each big hole is a circuit node. You push a single leg of a component (resistor, lamp...) into it. The 4 small holes around it are connected to it: that is where chips and leads plug in.

  1. Drag a component onto the board: it snaps onto the grid. R rotates it.
  2. To join neighbouring big holes, click Jumper chip in the palette (or C) then drag on the board: a line of chips is laid at once. Bridged holes become a single node.
  3. For long links and for the power supply (placed next to the board), drag a lead from one big hole to another (or to a terminal).
  4. As soon as a loop is closed, the circuit is solved in real time (Ohm + Kirchhoff) and the diagram follows.
  5. Zoom with the wheel (or + / −, two-finger pinch); drag the background to pan, 0 fits the board. The + buttons around the board add a row or a column.

Del delete · R rotate · C chip brush · Esc cancel · wheel zoom · drag the background to pan

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