Heat

Question 1

What is the physical quantity ‘temperature’ and how is it measured?

Answer 1

Temperature is a measure of the degree of hotness or coldness of a body. It is measured using different units like degree Celsius (°C). degree Fahrenheit (°F). and Kelvin (K).

Question 2

What are the lower and upper fixed points on the temperature scales and what do they represent?

Answer 2

The lower fixed point on the temperature scales is where water freezes at level pressure. It is called ‘freezing point’. The upper fixed point is where water boils at level pressure. It is called ‘boiling point’.

Question 3

What are the freezing and boiling points of water on the Fahrenheit scale?

Answer 3

The freezing point of water on the Fahrenheit scale is 32 °F and the boiling point is 212 °F.

Question 4

What are the freezing and boiling points of water on the Kelvin scale?

Answer 4

The freezing point of water on the Kelvin scale is 273 K and the boiling point is 373 K.

Question 5

What is the SI unit of temperature and what is its symbol?

Answer 5

The SI unit of temperature is Kelvin and its symbol is K.

Question 6

What is the formula to convert from Celsius to Fahrenheit and vice versa?

Answer 6

Write On Paper

Question 7

What is the device used to measure the temperature of a body?

Answer 7

A device used to measure the temperature of a body is called a thermometer.

Question 8

What are the two common types of thermometers based on the type of liquid filled in them?

Answer 8

The two common types of thermometers based on the type of liquid filled in them are alcohol thermometer and mercury thermometer.

Question 9

Who invented the first mercury thermometer?

Answer 9

Gabriel Fahrenheit invented the first mercury thermometer.

Question 10

What are the advantages of mercury thermometers?

Answer 10

Mercury thermometers are advantageous in the following ways: . Mercury is a good conductor of heat and so quickly reaches the temperature of the surroundings. . It does not stick to the glass. . It has a high boiling point and a low freezing point. so it can measure a wide range of temperatures. . It has a visible silver color. which makes it easy to read.

Question 11

What are the disadvantages of mercury thermometers?

Answer 11

Mercury is a toxic substance.not suitable for measuring very high or very low temperatures not very accurate.

Question 12

What is the freezing point and boiling point of mercury?

Answer 12

The freezing point of mercury is approximately 39 °C and the boiling point is 357 °C.

Question 13

What are the advantages and disadvantages of using mercury as a thermometer liquid?

Answer 13

The advantages of using mercury as a thermometer liquid are: . It is a good conductor of heat and reacts quickly to temperature changes. . It does not stick to the glass. . It has a high boiling point and a low freezing point. so it can measure a wide range of temperatures. . It has a visible silver color. which makes it easy to read.

Question 14

What are the advantages of using alcohol as a thermometer liquid?

Answer 14

The advantages of using alcohol as a thermometer liquid are: . Alcohol is cheaper. easily available. and safe to use. . It has a low freezing point (115 °C) and therefore can be used to measure very low temperatures.

Question 15

What are the two types of mercury thermometers based on their usage?

Answer 15

The two types of mercury thermometers based on their usage are clinical and laboratory thermometers.

Question 16

What is the difference between clinical and laboratory thermometers?

Answer 16

Clinical thermometers are smaller in size as compared to laboratory thermometers. They have a temperature range marked on them for measuring human body temperature. Laboratory thermometers have a wider temperature range and are used for various scientific purposes.

Question 17

What is the normal human body temperature in Celsius and Fahrenheit?

Answer 17

The normal human body temperature in Celsius is 37 °C and in Fahrenheit is 98.6 °F.

Question 18

What are the disadvantages of using alcohol as a thermometer liquid?

Answer 18

The disadvantages of using alcohol as a thermometer liquid are: . Alcohol has a low boiling point (78 °C) and therefore cannot be used to measure high temperatures. . It does not react quickly to temperature changes. . As alcohol is colorless. it needs to be dyed before being used as a thermometer liquid.

