Heat

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Q1. The transfer of heat by the movement of a fluid is called ______.
Convection is the transfer of heat by the actual movement of a fluid (liquid or gas). When a fluid is heated, it expands, becomes less dense, and rises, while cooler, denser fluid sinks, creating convection currents. Conduction occurs in solids, radiation does not need a medium, and insulation prevents heat transfer.

Q2. In which mode of heat transfer does the medium itself move from one place to another?
In convection, the medium itself moves from one place to another. The heated fluid rises, and cooler fluid sinks, creating convection currents. In conduction, particles vibrate but do not move as a bulk. Radiation does not require a medium, and expansion is a result of heating, not a mode of transfer.

Q3. Convection currents in water can be demonstrated by heating water containing ______.
Convection currents in water can be demonstrated by adding a few drops of ink or potassium permanganate crystals. The coloured water shows the movement of currents as the heated water rises and cooler water sinks. Sand, sugar, and salt would not effectively show the movement.

Q4. When water is heated, the warmer part of the water ______.
When water is heated, it expands, becomes less dense, and rises. The cooler, denser water sinks to take its place, setting up convection currents. This is why warmer water is found at the top of a heated container.

Q5. The circulating movement of liquid or gas due to uneven heating is called a ______.
The circulating movement of liquid or gas due to uneven heating is called a convection current. Heated fluid rises and cooler fluid sinks, creating a circular flow. Wind currents and ocean currents are specific types of convection currents, and electric current is different.

Q6. A convection tube filled with water demonstrates convection by showing that ______.
A convection tube demonstrates that heated water rises and cool water sinks. This movement creates convection currents in the water. It shows that convection involves the bulk movement of the fluid, not just conduction.

Q7. The best evidence of convection in air is provided by ______.
Sea breezes and land breezes are the best evidence of convection in air. They are caused by the uneven heating of land and sea, creating convection currents. A fan blows air, a hair dryer produces forced convection, and smoke shows movement but is not the best evidence.

Q8. The process of convection in air is responsible for the formation of ______.
Convection in air is responsible for the formation of winds and breezes. Uneven heating of the Earth’s surface creates convection currents in the atmosphere, which we experience as wind. Rainbows are optical phenomena, earthquakes are geological, and tides are caused by the moon’s gravity.

Q9. In a convection current, warm air rises because it is ______.
In a convection current, warm air rises because it is less dense than the surrounding cooler air. When air is heated, it expands, and its density decreases, causing it to rise. Denser air sinks.

Q10. When air is heated, it ______.
When air is heated, it expands, becomes less dense, and rises. This is the principle behind convection currents. Cooler air is denser and sinks. Heating causes expansion, not contraction.

Q11. Sea breeze blows during the ______.
Sea breeze blows during the daytime. During the day, the land heats up faster than the sea, creating a pressure difference. The air over the land rises, and cooler air from the sea moves in to take its place, blowing from the sea to the land.

Q12. Land breeze blows during the ______.
Land breeze blows during the night-time. At night, the land cools faster than the sea, creating a pressure difference. The air over the sea rises, and cooler air from the land moves out to the sea, blowing from land to sea.

Q13. During the day, the air over the land becomes ______.
During the day, the air over the land becomes hotter and lighter because the land absorbs heat faster and heats the air above it. The heated air expands, becomes less dense, and rises. This creates a low-pressure area over the land.

Q14. During a sea breeze, the wind blows from ______.
During a sea breeze, the wind blows from the sea to the land. The sea is cooler than the land during the day, so the cooler, denser air from the sea moves towards the land to replace the rising warm air over the land.

Q15. During a land breeze, the wind blows from ______.
During a land breeze, the wind blows from the land to the sea. At night, the land cools faster than the sea, so the cooler, denser air from the land moves towards the sea to replace the rising warm air over the sea.

Q16. The main reason for the formation of sea and land breezes is ______.
Sea and land breezes are formed due to the difference in the heating and cooling rates of land and water. Land heats up and cools down faster than water. This creates temperature differences that lead to convection currents in the air.

Q17. Which of the following is a good conductor of heat?
Iron is a metal and a good conductor of heat. Wood, plastic, and cork are poor conductors (insulators). Metals have free electrons that transfer heat quickly, making them good conductors.

