Ornate Pixels: Electronics

Dear friends, through this article today, we will know in detail about Ohm's Law

It is important to know in detail about Ohm's Law for the convenience of electronic circuit design, transistor biasing, daily electronic device repair, and theoretical calculations of various electronic works.

Special message for physics students: For those who are studying physics or engineering, Ohm's Law is not just a chapter; it is the foundation of all circuit-related concepts. If you understand this law well, you will be able to analyze the results of experiments in the laboratory, explain the behavior of complex circuits, and easily solve higher problems related to thermodynamics and electromagnetism. Therefore, it opens the door not only to electronics but also to the entire applied physics. Therefore, read the entire article carefully and try to understand it.

The most basic knowledge that is essential to working with electronics or electrical circuits is Ohm's Law. Discovered by German physicist Georg Simon Ohm, this law establishes the relationship between the three fundamental quantities of a circuit—voltage, current, and resistance.

Whether you repair an LED TV or design a circuit, if you don't know this law, you will never be able to understand the behavior of the circuit correctly.

What is Ohm's Law?

Simply put, Ohm's Law is: If temperature and other physical conditions remain unchanged, the electric current (Current) flowing through a conductor is proportional to the potential difference (Voltage) across the two ends of the conductor.

That is, if the voltage across a given resistance is doubled, the current will also double.

Proof and Explanation of the Formula According to the Diagram

Figure 1 and Figure 2 of your first diagram demonstrate this basic relationship.

Figure 1: Introduction to Variables

Figure 1 shows a typical circuit diagram, which contains the three main variables or quantities of Ohm's law:

V (Voltage): The voltage across the source or two points of the circuit, in volts (V).

R (Resistance): The opposition to the flow of current, in ohms (Ω).

I (Current): The flow of electrons through the resistor, in amperes (A).

Figure 2: Mathematical Proof

Figure 2 is a mathematical proof of the formula. In this circuit, when a potential difference of 1V is applied across a 1Ω resistor, exactly 1A of current flows. This proves that:

1V=1A×1Ω

A labeled diagram showing the mathematical proof of Ohm's Law, where a 1 Volt source applied across a 1 Ohm resistor results in 1 Ampere of current flow.

Figure 1: Basic circuit diagram illustrating the three fundamental variables of Ohm's Law (V, I, and R).

Therefore, for a current of 1 Ampere to flow in a circuit, a voltage of 1 Volt is required across a resistance of 1 Ohm, which supports Ohm's original statement.

Practical application of Ohm's law in series circuits

Analysis of the diagram

Total resistance (R total): The resistances in a series circuit are simply added together. R total=1Ω+2Ω+3Ω=6Ω.
Total current (I total): The total current is obtained by dividing the total voltage by the total resistance. I=12V/6Ω=2A. A current of 2A will flow through each component in the series circuit.
Voltage drop and node voltage: This diagram proves that the voltage drop across each resistor is proportional to the value of its resistance (i.e., a larger resistor has a larger voltage drop).

A series circuit diagram showing three resistors (1 Ohm, 2 Ohm, 3 Ohm) connected to a 12 Volt source, calculating the total resistance, 2 Ampere total current, and the subsequent voltage drops across each resistor.

Figure 2: Practical application of Ohm's Law for calculating total current and individual voltage drop across resistors in a series circuit.

Three forms of Ohm's law and the relationship between power (Watts)

Ohm's law is used in three forms, which help to find any unknown quantity in a circuit. Along with these formulas, it is also necessary to know the formulas for another very important quantity in electronics, power (Power) or watts:

Main formula and units

Quantity	Formula	Unit
Voltage (V)	V = I × R	Volt (V)
Current (I)	I = V / R	Ampere (A)
Resistance (R)	R = V / I	Ohm (Ω)
Power (P)	P = V × I or P = I² × R	Watt (W)

Why is it important to know the power?

In an LED TV circuit, it is crucial to know both the resistance value (in Ohms) and the power rating (in Watts) of the resistors you use.

The power dissipated by a resistor can be calculated using the formula P = I² × R, where I is the current and R is the resistance.

This power is released as heat. To prevent overheating or damage, you must choose a resistor whose wattage rating exceeds the calculated power dissipation.

Why is it important to know Ohm's Law?

The main reasons why Ohm's Law is called the foundation of electronics are:

Safe troubleshooting: When repairing a circuit, measuring the voltage and resistance with a multimeter allows for quick calculation of whether excess current is flowing in any part.

Component protection: Ohm's law helps in selecting the correct value of fuses, resistors, and other protective components, which protect the circuit from excess current.

Example: Selecting the right Circuit Breaker

Suppose there are four 15-watt bulbs and three 75-watt fans in a room. How many amperes of fuses or circuit breakers should be used in this room? It is very easy to calculate using Ohm's law.

Calculation Steps (I = P/V):

Supply Voltage (V) = 220V
Bulbs: 15W × 4 = 60W
Fans: 75W × 3 = 225W
Total Power (P) = 60W + 225W = 285W

Total Current (I):

I = 285W / 220V = 1.295A

Important Note on Selection: Although the calculated current is 1.295A, in practical electrical work, a fuse or circuit breaker must be selected with a 25% safety margin to account for inrush current (when loads are first turned on).
Calculation with Margin: 1.295A × 1.25 ≈ 1.62A.
Therefore, a standard 2A or 3A circuit breaker should be used to ensure the circuit's safety.

Future Prediction: Before changing the load in an electrical circuit, the effect on the rest of the circuit can be mathematically predicted using Ohm's law.

Practical Example: Resistor Calculation for a 5mm LED

This example proves why knowing Ohm's Law is essential. It's used to protect sensitive components like LEDs from excess current.

A circuit diagram showing a 5V battery, a current-limiting resistor, and an LED, illustrating the 0.02A safe current flow calculated using Ohm's Law.

Figure 3: A practical circuit diagram demonstrating how a 150Ω current-limiting resistor ensures safe operation for a 5mm LED from a 5V supply, maintaining a 20mA current as calculated by Ohm's Law.

Setup and Key Variables

Quantity	Value	Explanation
Supply Voltage (V_s)	5V	The total voltage provided by the power source.
LED Forward Voltage (V_f)	2V	The required voltage for the LED to safely illuminate.
Desired Current (I)	20mA (0.02A)	The standard, safe operating current for most 5mm LEDs.

Step-by-step Calculation

The resistor must absorb the excess voltage remaining after the LED takes its required 2V. We calculate the required voltage drop (V_r) across the resistor:

V_r = V_s - V_f
V_r = 5V - 2V = 3V

Now, using Ohm's Law (R = V/I) with V_r and the desired current I:

R = V_r / I
R = 3V / 0.02A = 150Ω

Final Answer & Wattage Check

To operate the LED safely, you must use a 150Ω resistor in series.

The resistor must also handle the dissipated power (P). P = V_r × I = 3V × 0.02A = 0.06W. Therefore, a common 0.25W (or 1/4W) resistor is more than sufficient.

Ohm's Law, the Basics of Electronics