This topic covers fundamental concepts of electricity such as voltage, current, resistance, Ohm's Law, and power calculations. Students will learn how these factors interact in electrical systems.
Basics of Electricity – Quick Reference Notes
1. What Is Electricity?
- Definition: A form of energy resulting from the movement of electric charge (usually electrons) through a material.
- Key Concepts:
- Charge – property of particles; comes in positive (+) and negative (–) forms.
- Current – flow of charge, measured in amperes (A).
- Voltage (Potential Difference) – the “push” that drives charge, measured in volts (V).
- Resistance – opposition to current flow, measured in ohms (Ω).
2. Fundamental Units (SI System)
| Quantity |
Symbol |
Unit |
What It Measures |
| Electric charge |
Q |
coulomb (C) |
Amount of charge |
| Current |
I |
ampere (A) |
Rate of charge flow (C/s) |
| Voltage |
V |
volt (V) |
Energy per unit charge (J/C) |
| Resistance |
R |
ohm (Ω) |
Opposition to current |
| Power |
P |
watt (W) |
Rate of energy use (J/s) |
| Energy |
E |
joule (J) |
Work done by electricity |
3. Ohm’s Law
- Formula: ( V = I \times R )
- Voltage = Current × Resistance
- Rearrangements:
- ( I = \frac{V}{R} )
- ( R = \frac{V}{I} )
- Use: Predict how voltage, current, and resistance relate in a simple circuit.
4. Types of Current
| Type |
Symbol |
Description |
Typical Use |
| Direct Current (DC) |
— |
Flows in one direction only |
Batteries, electronics |
| Alternating Current (AC) |
— |
Changes direction periodically (usually sinusoidal) |
Household power, grid |
5. Simple Circuit Elements
| Component |
Symbol |
Function |
| Battery / Power Supply |
– |
Provides voltage (EMF) |
| Resistor |
R |
Limits current, creates voltage drop |
| Switch |
– |
Opens/closes circuit |
| Lamp / Load |
– |
Converts electrical energy to light/heat/mechanical work |
| Capacitor |
C |
Stores electric charge (energy) |
| Inductor |
L |
Stores magnetic energy; opposes changes in current |
6. Series vs. Parallel Circuits
| Feature |
Series |
Parallel |
| Current |
Same through all components |
Splits; each branch gets its own current |
| Voltage |
Divides among components |
Same across all branches |
| Total Resistance |
( R_{total}=R_1+R_2+… ) |
( \frac{1}{R_{total}}=\frac{1}{R_1}+\frac{1}{R_2}+… ) |
| Failure Mode |
One open break stops whole circuit |
Other branches keep working if one fails |
7. Power in Electrical Circuits
- Basic Formula: ( P = V \times I ) (watts)
- Using Ohm’s Law, power can also be expressed as:
- ( P = I^2 \times R )
- ( P = \frac