Q18. Which of the following is a poor conductor of heat (an insulator)?
Plastic is a poor conductor of heat (an insulator). Copper, aluminium, and steel are all metals and good conductors of heat. Insulators are used to prevent heat transfer, such as in handles of utensils.

Q19. The materials which allow heat to pass through them easily are called ______.
Materials that allow heat to pass through them easily are called conductors. Metals like copper, iron, and aluminium are good conductors. Insulators do not allow heat to pass through easily. Radiation and convection are modes of heat transfer, not materials.

Q20. The materials which do not allow heat to pass through them easily are called ______.
Materials that do not allow heat to pass through them easily are called insulators. Examples include wood, plastic, and rubber. Conductors allow heat to pass through, transparent materials allow light, and radiators are devices that emit heat.

Q21. The phenomenon by which heat is transferred from the sun to the earth is called ______.
Heat from the sun reaches the earth by radiation because there is a vacuum in space, and conduction and convection require a medium. Radiation is the transfer of heat through electromagnetic waves and does not need a medium.

Q22. Dark-coloured surfaces are ______ absorbers of heat.
Dark-coloured surfaces are good absorbers of heat. This is why dark clothes make you feel warm in the sun. Light-coloured surfaces reflect heat, making them poor absorbers.

Q23. Light-coloured surfaces are ______ reflectors of heat.
Light-coloured surfaces are good reflectors of heat. This is why we wear light-coloured clothes in summer to stay cool. Dark surfaces are poor reflectors and good absorbers of heat.

Q24. Which type of surface is the best emitter of heat radiation?
Dull black surfaces are the best emitters of heat radiation. They also absorb heat well. Shiny and polished surfaces reflect heat and are poor emitters. Transparent surfaces allow radiation to pass through but are not good emitters.

Q25. The degree of hotness or coldness of a body is called its ______.
Temperature is the degree of hotness or coldness of a body. It is a measure of the average kinetic energy of the particles in a substance. Heat is a form of energy, mass is the amount of matter, and volume is the space occupied.

Q26. The device used to measure temperature is called a ______.
A thermometer is used to measure temperature. A barometer measures atmospheric pressure, a hydrometer measures liquid density, and a voltmeter measures voltage. The thermometer is the correct instrument for temperature.

Q27. The Celsius scale is also known as the ______ scale.
The Celsius scale is also known as the centigrade scale because it has 100 degrees between the freezing and boiling points of water. Fahrenheit and Kelvin are different scales, and absolute is another name for the Kelvin scale.

Q28. On the Celsius scale, the lower fixed point (freezing point of water) is ______.
On the Celsius scale, the lower fixed point (freezing point of water) is 0°C. The upper fixed point (boiling point) is 100°C. 32°F is the freezing point on the Fahrenheit scale, and -273°C is absolute zero on the Kelvin scale.

Q29. On the Celsius scale, the upper fixed point (boiling point of water) is ______.
On the Celsius scale, the upper fixed point (boiling point of water) is 100°C. The lower fixed point is 0°C. 212°F is the boiling point on the Fahrenheit scale, and 32°F is the freezing point on the Fahrenheit scale.

Q30. The temperature of a healthy human body is about ______.
The normal temperature of a healthy human body is about 37°C. This is equivalent to 98.6°F. 0°C is the freezing point of water, 50°C is too high for body temperature, and 100°C is the boiling point of water.

Q31. Which of the following is an example of a good insulator?
Woollen clothes are good insulators because they trap air and prevent heat loss. Iron, copper, and aluminium are good conductors of heat. Insulators are used to keep us warm by preventing heat transfer.

Q32. The kink in a clinical thermometer prevents the ______ from falling back on its own.
The kink (constriction) in a clinical thermometer prevents the mercury from falling back on its own after a reading is taken. This allows the user to read the temperature even after the thermometer is removed from the mouth.

Q33. A laboratory thermometer differs from a clinical thermometer because it lacks a ______.
A laboratory thermometer does not have a kink (constriction). The kink is present only in clinical thermometers to hold the mercury reading. Laboratory thermometers have a bulb, a scale, and contain mercury or alcohol.

