Electrical Fundamentals
100 Important Sentences
1. Basic Electrical Terms
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Electricity is the flow of electrons through a conductor.
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Electric current is the rate of flow of charge.
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The unit of current is the ampere (A).
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Voltage is the electrical pressure that causes current flow.
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The unit of voltage is the volt (V).
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Resistance opposes the flow of electric current.
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The unit of resistance is the ohm (Ω).
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Power is the rate of doing electrical work.
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The unit of electrical power is the watt (W).
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Energy equals power multiplied by time.
2. Electric Charge and Current
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Electric charge is measured in coulombs (C).
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One coulomb equal one ampere-second.
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Electrons have negative charge and move in conductors.
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Conventional current flows from positive to negative.
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Electron flow direction is opposite to conventional current.
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Static electricity is charge at rest.
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Conductors allow free movement of electrons.
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Insulators resist electron movement.
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Semiconductors conduct under certain conditions only.
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Electric current requires a complete circuit to flow.
3. Ohm’s Law and Circuits
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Ohm’s law: V = I × R.
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If voltage increases, current increases proportionally.
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Current decreases when resistance increases.
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Series circuit current is same in all components.
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Parallel circuit voltage is same across all branches.
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Total resistance in series equals sum of all resistors.
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Total resistance in parallel is always less than smallest resistor.
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Kirchhoff’s voltage law states sum of voltages in a loop equals zero.
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Kirchhoff’s current law states sum of currents entering a junction equals sum leaving.
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Power formula: P = V × I.
4. Electrical Power and Energy
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Electrical energy measured in watt-hours or kilowatt-hours.
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One kilowatt-hour equals 3.6 million joules.
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Efficiency equals output power divided by input power.
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Power loss in resistor equals I² × R.
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Electric fuse protects circuit by melting under overcurrent.
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Circuit breaker opens automatically when current exceeds limit.
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Switch controls current flow manually.
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Ammeter connected in series measures current.
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Voltmeter connected in parallel measures voltage.
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Ohmmeter measures resistance of circuit components.
5. Magnetism and Electromagnetism
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Magnetic materials attract iron, nickel, and cobalt.
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Magnetic field lines travel from north to south outside magnet.
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Magnetic flux is total number of magnetic field lines.
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Unit of magnetic flux is the weber (Wb).
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Magnetic flux density equals flux divided by area.
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Unit of flux density is the tesla (T).
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Right-hand rule shows direction of magnetic field around conductor.
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Electromagnetism is magnetic effect produced by current.
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Solenoid converts electrical energy into magnetic field.
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Relays and contactors operate using electromagnetic coils.
6. Electromagnetic Induction
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Electromagnetic induction produces voltage by changing magnetic field.
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Faraday’s law states induced emf proportional to rate of flux change.
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Lenz’s law states induced emf opposes cause producing it.
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Self-induction occurs when current change induces emf in same coil.
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Mutual induction occurs between two coils placed close together.
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Inductance is ability to oppose change in current.
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Unit of inductance is henry (H).
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Energy stored in inductor equals ½ L × I².
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Induced voltage polarity always opposes current change.
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Alternators generate AC voltage using electromagnetic induction.
7. Capacitance
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Capacitor stores electric charge and energy in electric field.
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Capacitance equals charge divided by voltage (C = Q/V).
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Unit of capacitance is farad (F).
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Dielectric material increases capacitor’s storage ability.
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Series capacitance total is less than smallest capacitor.
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Parallel capacitance total equals sum of all capacitances.
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Energy stored in capacitor equals ½ C × V².
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Capacitor blocks DC but passes AC signals.
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Electrolytic capacitors are polarized and used in DC circuits.
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Ceramic capacitors are non-polar and used in AC circuits.
8. Alternating Current (AC)
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Alternating current changes direction periodically.
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AC waveform is usually sinusoidal.
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Frequency is number of cycles per second in hertz (Hz).
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Period is time taken for one complete cycle.
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Amplitude is maximum value of AC voltage or current.
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RMS value equals 0.707 × peak value for sine wave.
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Average value equals 0.637 × peak value.
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Phase angle is difference in phase between two AC waveforms.
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In pure resistance, current and voltage are in phase.
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In inductive circuit, current lags voltage by 90 degrees.
9. Inductive and Capacitive Reactance
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Inductive reactance (XL) = 2πfL.
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Capacitive reactance (XC) = 1 / (2πfC).
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Reactance opposes change in AC current flow.
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Impedance (Z) is total opposition to AC, combining resistance and reactance.
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Impedance formula: Z = √(R² + (XL − XC)²).
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Power factor = cosine of phase angle between current and voltage.
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Power factor = true power divided by apparent power.
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Lagging power factor indicates inductive load.
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Leading power factor indicates capacitive load.
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Correction capacitors improve lagging power factor.
10. Transformers and Power Systems
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Transformer transfers electrical energy between circuits by magnetic induction.
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Primary winding receives input voltage.
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Secondary winding delivers output voltage.
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Turns ratio determines voltage transformation ratio.
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Step-up transformer increases voltage and reduces current.
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Step-down transformer decreases voltage and increases current.
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Transformer efficiency equals output power divided by input power.
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Core losses include hysteresis and eddy current losses.
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Isolation transformer separates two circuits for safety.
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Autotransformer uses common winding for both primary and secondary.