Q.19 In the technique called centrifugation, the centrifugal field (G) is calculated as:
- G = ω × r2
- G = ω2 × r
- G = ω2 × r2
- G = ω × r
Introduction
Centrifugation is an important laboratory technique used to separate particles based on density, size, and mass.
When a sample rotates at high speed, it experiences a centrifugal field (G) that pushes particles outward.
This field depends on angular velocity (ω) and radial distance (r).
Understanding the correct formula is very important for exams like CSIR-NET, GATE, and NEET.
Concept of Centrifugal Field
From circular motion physics, centrifugal acceleration is given by:
Where:
ω = angular velocity (rad/s)
r = distance from center
a or G = centrifugal acceleration
✔ Correct Answer: Option B (G = ω2 × r)
Explanation of Each Option
Option A: G = ω × r2
Incorrect because angular velocity is not squared and the radius is unnecessarily squared.
Units become dimensionally incorrect.
Option B: G = ω2 × r
Correct formula derived from circular motion. It matches the physical law of centrifugal acceleration.
Option C: G = ω2 × r2
Incorrect because squaring the radius exaggerates the force and does not match any standard equation.
Option D: G = ω × r
Incorrect since angular velocity must be squared to represent acceleration. Hence dimensionally invalid.
Practical Laboratory Application
In real centrifuges, Relative Centrifugal Force (RCF) is calculated using:
This formula is derived from the same principle: G = ω2 r.
Always remember → Force is proportional to the square of speed (ω2).
If ω is not squared, the answer is wrong.
