Science · X-Factor Notes
Heat and Thermodynamics revision notes for UPPCS Prelims.
High-Yield Revision| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Heat | Defined as energy which transfers from one system to another as a result of their difference in temperature. The SI unit is Joule. | |
| Temperature | A thermal state of an object that expresses the direction of flow of heat. Heat always transfers from a substance of higher temperature to one of lower temperature. | |
| Temperature Measurement | Pyrometer (Radiation thermometer) is a device used to measure extremely high temperatures, often above 15000C. | U.P. P.C.S. (Mains) 2016, U.P. P.C.S. (Pre) 2016, UPPCS (Pre) 2009 |
| Absolute Zero Temperature | The theoretically lowest possible temperature (0 K or -273.150C) where atoms transmit no thermal energy,minimum internal energy. | |
| Energy in Steam vs. Water | Steam at 1000C causes more severe burns than boiling water at 1000C because steam possesses latent heat of vaporization (approximately 540 cal/gm more heat). | U.P. P.C.S. (Pre) 1993 |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Modes of Heat Transfer | Convection occurs through the actual movement of matter and is possible only in gases and liquids (fluids). Radiation does not require a medium. | U.P. R.O./A.R.O. (Mains) 2017 |
| Thermos Flask | A liquid remains hot or cold for a long time due to the vacuum gap between the walls, preventing heat loss or gain by conduction, convection, and radiation. | UPPCS (Pre) 2019 |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Thermostat in Refrigerator | The thermostat automatically regulates the temperature of a system. The safest temperature for keeping food fresh is 40C (35F to 40F). | UPPCS (Pre) 2007 |
| Cooling Mechanism | A desert room cooler works on the principle of evaporative cooling. The rate of evaporation of sweat, which causes cooling, is increased by a fan. | UPPCS (Pre) 2005 |
| Drying Conditions |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Pressure Cooker | Food cooks faster because the increased pressure inside the cooker raises the boiling point of water. The cooking temperature depends mainly on the area of the hole in the lid and the weight of the lid. | U.P. Lower Sub. (Pre) 2002, UPPCS (Pre) 2015, UPPCS (Pre) 1995 |
| Boiling/ Freezing Point Modification | Adding common salt (impurities) to water will increase the boiling point and decrease the freezing point. | UPPCS (Mains) 2006 |
| Water Density/Volume Anomaly |
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| When water is heated from 00C to 100C, its volume first decreases till 40C and then increases. Density is maximum at 40C. |
| Melting Ice in Water | When a piece of ice floating in a glass of water melts, the water level will remain the same. |
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| Water Freezing Expansion | When water freezes in a bottle, the bottle breaks because water expands upon freezing. |
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| Wet clothes dry earliest under conditions of minimum humidity and maximum temperature. |
| UPPCS (Pre) 2008 |
| Cooling by Ice | Ice takes latent heat from the surrounding drink to melt, resulting in the cooling of the drink. | U.P. Lower Sub. (Pre) 2009 |
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| Heat Conduction in Solids | Metals like copper are excellent heat conductors. A copper piece feels hotter than a glass piece (poor conductor) even if heated to the same temperature, as copper transfers heat more effectively to the hand. |
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| Body Temperature Regulation | The most important function of perspiration is to regulate body temperature. |
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| Temperature Scales Conversion | The normal human body temperature is approximately 36.90C | UPPCS (Pre) 2024, UPPCS (Pre) (Re. Exam) 2015 |
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| Newton’s Law of Cooling | The rate of cooling is directly proportional to the temperature difference between the body and the surroundings. A body cools slower when the temperature difference is smaller. | U.P. P.C.S. (Mains) 2017 |
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| Clothing Preference | Light colours are preferred in summer because they are poor absorbers of heat (good reflectors). | U.P. R.O./A.R.O. (Pre) 2016 |
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