What is Electricity? Understanding Current, Voltage, and Power

1. Introduction

Electricity is the movement of charged particles—mainly electrons—through a conductor. It is the foundation of all electronic devices, from light bulbs and motors to computers and smartphones. To understand electronics, you must first grasp three key quantities: current, voltage, and power. These three are interrelated and describe how electrical energy is transferred, controlled, and consumed in a circuit.

2. Electric Current (I)

Symbol: I   Unit: Ampere (A)

Electric current represents the rate of flow of electric charge (Q) through a conductor over time:

I = Q / t

There are two main types of current:

• Direct Current (DC): flows in one direction only (e.g., from a battery).
• Alternating Current (AC): changes direction periodically (e.g., household electricity).

Example

If a 12-volt battery powers a 6-ohm resistor:

I = V / R = 12 / 6 = 2 A

Thus, a current of 2 amperes flows through the resistor.

3. Voltage (V)

Symbol: V   Unit: Volt (V)

Voltage, or electric potential difference, is the driving force that pushes electrons through a circuit. A common analogy compares voltage to water pressure in a pipe — the higher the pressure, the faster the water flows. Likewise, higher voltage “pushes” electrons more strongly, creating higher current (if resistance remains constant).

4. Electrical Power (P)

Symbol: P   Unit: Watt (W)

Power indicates the rate at which electrical energy is converted into another form (such as light, heat, or motion).

The basic formula is:

P = V × I

Other useful forms:

P = I² × R
P = V² / R

These variations help calculate the power dissipated on a resistor, useful when selecting components that can handle a certain load safely.

5. Visualization

The following graph illustrates the relationship between voltage and current for different resistor values, following Ohm’s Law.

You can clearly see that with a larger resistance, the slope (V/I ratio) increases — meaning for the same current, more voltage is required.

6. Practical Examples

1. Choosing a resistor for an LED:Suppose you power an LED (forward voltage 2 V) from a 5 V supply. Desired current = 15 mA (0.015 A).

   R = (V_supply - V_LED) / I = (5 - 2) / 0.015 ≈ 200 Ω

2. Calculating resistor power dissipation:P = I² × R = 0.015² × 200 = 0.045 W → choose at least a 0.25 W resistor for safety.

7. Mini Exercise

Question: A 9 V battery is connected to a 330 Ω resistor. Find the current (I) and the power (P).

Solution:

I = 9 / 330 = 0.0273 A (27.3 mA)
P = 9 × 0.0273 = 0.246 W

8. Conclusion

Understanding current, voltage, and power is essential before diving deeper into circuit analysis or component selection. These are the building blocks of all electrical calculations.

In the next article, we’ll explore Ohm’s Law — the simple but powerful equation that links these three quantities:

V = I × R

References

• Thomas L. Floyd, Electronics Fundamentals: Circuits, Devices, and Applications, Pearson, 2014.
• Robert L. Boylestad & Louis Nashelsky, Electronic Devices and Circuit Theory, Pearson, 2012.

Keywords: electricity basics, what is current, voltage and power explained, Ohm’s Law introduction, electronics for beginners