This topic covers essential electrical concepts such as voltage, current, resistance, and power, providing a foundation for understanding electronics.
Understanding Basic Electrical Concepts
Quick reference guide for students, hobbyists, and anyone new to electricity.
1. Fundamental Quantities
| Symbol |
Quantity |
Unit |
Common Symbolic Representation |
| V |
Voltage (Electric potential difference) |
Volt (V) |
V = W / C |
| I |
Current (Flow of charge) |
Ampere (A) |
I = Q / t |
| R |
Resistance (Opposition to current) |
Ohm (Ω) |
R = V / I |
| P |
Power (Rate of energy transfer) |
Watt (W) |
P = V·I = I²R = V²/R |
| C |
Capacitance (Ability to store charge) |
Farad (F) |
C = Q / V |
| L |
Inductance (Ability to store magnetic energy) |
Henry (H) |
L = Φ / I |
2. Ohm’s Law
- Formula: ( V = I \times R )
- Interpretation: The voltage across a resistor is proportional to the current flowing through it.
- Usage: Solve for any one variable when the other two are known.
3. Power Relationships
| Situation |
Formula |
When to Use |
| General power |
( P = V \times I ) |
Any circuit |
| Resistive load |
( P = I^{2}R ) |
Known current & resistance |
| Voltage‑driven |
( P = \dfrac{V^{2}}{R} ) |
Known voltage & resistance |
4. Series vs. Parallel Circuits
4.1 Series Connection
- Current: Same through all components.
- Voltage: Splits proportionally to resistance.
- Total Resistance: ( R_{\text{total}} = R_{1}+R_{2}+...+R_{n} )
4.2 Parallel Connection
- Voltage: Same across each branch.
- Current: Splits inversely proportional to resistance.
- Total Conductance: ( \frac{1}{R_{\text{total}}}= \frac{1}{R_{1}}+\frac{1}{R_{2}}+...+\frac{1}{R_{n}} )
5. Energy and Charge
- Charge (Q): Measured in coulombs (C). 1 C = 1 A·s.
- Energy (W): Measured in joules (J). 1 J = 1 W·s.
- Relationship: ( W = V \times Q ) (energy delivered by a voltage source moving charge Q).
6. Basic Passive Components
| Component |
Symbol |
Primary Function |
Typical Equation |
| Resistor |
R |
Limits current, drops voltage |
( V = I R ) |
| Capacitor |
C |
Stores electric field energy |
( I = C \dfrac{dV}{dt} ) |
| Inductor |
L |
Stores magnetic field energy |
( V = L \dfrac{dI}{dt} ) |
| Diode |
— |
Allows current in one direction |
( I \approx I_S (e^{V_D |