Question 19

What is the device that rises and moves up to show the temperature against the printed scale?

Answer 19

The device that rises and moves up to show the temperature against the printed scale is mercury.

Question 20

What are the precautions to take while reading a clinical thermometer?

Answer 20

The precautions to take while reading a clinical thermometer are: . Wash the thermometer before and after use. . Handle the thermometer with care to prevent breakage. . Hold the thermometer horizontally (parallel to the floor) at eye level. . Make sure mercury level is below 35 °C before use. . Do not touch the bulb of the thermometer while reading it.

Question 21

What is the difference between a clinical thermometer and a laboratory thermometer in terms of their kink?

Answer 21

A clinical thermometer has a kink near the bulb to prevent the mercury from falling back. while a laboratory thermometer has no kink and the mercury falls back when removed from the source of heat.

Question 22

What is the typical range of a laboratory thermometer?

Answer 22

The typical range of a laboratory thermometer varies but is usually between 10 °C and 110 °C.

Question 23

What is a digital thermometer and how does it work?

Answer 23

A digital thermometer is a device that measures the human body temperature using a temperature sensor called a thermistor.

Question 24

What are the advantages of using a digital thermometer over a mercury or alcohol thermometer?

Answer 24

The advantages of using a digital thermometer over a mercury or alcohol thermometer are: . It does not contain mercury. which is toxic in nature. . It is lightweight and easy to carry. . It provides accurate and precise readings.

Question 25

What is heat and how is it transferred?

Answer 25

Heat is a transfer of energy between two bodies of different temperatures. Heat flows from the hotter body to the colder body until they have the same temperature.

Question 26

What are the three effects of heat?

Answer 26

The three effects of heat are: . It makes things hotter. . Heat can change the state of a substance. . Heat causes things to expand.

Question 27

What is an example of heat making things hotter?

Answer 27

An example of heat making things hotter is holding a metal spoon over a flame for a few seconds. The spoon will feel hot when touched.

Question 28

What is an example of heat changing the state of a substance?

Answer 28

An example of heat changing the state of a substance is putting ice cubes in a beaker. The ice cubes will melt and turn into liquid water.

Question 29

What is an example of heat causing things to expand?

Answer 29

An example of heat causing things to expand is fixing a small balloon on the mouth of an empty bottle and putting the bottle in a hot water tub. The balloon will expand as the air inside the bottle expands on heating.

Question 30

What is thermal expansion?

Answer 30

Thermal expansion is the increase in volume or size of a substance due to heating.

Question 31

What are some practical applications of thermal expansion?

Answer 31

Some practical applications of thermal expansion are: . A thick glass tumbler breaks when hot liquid is poured in it due to uneven expansion between the inner and outer surfaces. . Rail tracks have gaps left at places where two sections are joined to provide space for expansion during hot weather. . Cable wires between two poles are kept loose to prevent breakage during contraction in cold temperatures.

Question 32

What is the transfer of heat and how does it happen?

Answer 32

The transfer of heat is the movement of energy from a hotter body to a colder body until they have the same temperature. It happens when two bodies of different temperatures are brought in contact with each other.

Question 33

What is the process of heat transfer from a hot object to a cold object until they reach thermal equilibrium?

Answer 33

The process of heat transfer from a hot object to a cold object until they reach thermal equilibrium is called conduction.

Question 34

What is the difference between conduction and convection?

Answer 34

The difference between conduction and convection is that conduction is the transfer of heat without the actual displacement of particles. while convection is the transfer of heat by the movement of fluids (liquids or gases).

Question 35

What are conductors and insulators?

Answer 35

Conductors are substances that conduct heat. while insulators are substances that do not conduct heat or conduct very poorly.

Question 36

What is an example of a conductor and an insulator?

Answer 36

An example of a conductor is metal. which is used to make cooking vessels. An example of an insulator is wood. which is used to make handles for cooking vessels.

Question 37

How does heat transfer from the cooking vessels to the food?

