Samacheer Kalvi 6th Science Term 2 Unit 1 Book Back Question and Answers:
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TN State Board Class 6th Science Subject Term 2 Unit 1 one mark and two mark solutions guide PDF available below.
6th Science – Term 2
Unit 1: Heat
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
Answer: (a) begin to move faster
2. The unit of heat is
Answer: (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
(b) More than 50°C but less than 80°C
(d) around 40°C
Answer: (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.
Answer: (b) not flow from iron ball to water or from water to iron ball
II. Fill up the blanks:
- Heat flows from a ______ body to a ______ body.
- The hotness of the object is determined by its ______
- The SI unit of temperature is ______
- Solids on heating and ______ on cooling.
- Two bodies are said to be in the state of thermal ______ if there is no transfer of heat taking place.
- higher temperature, lower temperature
- expand, contract
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.
2. Steam is formed when heat is released from water.
Answer: False. Ice is formed when heat is released from water.
3. Thermal expansion is always a nuisance.
Answer: False. Thermal expansion is always beneficial.
4. Borosilicate glass does not expand much upon being heated.
5. The unit of heat and temperature are the same.
Answer: False. The units of heat and temperature are different
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.
The borosilicate glass is pyrex glass. They do not expand much on being heated and therefore they do not crack.
2. The electric wire which sag in summer become straight in winter.
In summer the electric wire is expanded by high temperature. So it sags in summer. In winter die electric wire is contracted by low temperatures. Hence it becomes straight in winter.
3. Rivet is heated before fixing in the hole to join two metal plates.
In order to make the other end of the rivet to form a new “rivet-head” by hammering, the rivet is heated. It becomes malleable when the rivet is in red-hot condition.
V. Match the following:
|3. Thermal Equilibrium||kelvin|
|4. Ice cube||No heat flow|
|5. Boiling water||joule|
|3. Thermal, Equilibrium||No heat flow|
|4. Ice cube||0°C|
|5. Boiling water||100°C|
1. Heat: Joule :: Temperature : _______
2. Ice cube : 0°C :: Boiling water : _______
3. Total Kinetic Energy of molecules: Heat:: Average Kinetic Energy: _______
VII. Give a Very Short Answer:
1. Make a list of electrical equipment at home from which we get heat.
The water heater, iron box, electric cattle, etc.,
2. What is the temperature?
- The measurement of the warmness or coldness of a substance is known as temperature.
- SI unit is Kelvin.
- Other units: Celsius, Fahrenheit
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 (or) Both the objects are in the same temperature they are in thermal equilibrium.
VIII. Give a Short Answer:
1. What difference do you think heating the solid will make in their molecules?
Heat expands solids. The molecules in the solid move faster, spread apart, and occupy more space.
2. Distinguish between heat and temperature.
|1.||Heat not only depends on the temperature of the substance but also depends on how many molecules are there in the object.||Temperature is related to how fast the atoms or molecules move or vibrate within the substance|
|2.||Heat measures the total Kinetic Energy of the molecules in the substance.||Temperature measures the average kinetic energy of molecules.|
|3.||SI Unit: Joule||SI Unit: Kelvin|
|4.||Unit: Joules, Calories||Unit: Fahrenheit, Celsius, Kelvin|
|5.||It has the ability to do work||It can be used to measure the degree of heat|
IX. Answer in detail:
1. Explain thermal expansion with suitable examples.
The expansion of a substance on heating is called, the thermal expansion of those substances.
- Gaps are left in between rails while laying on a railway track. The reason is during summer thermal expansion takes place.
- Gaps are left in between two joints of a concrete bridge because of thermal expansion.
- Electric wires between electric posts contract on cold days and sag in summer.
- By fitting the iron rim on the wooden wheel they will heat the iron rim expansion takes place. They will fit with the wheel when the rim is cold, it will not slip.
- Riveting: To join two steel plates together, a hot rivet is driven through the hole of the plates.
One end of the rivet is hammered to form new heat when cooled the rivet will contract and hold tightly.
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