Elec Class

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General electricity the full course in 15 steps

Prepare a general electricity exam: the 15 chapters of the course in order, from Ohm's law to AC circuits, with practice problems and answers. 15 steps · 260 levels · the full course, in order

First levelStep 1 · Ampere-hours to coulombsBasics & units, level 1 of 8
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The 15 steps each step unlocks the next

  1. 1

    1. Basics & units

    8 levelsLesson: Electrical units and conversions

    SI, prefixes, scientific notation, symbols, reading a dial.

    1. 1Ampere-hours to coulombs
    2. 2Kilo-ohms to ohms
    3. 3Kilowatt-hours to joules
    4. 4Milliamperes to amperes
    5. 5Square millimetres to square metres
    6. 6Microfarads to farads
    7. 7Prefixes
    8. 8SI units
  2. 2

    2. Electrostatics

    7 levelsLesson: Electrostatics and Coulomb's law

    Atom, charges, Coulomb, electric field.

    1. 1Charge of the electron
    2. 2Conductor or insulator
    3. 3Coulomb's law and distance
    4. 4Attraction and repulsion
    5. 5Which attract?
    6. 6Field between two plates
    7. 7Force between two charges
  3. 3

    3. Voltage & current

    22 levelsLesson: Voltage and current

    Potential, current direction, Q = I·t, current density, mains.

    1. 1Direct computation of Q
    2. 2Current from Q and t
    3. 3Converting ampere-hours to coulombs
    4. 4The coulomb
    5. 5Potential difference
    6. 6Domestic network
    7. 7Current direction
    8. 8Duration of flow
    9. 9Average current of a battery
    10. 10Cell autonomy
    11. 11Milliampere-hours to coulombs
    12. 12Measure then compute Q
    13. 13Reach a quantity of electricity
    14. 14Predict the quantity of electricity
    15. 15Average current from the counter
    16. 16Where to measure the current?
    17. 17Quantity of electricity
    18. 18Starter: brief high current
    19. 19Cell autonomy on a lamp
    20. 20Number of electrons
    21. 21Battery autonomy
    22. 22Current density
  4. 4

    4. Ohm's law & resistance

    12 levelsLesson: Ohm's law

    Getting started in the lab, U = R·I, Pouillet, temperature, colour code.

    1. 1First resistor
    2. 2The chips
    3. 3The switch
    4. 4The leads
    5. 5Build a resistor circuit and find the current
    6. 6Predict the current
    7. 7Reach 20 mA
    8. 8If the voltage doubles...
    9. 9Resistance of a wire
    10. 10Setting the length of a wire
    11. 11Resistance and temperature
    12. 12E12 series
  5. 5

    5. Power, energy, efficiency

    34 levelsLesson: Electric power

    P = U·I, Joule, kWh, efficiency, lamp and energy meter.

    1. 1Power of a hotplate
    2. 2Energy used by a kettle
    3. 3Running time of an oven
    4. 4Power of a load (U, I)
    5. 5Kilowatt-hours to kilojoules
    6. 660 W / 230 V lamp
    7. 7Watt and joule
    8. 8Resistance from the rating plate
    9. 9Useful energy of a motor
    10. 10Predict the energy used
    11. 11Lamp at its rated power
    12. 12Power in R1
    13. 13Energy meter
    14. 14Electricity bill
    15. 15Power of a load
    16. 16Waterfall, turbine and generator
    17. 17Power of a crane motor
    18. 18Lifting time
    19. 19Efficiency of a goods lift
    20. 20Load a hoist can lift
    21. 21Pump motor
    22. 22Connect a wattmeter
    23. 23P = U·I, checked with the wattmeter
    24. 24Stop at the right time
    25. 25Lamp at another voltage
    26. 26Which one heats up most?
    27. 27Under-supplied lamp
    28. 28Joule heating
    29. 29Mechanical power of a motor
    30. 30Required flow of a waterfall
    31. 31Height of a waterfall
    32. 32Efficiency of a generator
    33. 33Efficiency of a real generator
    34. 34Efficiency of a motor
  6. 6

    6. Resistor networks

    13 levelsLesson: Series and parallel circuits

    Series, parallel, mixed, line drop, troubleshooting.

