Heat
Tamil Nadu Board · Class 9 · Science
Most important questions from Heat for Tamil Nadu Board Class 9 Science board exam 2026. MCQs, short answer, and long answer questions with marks.
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Sample Questions
During daytime, a cool breeze blows from the sea towards the land. What is the reason for this sea breeze?
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Land heats up faster, hot air rises, and cool sea air moves in to replace it
Step 1: During the day, the sun heats the land faster than the sea. Step 2: The hot air above the land becomes less dense and rises upward. Step 3: This creates a low-pressure area above the land. Step 4: Cool air from over the sea (which is at higher pressure) moves towards the land to fill this low-pressure area. Step 5: This movement of cool air from sea to land is called sea breeze. This is a real-life example of convection in nature.
Which of the following statements about radiation is CORRECT?
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Radiation can travel through vacuum as electromagnetic waves
Step 1: Radiation is the transfer of heat in the form of electromagnetic waves. Step 2: Electromagnetic waves do not need any medium to travel — they can pass through a vacuum. Step 3: This is how heat from the Sun reaches the Earth, even through the vacuum of space. Step 4: Radiation travels at the speed of light, which is much faster than sound. Step 5: Like all heat transfer, radiation flows from hotter to cooler objects. This makes radiation unique compared to conduction and convection, which both need matter.
What is the temperature of 37°C (normal human body temperature) converted to Kelvin?
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310.15 K
Step 1: The formula to convert Celsius to Kelvin is: K = C + 273.15. Step 2: Substitute the given value: K = 37 + 273.15. Step 3: K = 310.15 K. Step 4: 373.15 K is the boiling point of water (100°C), not 37°C. Step 5: Always remember that Kelvin temperature is always higher than the Celsius temperature by 273.15 units. This formula is very important and is used in many scientific calculations.
Calculate the heat energy required to raise the temperature of 1 kg of water from 20°C to 70°C. (Specific heat capacity of water = 4200 J/kg·K). Which of the following is the correct answer?
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210,000 J
Step 1: Use the formula Q = m × C × ΔT. Step 2: Identify values: m = 1 kg, C = 4200 J/kg·K, ΔT = 70 - 20 = 50°C (or 50 K). Step 3: Substitute: Q = 1 × 4200 × 50. Step 4: Q = 210,000 J or 2.1 × 10⁵ J. Option 84,000 J is wrong (uses ΔT = 20 incorrectly). Option 4,200 J is only the heat for 1°C rise. Option 294,000 J uses ΔT = 70 without subtracting the initial temperature.
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