AIIMS 2007 Physics Viscosity Assertion Reason Question

Explanation

To analyze the given question, we need to evaluate the Assertion and the Reason provided:

Assertion: Machine parts are jammed in winter.
Reason: The viscosity of lubricant used in machine parts increases at low temperatures.

Step 1: Evaluating the Assertion

The assertion states that machine parts are jammed in winter. This is a common observation in many mechanical systems, especially those that operate outdoors or are not adequately insulated. During winter, temperatures drop significantly, and various factors such as the contraction of materials and the increase in friction can lead to jamming.

Step 2: Evaluating the Reason

The reason provided states that the viscosity of lubricants increases at low temperatures. Viscosity is a measure of a fluid's resistance to flow. For most lubricants, particularly oils, viscosity does indeed increase as the temperature decreases. This means that when the temperature drops, the lubricant becomes thicker, leading to reduced flow and, consequently, higher friction between moving parts.

Conclusion on the Correct Answer

Both the assertion and the reason are true. The reason accurately explains why machine parts may jam in winter due to the increased viscosity of the lubricants used. As a lubricant becomes more viscous, it cannot flow as easily between moving parts, leading to increased friction and potential jamming.

Thus, the correct answer is: A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

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Why Other Options are Incorrect

• B) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

  • This option is incorrect because the reason provided does effectively explain the assertion. The increase in viscosity directly contributes to the jamming of machine parts.

• C) Assertion is true but Reason is false.

  • This option is incorrect because both the assertion and the reason are true. The reason’s statement about viscosity is scientifically accurate.

• D) Both Assertion and Reason are false.

  • This option is incorrect as both statements are true. The assertion about machine parts jamming in winter is a recognized phenomenon, and the reason regarding lubricant viscosity is accurate.

Relevant Concepts

1. Viscosity: Defined as the measure of a fluid's resistance to deform under shear stress. The relationship between temperature and viscosity can often be described using empirical formulas such as the Arrhenius equation for certain fluids.

2. Effect of Temperature on Viscosity:

   • For a Newtonian fluid, viscosity can be approximated by: $\eta(T) = k \cdot e^{\frac{E_a}{RT}}$ where:
   • $\eta(T)$ is the viscosity at temperature $T$,
   • $k$ is a constant,
   • $E_a$ is the activation energy for flow,
   • $R$ is the universal gas constant.

   As temperature decreases ($T$ decreases), the viscosity $\eta(T)$ increases, confirming the reason provided.

In summary, both the assertion and the reason are correct, and the reason provides a valid explanation for the assertion, reinforcing the answer as A.