AIIMS 2003 Physics Heat Transfer Assertion Reason Question

To analyze the question regarding the assertion and reason provided, let's break down both statements and their relationship.

Assertion:

Temperatures near the sea coast are moderate.

This statement is true. Coastal areas typically experience milder temperatures compared to inland areas. This phenomenon occurs due to the large heat capacity of water, which helps in moderating temperature fluctuations. During the day, water absorbs heat, preventing the air temperature from rising too high. At night, the water releases heat slowly, preventing the air temperature from dropping too low.

Reason:

Water has a high thermal conductivity.

This statement is false. While water has a relatively high specific heat capacity (the amount of heat required to change the temperature of a unit mass of a substance by one degree Celsius), its thermal conductivity is not particularly high compared to metals. Thermal conductivity refers to the ability of a material to conduct heat, and water's thermal conductivity is moderate. For example, the thermal conductivity of water is about $0.6 \, \text{W/m·K}$, which is significantly lower than metals like copper or aluminum.

Conclusion on the Correct Answer:

Given the analysis:

• The assertion is true.
• The reason is false.

Therefore, the correct answer to the question is C) if assertion is true but reason is false.

Clarification of Other Options:

• A) if both assertion and reason are true and the reason is the correct explanation of the assertion: This option is incorrect because the reason is false.
• B) if both assertion and reason are true and the reason is not the correct explanation of the assertion: This option is also incorrect because the reason is false.
• D) if both assertion and reason are false statements: This option is incorrect since the assertion is true.

Relevant Concepts:

1. Specific Heat Capacity: Refers to the amount of heat required to change the temperature of a unit mass of a substance. Water has a high specific heat capacity, approximately $4.18 \, \text{J/g·°C}$, which helps in moderating temperature.

2. Thermal Conductivity: This is a property that indicates how well a material can conduct heat. For water, while it can absorb and release heat effectively due to its high specific heat, its thermal conductivity is moderate and not suitable as an explanation for temperature moderation near coastlines.

In summary, the assertion about moderate temperatures near the coast is accurate due to the high specific heat capacity of water, while the reason involving thermal conductivity is false, leading us to conclude that the correct option is C.