    1. 1Two resistors in series
    2. 2Voltage sharing
    3. 3Equivalent resistance
    4. 4Two resistors in parallel
    5. 5Branch current
    6. 6Aim for a parallel resistance
    7. 7Mixed circuit
    8. 8n identical resistors in parallel
    9. 9Line voltage drop
    10. 10Two-wire line
    11. 11Mixed network
    12. 12Wrong value
    13. 13Tricky mixed circuit
  7. 7

    7. Measurement & instruments

    12 levelsLesson: Voltmeter and ammeter

    Voltmeter, ammeter, ohmmeter, wattmeter, ranges, upstream / downstream, shunt.

    1. 1The voltmeter
    2. 2Voltmeter on R2
    3. 3Ammeter in series
    4. 4Measure, then conclude
    5. 5Choosing the range
    6. 6Range and needle
    7. 7Ohmmeter rule
    8. 8Measuring a resistance with an ohmmeter
    9. 9Reading a wattmeter
    10. 10Not-so-perfect voltmeter
    11. 11Upstream or downstream connection
    12. 12Shunt calculation
  8. 8

    8. Real generators & loads

    36 levelsLesson: EMF and internal resistance

    E and r, E' and r', generalised Ohm's law, U = f(I) characteristic.

    1. 1Generator in opposition
    2. 2Real generator
    3. 3EMF of an accumulator cell
    4. 4Current delivered by an accumulator
    5. 5External resistance of an accumulator
    6. 6Predict the current of a real cell
    7. 7Voltage needed to recharge an accumulator
    8. 8Maximum charging current
    9. 9EMF of a charging accumulator
    10. 10A cell and its load
    11. 11Internal resistance of an accumulator
    12. 12Ammeter connected straight across a cell
    13. 13Electrical efficiency of a generator
    14. 14Measure the internal resistance of a cell
    15. 15No load, then under load
    16. 16Internal resistance of a charging accumulator
    17. 17Battery of n cells being charged
    18. 18Useful power of a motor
    19. 19Predict the current of a motor
    20. 20Measure the back-EMF of a motor
    21. 21Get the wanted current in a motor
    22. 22Accumulator being charged
    23. 23Two accumulators in opposition
    24. 24Limiting the charging current
    25. 25Rheostat between a generator and a load
    26. 26Two cells in opposition
    27. 27Current drawn by a motor
    28. 28Generalised Ohm's law
    29. 29Active load
    30. 30Voltage under load
    31. 31Load for a given efficiency
    32. 32Generalised Ohm's law: missing EMF
    33. 33Two cells, one motor, two resistors
    34. 34Set the rheostat of a motor
    35. 35Plotting U = f(I)
    36. 36Internal resistance from the slope
  9. 9

    9. Kirchhoff's laws

    12 levelsLesson: Kirchhoff's current and voltage laws

    Junctions, loops, several sources, bridge.

    1. 1Junction rule
    2. 2Current at the junction
    3. 3Two cells in series
    4. 4Missing current
    5. 5Which branch carries the most current?
    6. 6Junction law in the lab
    7. 7Cells in opposition
    8. 8Loop equation
    9. 9Two sources, three branches
    10. 10Two sources on one load
    11. 11Two-source ladder
    12. 12Reproduce a bridge
  10. 10

    10. Capacitors

    17 levelsLesson: Capacitors and RC circuits

    C = Q/U, combinations, energy, marking, time constant.

    1. 1Capacitors in parallel
    2. 2The farad
    3. 3Two capacitors in parallel
    4. 4Capacitors in series
    5. 5Two capacitors in series
    6. 6Completing a capacitance
    7. 7Capacitor marking
    8. 8Charge of a capacitor
    9. 9Time constant
    10. 10Voltage across a series group
    11. 11Missing capacitor of a series group
    12. 12Charge of a parallel group
    13. 13Third capacitor of a parallel group
    14. 14Stored energy
    15. 15Ceq of two capacitors in series
    16. 16Same energy at another voltage
    17. 17Adding a discharged capacitor
  11. 11

    11. Magnetism & electromagnetism

    16 levelsLesson: Magnetism and magnetic force (F = BIL)

    Magnets, B, Φ, coil, Laplace.

    1. 1Field lines
    2. 2Poles of a magnet
    3. 3Magnetic units
    4. 4Flux density at the centre of a coil
    5. 5Flux through a coil
    6. 6Number of turns for a flux density
    7. 7Current for a given flux density
    8. 8Length of a coil
    9. 9Flux of a coil in air
    10. 10Flux with an iron core
    11. 11Laplace force on a conductor
    12. 12North pole of the coil
    13. 13Direction of the Laplace force
    14. 14Coil diameter for a given flux
    15. 15Permeability of a core
    16. 16Turns to spread over a core
  12. 12

    12. Induction & self-induction

    20 levelsLesson: Electromagnetic induction

    Faraday, Lenz, inductance, energy, RL.

