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Heat and Temperature
Heat and temperature are not the same thing, they in fact mean two different things;
* Temperature is related to how fast the atoms or molecules move or vibrate within the substance.
* Heat not only depends on the temperature of the substance but also depends on how many molecules are there in the object.
* Temperature measures the average kinetic energy of molecules. Heat measures the total Kinetic Energy of the molecules in the substance.
Activity 3: Take one litre water in a pan, and heat it on a stove. Calculate the time taken to start boiling. (i.e. the time taken to thermometer reading goes up to 100oC). Take five litre water in another pan and heat it on the same stove. Calculate the time taken by the water to start boiling.
In which pan the water starts to boil earlier?
__ One litre water
✔ Five litre water.
Both, however, show a temperature of 100oC at the boiling point. Five litre water takes more time to boil i.e. more heat is needed to boil the larger amount of water. So, five litre boiling water has more heat energy than one litre water.
Place an open can of lukewarm water in each pan. Observe their temperature to find out which can gets hotter.
In which can water shows quick rise in temperature?
✔ Can in One litre boiled water
__ Can in five litre boiled water.
You can see that, five litre water pan will raise the can of water to a higher temperature. Though, both pans of boiling water have the temperature of 100oC the five litre water can give off more heat energy than one litre water. Because it has more heat energy, and gives more energy to the water in the can.
Total heat is measured by calorie, the amount of heat needed to raise one gram of water by one degree centigrade.
* Which has more heat energy in each pair? Put ✓ mark.
Let Us Think
Pavithra is having tea while watching the pond near her house. Surely, tea is in higher temperature than the water in the pond. Now, a question is arising in Pavithra’s mind. Which one has more heat energy, a cup of tea or the water in the pond? What do you think? __________________________, __________________________________
Even though the temperature of the tea is higher than that of pond water, the volume of the water in pond is very high, hence the amount of molecules in the water in the pond is higher than the tea in the cup. So, pond has more heat energy than tea cup.
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