Heating it up : Heating it up Done by
Sitalakshmi N.S
Slide 2 : Remove a piece of toast from a toaster and pour hot soup into the bowl at the same time. Do they still remain hot after 5 minutes?
You will find that a few minutes later the soup will still be pleasantly warm, but the toast has cooled down.
Have you thought why it is so? Let’s find out
Slide 3 : 1 gram of water requires 1 calorie of heat energy to raise it’s temperature by 1 0C, but it takes only half of that energy to raise the temperature of 1 gram ethanol by that amount.
2 g of water requires more energy than 1 g of water to raise the temperature by 10C.
1 g of water requires more energy to raise its temperature by 100C than by 50C. Oh yeah! that’s why water takes a long time to cool down Heat a cup of water by a few degrees. The kettle feels a lot hotter than the water inside. Why?
Slide 4 : Amount of energy required to raise the temperature of unit mass of a substance by 1 degree celsius is called Specific heat capacity of a substance.
c=Q/mDT
SI unit of c is J/(kg K) Walking barefoot in sand in scorching sun is a different experience from walking in the evening. C- specific heat capacity
Q-heat energy
m- mass
DT- change in temperature
Slide 5 : Licking a silver spoon that’s been sitting in a very hot cup of coffee probably won’t burn your tongue. But a spoonful of the same hot coffee dropped on your tongue could leave a blister.
Slide 6 : Cooking Pot has body made of aluminium which has low c so that it can heat up quickly.
It has handle made of plastic which has high c to prevent easy conduction of heat.
It has a copper base with low c to heat up quickly.
Slide 7 : Water has high specific heat capacity and low cost. Hence water can be used as an effective cooling agent. Farmers fill their field with water in winter to prevent the damage of crops !!!
Slide 8 : Can you explain Land and sea breeze based on the concept you learnt?
Numerical : Numerical Calculate the heat energy required to raise the temperature of 2 kg of water from 100 celcius to 500 celcius. Specific heat capacity of water is 4200J/Kg/K.
Q = mcDT = 2 x 4200 x 40 = 336000 J
Summary : Summary Specific heat capacity of a substance depends on:
The amount of heat supplied
Mass of the substance
Rise in temperature
c=Q/mDT
Formative assessment : Formative assessment 1.Why do the metal parts of the car gets really hot while the plastic and other materials stay at more bearable temperature?
2.State the CGS unit of specific heat capacity
Research topic/Activity : Research topic/Activity Are there any disadvantages of using sea water rather than distilled or pure water to cool the nuclear reactors. Collect the newspaper articles if any related to this topic.
(Refer to recent nuclear catastrophe in Japan).
OR
2. Discuss the environmental impact of using sea water or river water for industrial cooling and the actions taken by EPA to regulate the same.