    1. 1Faraday's law
    2. 2Lenz's law
    3. 3Conductor sweeping the field lines
    4. 4Self-induced EMF
    5. 5Laplace force
    6. 6Energy of a coil
    7. 7RL time constant
    8. 8EMF induced in a flat coil
    9. 9Speed of a bar in a field
    10. 10Flux density cut by a bar
    11. 11Admissible switch-off time
    12. 12Current cut in a coil
    13. 13Current for a given force
    14. 14Inductance of a coil
    15. 15Self-induction
    16. 16EMF induced in a coil
    17. 17Direction of the induced current
    18. 18Fluxmeter probe
    19. 19Bar on rails and dynamometer
    20. 20Primary current from the secondary EMF
  13. 13

    13. Alternating current

    15 levelsLesson: Alternating current

    Sine wave, ω, f, T, RMS / peak, phase shift.

    1. 1Phase shift
    2. 2RMS value
    3. 3Frequency and period
    4. 4From period to frequency
    5. 5Angular frequency
    6. 6From RMS to peak
    7. 7Angular frequency of a sinusoidal current
    8. 8RMS value read on the oscilloscope
    9. 9RMS EMF of an alternator
    10. 10Phase at a given instant
    11. 11Instantaneous value of a current
    12. 12Peak current from the energy
    13. 13Power from the current amplitude
    14. 14Instantaneous value
    15. 15Kettle: amplitude on the oscilloscope
  14. 14

    14. RLC circuits

    21 levelsLesson: RLC circuits and impedance

    Reactances, impedance, Ohm's law in AC.

    1. 1Heating element on AC
    2. 2Reactance and frequency
    3. 3Resistive wire on AC
    4. 4Current in a pure inductor
    5. 5Current in a perfect capacitor
    6. 6Capacitive reactance
    7. 7Inductive reactance
    8. 8Inductance of a pure coil
    9. 9Capacitance of a pure capacitor
    10. 10Angular frequency from an inductor
    11. 11Angular frequency from a capacitor
    12. 12Impedance of a series RLC circuit
    13. 13Resistor and pure inductor in parallel
    14. 14Resistor and capacitor in parallel
    15. 15Pure inductor and capacitor in parallel
    16. 16Ohm's law in AC
    17. 17Impedance of a series RL circuit
    18. 18Resistance of a circuit of known impedance
    19. 19Total voltage of a series RLC
    20. 20Coil resistance from cos φ
    21. 21Real coil and capacitor in parallel
  15. 15

    15. AC power

    15 levelsLesson: Power factor and AC power

    S, P, Q, cos φ, correction.

    1. 1Power factor
    2. 2Why correct the power factor?
    3. 3Active power
    4. 4Powers of a coil
    5. 5Reactive power
    6. 6Two coils in series
    7. 7Three coils in series
    8. 8Heater and motor at a subscriber
    9. 9Lamps, heater and motor
    10. 10Correction capacitor for a coil
    11. 11Correcting the cos φ of a motor
    12. 12Power factor correction
    13. 13Workshop: tubes, motors and heaters
    14. 14Cos φ of a coil in parallel with a resistor
    15. 15Workshop: capacitor, heater and cos φ

Who is it for?

  • AudienceThe full course in 15 steps, to prepare an exam.
  • Pacethe full course, in order
  • HelpA hint, then the full working, for every problem.
  • EquipmentA browser is enough; the lab is more comfortable on a large screen.

Frequently asked questions about this path

Are there any prerequisites?

The first steps go over the basics; if you're a complete beginner, start with the Discovery path.

Can I skip a step?

Steps unlock in order, but all lessons and all problems remain freely available from the lessons.

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In the device's browser; with a free account, it follows you from one device to another.

Other learning paths

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

Circuit diagram CEI 60617

How does it work?

Each big hole is a circuit node: you push one leg of a component into it. The 4 small holes around it are connected to it: chips and leads plug in there.

  1. Place a component Drag it from the palette: it snaps onto the grid. R rotates it.
  2. Bridge neighbouring holes Pick the jumper chip (or C) and drag on the board: bridged holes become a single node.
  3. Draw a lead For long links and the power supply: from one big hole to another, or to a terminal.
  4. Close the loop The circuit is solved live (Ohm, Kirchhoff) and the diagram follows.

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