Heat & temperature
C. Short question
1. Define these terms; thermal energy, temperature and heat. Write their Sl units.
Ans: Thermal Energy:
The total kinetic energy and potential energy of all the particles
in a substance is called thermal energy. The SI unit of thermal energy is
Joul (J).
Temperature: The measure of average kinetic energy of particles of a body is
called temperature. The SI unit of temperature is Kelvin (K).
Heat:
Heat is a form of energy that flows from hotter body to colder body. SI unit of heat is joule (J).
2. Temperature of hot iron rod is 1000°C. Convert this temperature into kelvin and degree fahrenheit.
Ans: Given data.
Temeparture of hot iron rod (T) = 1000°C
Required: Convert into Kelvin =?
Convert into Fahrenhiet =?
Using the formula.
T(K)=T(c) + 273
Put values T(K) =1000+ 273
T (K) 1273 K For Fahrenheit using formula. =
T(F)= 1.8 T(c) + 32
T(F)= 1800+32 T(F) 1832 °F
T(F)= 1.8 (1000) + 32
T(F)=1832F
3. Why base of cooking utensils is made up of steel but handles are made up of plastic?
Ans: Cooking utensils are made up of
metals because metals are good conductor of heat and conduct heat fast and cooks the food easily.
While their handles are made up of plastic because plastic is bad conductor of heat so it cannot transfer heat to our hand. Therefore hand burning is avoided.
4. Il you put a dented ping pong ball in hat water, its dented part gets the proper shape. How doe it happen?
Ans: When we put a dented ping pong ball in hot water, its dented part gets a proper shape. It is due to the thermal expansion of the ball. When the ball absorb heat from hot water, its molecules expand and the dented part gets cracked shape.
5. How can gliders fly vary high without any engines! Give reason
Ans: Gliders can fly very high without any engines due to the convection current. During day air molecules gains energy and expand and thermal and fly very high. become lighter. This hot air rises straight up. Gliders find These thermal and fly very high.
6. Why most materials become less dense as their temperature is increased?
Ans: Most of materials become less dense when their temperature is increased because on heating the average kinetic energy of the molecules of material increase which lead to expansion. The molecules becomes lighter i.e. become less dense due to which it rises up.
7. Why exhaust fans are connected near the room ceiling?
Ans:Exhaust fans are connected near the room ceiling because when the air becomes hot it rises up to celling due to convection process. Then the exhaust fans pushes these hot air easily outside the room.
8. Briefly explain the expansion Joints use in the bridges.
Ans: Bridges have long span but it is divided into small sections will expansion joints between them due to these expansion Joints, bridge can expand and contract easily- during summer without any damage to bridge.
9. How false ceiling helps to keep room at lower temperature than outside during the summer?
Ans: False ceiling helps to keep room at lower temperature than outside during summer because in this process the air is trapped B/W the ceiling and roof. Air being good Insulator reduces the heat flow from roof to room.
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