Short Answer:

Boyle’s law states that for a given amount of gas at constant temperature, the pressure of a gas is inversely proportional to its volume. This means if the volume of a gas increases, its pressure decreases, and if the volume decreases, its pressure increases—as long as the temperature remains the same.

A simple example is a syringe: when you pull the plunger outward (increasing volume), the pressure inside drops. When you push the plunger in (decreasing volume), the pressure increases. This is how Boyle’s law works in real life.

Detailed Explanation:

Boyle’s law with an example

Boyle’s law is one of the basic gas laws in thermodynamics and explains how the pressure and volume of a gas are related, keeping temperature and number of gas particles constant. It was discovered by Robert Boyle in the 17th century. This law helps us understand how gases behave under pressure and is important in designing engines, compressors, and many other mechanical systems.

Statement of Boyle’s Law

“The pressure of a fixed amount of gas is inversely proportional to its volume at constant temperature.”

Mathematically, Boyle’s law is expressed as:

P × V = constant

Or,

P₁V₁ = P₂V₂

Where:

P₁ and V₁ are the initial pressure and volume.
P₂ and V₂ are the final pressure and volume.
Temperature and the number of gas molecules remain constant.

This equation tells us that if the volume increases, the pressure decreases and if the volume decreases, the pressure increases.

Explanation with Real-Life Example

Syringe Example:

Let’s take the example of a medical syringe:

When you pull the plunger back, the volume inside increases.
As volume increases, pressure inside the syringe drops.
This causes liquid or air to be sucked into the syringe.

Now, when you push the plunger in:

The volume decreases.
The pressure inside increases.
This pushes the fluid or air out of the syringe.

This is a practical and everyday application of Boyle’s law.

Another Example: Balloon in a Vacuum Chamber

If you place a balloon in a vacuum chamber and start removing air (reducing external pressure):

The pressure outside the balloon decreases.
As a result, the air inside the balloon pushes outward more strongly.
The balloon expands in volume.

Again, this shows the inverse relationship between pressure and volume.

Graphical Representation

On a P-V graph (Pressure vs. Volume), Boyle’s law forms a hyperbola.
As pressure increases, volume decreases, and vice versa.
The product P × V remains constant for each point on the curve.

Applications of Boyle’s Law

Pneumatic tools – Pressure and volume control air-powered machines.
Air compressors – Compress air by reducing its volume and increasing pressure.
Lungs and Breathing – Inhalation increases lung volume, decreasing pressure and allowing air to enter.
SCUBA Diving – Understanding pressure changes under water helps divers avoid injuries.
Syringes and Pumps – Basic medical tools that rely on pressure-volume relationships.

Limitations of Boyle’s Law

Only applies when temperature is constant.
Does not hold at very high pressures or very low temperatures, where gas molecules start to interact or condense.
Assumes gas behaves as an ideal gas, which may not be true in extreme conditions.

Despite these limitations, Boyle’s law works very well under normal laboratory and practical conditions.

Conclusion

Boyle’s law explains how the pressure of a gas changes when its volume changes, provided the temperature stays constant. It shows that pressure and volume are inversely proportional, which means that when one increases, the other decreases. This law is used in many daily-life tools and machines, such as syringes, pumps, and air compressors. Understanding Boyle’s law helps in analyzing gas behavior and improving the design of systems that deal with gases.