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VI - EM - SCIENCE-HEAT-EVALUATION-QUESTION- ANSWERS
CLASS VI
EVALUATION
I. Choose the appropriate answer
1. When an object is heated, the molecules that make up the object
a. begin to move faster
b. lose energy
c. become heavier
d. become lighter
Ans: a. begin to move faster
2. The unit of heat is_______________
a. newton
b. joule
c. volt
d. Celsius
Ans: b. joule
3. One litre of water at 30° C is mixed with one litre of water at 50° C. The temperature of the mixture will be
a. 80oC
b. More than 50°C but less than 80° C
c. 20°C
d. around 40°C
Ans: d. around 40°C
4. An iron ball at 50°C is dropped in a mug containing water at 50°C. The heat will
a. flow from iron ball to water.
b. not flow from iron ball to water or from water to iron ball.
c. flow from water to iron ball.
d. increase the temperature of both.
Ans: b. not flow from iron ball to water or from water to iron ball.
II. Fill in the blanks:
1. Heat flows from a ____________ body to a ____________ body.
Ans: higher temperature, lower temperature
2. The hotness of the object is determined by its _______________.
Ans: temperature
3. The SI unit of temperature is ________.
Ans: kelvin
4. Solids________________ on heating and______________ on cooling.
Ans: expands, contract
5. Two bodies are said to be in the state of thermal______________ if there is no transfer of heat taking place.
Ans: equilibrium
III.True or False. If False, give the correct statement
1. Heat is a kind of energy that flows from a hot body to a cold body.
Ans: True
2. Steam is formed when heat is released from water.
Ans: True
3. Thermal expansion is always a nuisance.
Ans: False. All thermal expansions are not nuisance,some useful thermal expansion also there.
4. Borosilicate glass do not expand much on being heated.
Ans: True
5. The unit of heat and temperature are the same.
Ans: False.
Unit of heat is joule and the unit of temperature is kelvin
IV. Give reasons for the following
1. An ordinary glass bottle cracks when boiling water is poured into it, but a borosilicate glass bottle does not.
Ordinary glass is a poor conductor of heat. So, when boiling water is poured the surface of the glass in contact expands as per its coefficient of thermal expansion. But the outer layer of the glass remains to room temperature and does not expand. This difference in thermal expansion leads ordinary glass bottles to crack.
Borosilicate glasses have very low coefficients of thermal expansion, which makes them resistant and does not crack when hot water is poured into it.
2. The electric wire which sags in summer becomes straight in winter.
In summer, atmospheric temperature is high and due to which metal electric wires absorb heat and inturn expand their length. Hence, electric wires sag down.
In winter, atmospheric temperature is low, due to which metal wires cooled down and inturn contracts their length. Hence, electric wires become straight.
3. Rivet is heated before fixing in hole to join two metal plates.
Rivets were heated to glowing hot so that they were more malleable and easily deformed. Additionally, it offers a tight clamping and better leak-proof joints.
V. Match the following
Ans:
VI. Analogy
1. Heat : Joule :: Temperature : _____________
Ans: Kelvin
2. ice cube : 0°C :: Boiling water :_____________
Ans:100°C
3. Total Kinetic Energy of molecules: Heat :: Average Kinetic Energy : __________
Ans: Temperature
VII. Give very short answer
1. Make a list of electrical equipments at home which we get heat from.
Water heater, iron box, electric kettle etc.
2. What is temperature?
The measurement of warmness or coldness of a substance is known as its Temperature. SI unit of temperature is kelvin.
3. What is thermal expansion?
The expansion of a substance on heating is called, the thermal expansion of that substance.
4. What do you understand by thermal equilibrium?
Thermal equilibrium exists when two objects in thermal contact no longer affect each other's temperature.
VIII. Give short answer
1. What difference do you think heating the solid will make in their molecules ?
Molecules in objects are constantly vibrating or moving inside objects. We cannot see that movement with our naked eye. When we heat the object this vibration and movement of molecules increases and temperature of the object also increases.
2. Distinguish between heat and temperature.
IX. Answer in detail
1. Explain thermal expansion with suitable examples.
The expansion of a substance on heating is called, the thermal
expansion of that substance.
The expansion in length is called linear expansion.
The expansion in volume is called cubical expansion.
Examples:
1.Fitting the iron rim on the wooden wheel:
The iron ring is first heated to a higher temperature so that it expands in size and the hot ring is then easily slipped over to the rim of the wooden wheel. Cold water is now poured on the iron ring so that it contracts in size and holds the wooden wheel tightly
2. Rivetting:
Rivets are used to join two steel plates together.
Hot rivet is driven through the hole in the plates.
One end of the rivet is hammered to form a new rivet head.
When cooled, the rivet will contract and hold the two plates tightly together.
3. Electric wires:
Electric wires between electric posts contract on cold days and sag in summers. To avoid this problem, we leave wires slack so that they are free to change length.
