Question

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: The conical shell of a ball mill is operated at a speed slightly higher than the critical speed.
Reason R: Critical speed of a ball is that rotational speed at which centrifuging occurs.
In light of the above statements, choose the correct answer from the options given below:

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true but R is NOT the correct explanation of A
• C. A is true but R is false
• D. A is false but R is true

Hint:

To ensure effective grinding, the operating speed of a ball mill must always be below its critical speed:
\[ N_{\text{operating}} \approx (0.65 \text{ to } 0.80) \cdot N_{\text{critical}} \]
At or above critical speed, centrifuging prevents any grinding action.

Answer 1

The Correct Option is D