Question

Given below are two statements one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): As spun polyester fibre gives almost zero value of birefringence. Reason (R): As spun polyester fibre is highly oriented. In the light of the above statements, choose the most appropriate answer from the options given below:

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Drawing = High Birefringence. As-spun = Low/Zero Birefringence. They are inversely related to the stage of production.

Answer 1

The Correct Option is C

Concept: Birefringence is a direct numerical indicator of molecular orientation. If molecules are randomly arranged (isotropic), birefringence is zero.

Step 1: Analyzing Assertion (A).
"As spun" fibers are those that have just been extruded and solidified but have not yet been "drawn" (stretched). In this state, the polymer chains are still in a largely disordered, random state. Consequently, the difference in refractive index is negligible, resulting in almost zero birefringence. Thus, (A) is correct.

Step 2: Analyzing Reason (R).
Since as-spun fibers have zero birefringence precisely because they are not yet aligned, the statement that they are "highly oriented" is factually incorrect. High orientation only occurs after the drawing process.