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Charle’s Law

What is Charle’s Law?

Charle’s Law, also known as the Law of Volumes, states that at constant pressure, the volume of a given amount of gas is directly proportional to its absolute temperature. In simpler terms, as the temperature of a gas increases, its volume will expand, and conversely, as the temperature decreases, the volume will contract.

Charle's Law

Explanation: Charle’s Law

Imagine you have a balloon, and you are going to see how it behaves when you change the temperature. That is where Charle’s Law comes in!

Charle’s Law:
Charle’s Law is like a special rule for balloons, telling us how they react when things get hot or cold. It says that if you keep the pressure the same (meaning the balloon isn’t squished or pulled), and then you heat it up, the balloon gets bigger.

Balloon Experiment:
Picture this: You have a balloon at room temperature, and it’s a certain size. Now, if you take that balloon and heat it up (maybe with a hairdryer), you will see it gets bigger. Charle’s Law helps us understand that when you heat a balloon at a constant pressure, the size of the balloon increases.

Simple Idea:
Think of your balloon as a bit like a superhero. When it gets warmer, it wants to stretch and grow a bit. The gas particles inside the balloon start moving faster and need more space, so the balloon expands.

Formula (Kind of):
If we want to sound a bit like scientists, Charle’s Law can be written as ( VT ), where (V) is the volume of the balloon, and (T) is the temperature. It’s like saying, “When you heat a balloon at a constant pressure, the volume increases.”

In simpler terms, Charle’s Law helps us predict what happens to a balloon when we warm it up while keeping the pressure the same. It’s like understanding how our balloon friend reacts to changes in temperature.

The History of Charle’s Law

The law is named after Jacques Alexandre César Charles, a French physicist and inventor who first formulated this gas law in the late 18th century. Charles, along with Joseph Louis Gay-Lussac, played a crucial role in the development of modern gas laws. His pioneering work laid the foundation for understanding the behaviour of gases under varying conditions.

Charle’s Law Formula

Mathematically, Charle’s Law can be represented by the equation:

V1 / T1 = V2 / T2


  • V1 and V2 are the initial and final volumes of the gas, respectively.
  • T1 and T2 are the initial and final absolute temperatures of the gas, measured in Kelvin.

The Importance of Absolute Temperature (Kelvin)

Before we proceed further, it is vital to grasp the concept of absolute temperature, which is measured in Kelvin (K). Unlike Celsius or Fahrenheit scales, the Kelvin scale starts from absolute zero, where all molecular motion ceases. It is crucial to use Kelvin in gas law calculations to avoid negative values and ensure accurate results.

Understanding the Behavior of Gases

To comprehend Charle’s Law better, let’s explore how gases behave under different temperature conditions:

  1. Gas Expansion with Heat

When you heat a gas, the energy is transferred to its molecules, causing them to move with higher kinetic energy. As a result, the gas molecules collide more frequently with the container walls, exerting greater pressure and causing the volume to increase.

  1. Gas Contraction with Cooling

On the contrary, when you cool a gas, its molecules lose kinetic energy, reducing the frequency of collisions with the container walls. This leads to a decrease in pressure and, consequently, a contraction in volume.

The Charle’s Law Apparatus

To conduct experiments and validate Charle’s Law, scientists and researchers use a Charle’s Law apparatus. This apparatus typically consists of a graduated cylinder with a movable piston and a temperature sensor. By manipulating the temperature and measuring volume changes, they can observe the direct relationship between volume and temperature.

Real-World Applications of Charle’s Law

Charle’s Law has significant applications in various industries and everyday scenarios. Let’s explore some practical implementations:

1. Hot Air Balloons: Taking Flight with Physics

Hot air balloons operate on the principle of Charle’s Law. When the air inside the balloon is heated, it becomes less dense than the surrounding air, causing it to rise. As the balloon ascends, the temperature drops, and the gas cools, leading to a decrease in volume. To maintain altitude, the pilot can control the burners to maintain a steady temperature and volume.

2. Scuba Diving: Breathable Depths

Scuba divers depend on Charle’s Law to breathe underwater comfortably. As they descend into deeper waters, the pressure increases, causing the volume of the compressed air in their tanks to decrease. Regulators adjust the airflow to match the changing volume, allowing divers to breathe at any depth.

3. Aerosol Cans: Spraying Science

Aerosol cans, such as spray paints and deodorants, use Charle’s Law to release their contents. The propellant gas inside the can expands with heat, increasing pressure and forcing the product out when the nozzle is pressed.

4. Air Conditioning and Refrigeration: Cooling Effect

Air conditioning and refrigeration systems rely on Charle’s Law to cool indoor spaces and preserve perishable items. The refrigerant inside the system expands and contracts, absorbing heat from the surroundings and dissipating it outside.


  1. What is the Difference Between Charle’s Law and Boyle’s Law?

Charle’s Law deals with the relationship between volume and temperature of a gas, while Boyle’s Law relates to the relationship between volume and pressure, with temperature held constant.

  1. Why is Kelvin Used in Gas Law Calculations?

Kelvin is used because it starts from absolute zero, ensuring non-negative values in gas law equations and providing a more accurate representation of temperature.

  1. Can Charle’s Law be Applied to All Gases Equally?

Charle’s Law is applicable to ideal gases, which perfectly follow the gas laws under all conditions. Real gases may not always follow these laws at extreme conditions.

  1. Who Discovered Charle’s Law?

Charle’s Law was formulated by Jacques Alexandre César Charles, a French physicist and inventor, in the late 18th century.

  1. Is Charle’s Law Only Applicable at Constant Pressure?

Yes, Charle’s Law is specifically applicable when the pressure of the gas remains constant.

  1. What are Some Practical Examples of Charle’s Law in Everyday Life?

Practical examples include hot air balloons, scuba diving, aerosol cans, and air conditioning systems.


In conclusion, Charle’s Law is a foundational concept in the study of gases and plays a vital role in numerous real-world applications.

Understanding how temperature affects gas volume has revolutionized various industries and enriched our lives in countless ways. From soaring high in hot air balloons to staying cool during scorching summers, Charle’s Law continues to shape the world around us.

So, the next time you witness a hot air balloon gently drifting in the sky or enjoy the refreshing breeze from an air conditioner, remember the profound impact of Charle’s Law, the gas law that transformed our understanding of nature’s behaviour.

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Gay-Lussac’s Law