Pascal’s Law


Pascal’s Law – Class 11 Physics Notes

In this post, we will understand Pascal’s Law with a clear definition, a simple diagram,
mathematical formula, and a short numerical example. Video explanation is also given.

Class 11 Physics
Mechanical Properties of Fluids
Pressure in Fluids
JEE / NEET / Boards
📄 Download Pascal’s Law Notes (PDF)
▶ Watch Pascal’s Law Video

📌 Table of Contents

  1. Introduction
  2. Definition of Pascal’s Law
  3. Diagram to Explain Pascal’s Law
  4. Mathematical Formula
  5. Applications of Pascal’s Law
  6. Numerical Example
  7. Video Explanation
  8. FAQ

🔍 Introduction

When we apply pressure at one point in a fluid (like oil in a hydraulic system), we observe that
the effect of this pressure is felt everywhere in the fluid. This important behaviour of fluids
is explained by Pascal’s Law.

Pascal’s Law is very useful in designing machines like hydraulic lifts, hydraulic brakes,
hydraulic jacks etc. It is a key topic in the chapter
Mechanical Properties of Fluids for Class 11.

🧾 Definition of Pascal’s Law

Pascal’s Law:


When an external pressure is applied to a confined fluid, the pressure is transmitted
undiminished and equally in all directions throughout the fluid and to the walls of the container.

In simple words:
If you press a fluid inside a closed container at one place, the same pressure appears at
every other place in that fluid.

📊 Diagram to Explain Pascal’s Law (Hydraulic Lift)

A common device to show Pascal’s Law is a hydraulic lift. It has two pistons of different areas
connected by a fluid (usually oil).

A1, F1

Small piston
Force F1 on area A1

A2, F2

Large piston
Force F2 on area A2

Fig: Hydraulic lift – pressure applied at the small piston is transmitted equally to the fluid
and produces a larger force at the bigger piston.

Because of Pascal’s Law, the pressure in the fluid is the same at both pistons, so:

Pressure at small piston = Pressure at large piston

⇒   F1 / A1 = F2 / A2

📐 Mathematical Formula of Pascal’s Law

The basic formula for pressure is:

P = F / A
  • P = Pressure (in Pascal, Pa)
  • F = Force (in Newton, N)
  • A = Area (in m²)

In hydraulic systems, Pascal’s Law gives the relation:

F1 / A1 = F2 / A2

This means a small force acting on a small area can produce a large force on a large area.
This is called force multiplication.

⚙ Applications of Pascal’s Law

  • Hydraulic Lift: Used in car service stations to lift vehicles.
  • Hydraulic Jack: Used to lift heavy loads like cars for tyre change.
  • Hydraulic Press: Used in industries to compress, mold, or shape materials.
  • Hydraulic Brakes: Used in cars and bikes for uniform braking.
  • Medical Instruments: Blood pressure instruments and syringes work on similar principle.

🧮 Numerical Example on Pascal’s Law

Example: A force of 50 N is applied on a small piston of area 5 cm² in a hydraulic lift.
Calculate the pressure produced in the fluid.

Step 1 – Convert area to m²:

5 cm² = 5 × 10⁻⁴ m²

Step 2 – Use P = F / A

P = 50 N / (5 × 10⁻⁴ m²)

P = 1,00,000 Pa = 100 kPa

Answer: Pressure produced in the fluid is 100 kPa.

▶ Pascal’s Law Video Explanation

Watch this video to understand Pascal’s Law with animation and examples:

🔁 You can pause, replay and use this video in your classroom or tuition for explaining
Pascal’s Law visually.

❓ Frequently Asked Questions

Q1. Who gave Pascal’s Law?

Answer: Pascal’s Law was given by the French scientist Blaise Pascal.

Q2. Why is Pascal’s Law important?

It helps us design machines that can lift very heavy loads using small forces. It is the
working principle behind all hydraulic machines.

Q3. Does Pascal’s Law apply to gases also?

Pascal’s Law mainly applies to incompressible fluids (like liquids). Gases are compressible,
so their behaviour is more complicated.