Given below are two statements. One is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Sharp glass edge becomes smooth on heating it up to its melting point.
Reason R: The viscosity of glass decreases on melting.
Choose the most appropriate answer from the options given below.
a)
Both A and R are true and R is the correct explanation of A.
b)
A is true, but R is false.
c)
A is false, but R is true.
d)
Both A and R are true, but R is not the correct explanation of A.
Correct answer is option 'D'. Can you explain this answer?

Question

Given below are two statements. One is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Sharp glass edge becomes smooth on heating it up to its melting point.
Reason R: The viscosity of glass decreases on melting.
Choose the most appropriate answer from the options given below.

a)
Both A and R are true and R is the correct explanation of A.
b)
A is true, but R is false.
c)
A is false, but R is true.
d)
Both A and R are true, but R is not the correct explanation of A.

Correct answer is option 'D'. Can you explain this answer?

Answer

Sharp glass edges are heated to make them smooth. On heating, glass melts and the surface of the liquid tends to take the rounded shape at the edges which has minimum surface area. This is called fire polishing of glass.
The viscosity of glass decreases on melting.
Both A and R are true, but R is not the correct explanation of A.

Answer

Assertion A: Sharp glass edge becomes smooth on heating it up to its melting point.
Reason R: The viscosity of glass decreases on melting.

Explanation:
When glass is heated to its melting point, it undergoes a phase change from a solid to a liquid state. This phase change is accompanied by an increase in temperature and a decrease in viscosity.

Viscosity of Glass:
Viscosity is a measure of a fluid's resistance to flow. In general, the higher the viscosity, the thicker the fluid and the slower it flows. The viscosity of a material depends on various factors, including temperature and pressure.

In the case of glass, as the temperature increases, the viscosity decreases. This is because the heat energy increases the kinetic energy of the glass molecules, causing them to move more freely and reducing the intermolecular forces that hold them in place.

Sharp Glass Edge:
When glass is melted, it becomes a molten liquid with lower viscosity. The sharp edges of the glass, which were present in the solid state, are now exposed to the molten glass. Due to the decreased viscosity, the molten glass can flow more easily and readily conform to the shape of the surrounding surface.

As a result, the sharp glass edge becomes smooth as it melts and flows, losing its distinct sharpness. This can be observed when heating glass edges, where the initially sharp edge gradually becomes smooth and rounded as it melts.

Conclusion:
Both Assertion A and Reason R are true. The melting of glass reduces its viscosity, allowing it to flow more easily and causing sharp glass edges to become smooth. The reason provided correctly explains the assertion. Hence, option D is the correct answer.

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