Answer 37

Heat transfer from the cooking vessels to the food happens by conduction. The metal of the vessel gets hot when heated and transfers heat to the food. which helps the food to get cooked.

Question 38

What is convection and how does it occur?

Answer 38

Convection is a method of heat transfer in which there is actual movement of particles of the substance being heated. It occurs in fluids such as liquids and gases. when the hotter and less dense particles rise up and the colder and denser particles sink down. creating circular currents of heat.

Question 39

What are some applications of convection in everyday life?

Answer 39

Some applications of convection in everyday life are: . Ventilators located near the ceiling of rooms allow the hot air in the room to rise and move out of the ventilator. while fresh cool air from the window rushes in to take the place of the rising warm air. . Land and sea breezes occur near coastal areas as a result of convection currents set up in the air due to the difference in heating of the land and water surfaces.

Question 40

What are poor conductors of heat or insulators?

Answer 40

Poor conductors of heat or insulators are substances that do not conduct heat or conduct very poorly.

Question 41

What are some examples of insulators?

Answer 41

Some examples of insulators are wood. air. and water.

Question 42

Why are metal vessels provided with wooden handles?

Answer 42

Metal vessels are provided with wooden handles because wood does not conduct heat. so the handles do not get hot when the vessels are heated.

Question 43

What is radiation and how does it differ from conduction and convection?

Answer 43

Radiation is a method of heat transfer that does not require a medium to travel through. It differs from conduction and convection. which require a medium such as a solid or a fluid to transfer heat.

Question 44

How does the sun transfer heat to the earth?

Answer 44

The sun transfers heat to the earth by radiation. The heat from the sun travels through the empty space and reaches the earth. where some of it is absorbed and some of it is reflected.

Question 45

How does the color of an object affect its ability to absorb heat?

Answer 45

The color of an object affects its ability to absorb heat because different colors reflect and absorb different amounts of light and heat. Generally. darkcolored objects absorb more heat than lightcolored objects. because they reflect less light and heat.

Question 46

What are some practical implications of the color of an object on heat absorption?

Answer 46

Some practical implications of the color of an object on heat absorption are: . We prefer to wear darkcolored clothes in winter and lightcolored clothes in summer. because darkcolored clothes absorb more heat and keep us warm. while lightcolored clothes reflect more heat and keep us cool. . Solar panels are usually black or darkcolored. because they absorb more heat and convert it into electricity. . Roofs and walls of houses in hot regions are often painted white or lightcolored. because they reflect more heat and keep the interiors cool.

Question 47

What are sea breeze and land breeze?

Answer 47

Sea breeze and land breeze are phenomena of convection currents that occur near coastal areas due to the difference in heating of the land and water surfaces.

Question 48

How does sea breeze occur?

Answer 48

Sea breeze occurs during the day. when the land surface gets heated faster than the water in the sea. making the air above the land warmer and lighter. The warmer air over the land rises up and the cool air from the sea moves in to take its place. This creates a cool breeze from the sea to the land.

Question 49

How does land breeze occur?

Answer 49

Land breeze occurs during the night. when the land surface cools faster than the water in the sea. making the air above the sea warmer and lighter. The warmer air over the sea rises up and the cool air from the land moves in to take its place. This creates a cool breeze from the land to the sea.

Question 50

Why are air conditioners installed near the roof?

Answer 50

Air conditioners are installed near the roof because cool air is denser than warm air and tends to move down. while warm air near the surface of the room rises up. This sets up convection currents that cool the whole room effectively.

Question 51

What are some practical applications of radiation?

Answer 51

Some practical applications of radiation are: . Room heaters have mirrors behind the heating coils which reflect the heat radiated to the front. . Solar cookers have black metal sheets inside. which help in maximizing the heat absorption from the sun. . Cooking utensils which are blackened from outside absorb more heat and cooking can be done in less time. . The back of refrigerators are colored dull black. so that they are able to radiate heat in a better manner to the surroundings.