Q34. Which of the following is a liquid crystal thermometer used for?
Liquid crystal thermometers are often used as forehead strips to measure body temperature. They change colour with temperature. They are not used for high temperatures, room temperature, or boiling water.

Q35. The range of a laboratory thermometer is generally ______.
The range of a typical laboratory thermometer is -10°C to 110°C, making it suitable for a wide variety of experiments. 35°C to 42°C is the range of a clinical thermometer, and the other ranges are too narrow.

Q36. In which of the following is heat transferred by convection?
Boiling water in a pan involves convection currents. The heated water rises and cooler water sinks. A metal rod getting hot and a spoon in tea are examples of conduction, and sun’s rays reaching Earth is radiation.

Q37. The air conditioner in a room is usually fitted near the ceiling because it ______.
An air conditioner is fitted near the ceiling because cool air is denser and sinks, setting up convection currents that cool the entire room. This is an application of convection. Appearance and electricity savings are not the primary reasons.

Q38. Room heaters are usually placed on the floor because ______.
Room heaters are placed on the floor because hot air rises, setting up convection currents that warm the entire room. This is an application of convection. Safety and power points are not the primary reasons.

Q39. During a sea breeze, the air above the sea is ______ than the air above the land.
During a sea breeze, the air above the sea is cooler than the air above the land. This is because land heats up faster than water during the day. The cooler air from the sea moves towards the land, creating a sea breeze.

Q40. The specific heat capacity of land is ______ than that of water.
The specific heat capacity of land is lower than that of water. This means land heats up and cools down faster than water. This difference is the reason for the formation of sea and land breezes.

Q41. The process in which heat is transferred without any medium is called ______.
Radiation is the process of heat transfer that does not require any medium. Heat from the sun reaches the earth through radiation. Conduction and convection require a medium, and a conductor is a material that allows heat to pass.

Q42. In a thermos flask, the vacuum between the two walls prevents heat loss by ______.
The vacuum between the two walls of a thermos flask prevents heat loss by conduction and convection because there is no medium for heat to travel through. Radiation is reduced by the silvered surfaces.

Q43. The shiny silvered surfaces in a thermos flask reduce heat loss by ______.
The shiny silvered surfaces in a thermos flask reflect heat and reduce heat loss by radiation. The vacuum reduces conduction and convection. The silvered surfaces are specifically for preventing radiation.

Q44. Which of the following is the best example of a heat conductor?
Aluminium is a metal and a good conductor of heat. Cork, glass, and sponge are insulators. Metals have free electrons that transfer heat quickly, making them good conductors.

Q45. Which of the following is the best example of a heat insulator?
Air is a good insulator because it is a poor conductor of heat. It traps heat and prevents transfer. Iron, copper, and steel are all good conductors of heat. This is why air is used in insulating materials like wool and thermos flasks.

Q46. The formation of clouds and thunderstorms is associated with strong ______.
The formation of clouds and thunderstorms is associated with strong convection currents in the atmosphere. Warm, moist air rises, cools, and condenses, forming clouds. Strong rising currents can lead to thunderstorms.

Q47. To demonstrate convection in air, you can hold a ______.
To demonstrate convection in air, you can hold a pinwheel above a lighted candle. The rising hot air will spin the pinwheel, showing the movement of air due to convection. A thermometer measures temperature, a metal rod shows conduction, and water in the sun shows radiation.

Q48. The earth’s atmosphere is heated by ______.
The earth’s atmosphere is heated by radiation from the sun. The air near the ground is then heated by convection, creating convection currents. Conduction is minimal in the atmosphere because air is a poor conductor.

Q49. The range of a clinical thermometer is 35°C to 42°C because ______.
The range of a clinical thermometer is 35°C to 42°C because human body temperature under normal conditions falls within this range. It is designed specifically for measuring body temperature. Cost, appearance, and ease of reading are not the reasons.

Q50. The correct method to use a clinical thermometer is to ______.
A clinical thermometer should be washed with an antiseptic solution before and after use for hygiene. It should not be washed with hot water (it may break), held by the bulb (body heat affects reading), or read in the mouth.