Heat

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Q1. Heat is a form of ______.
Heat is a form of energy that flows from a hotter body to a colder body. It is not a substance like liquid, solid, or gas. Heat energy is measured in joules (J) and is the total kinetic energy of the particles in a substance.

Q2. The SI unit of temperature is ______.
The SI unit of temperature is Kelvin (K). Celsius and Fahrenheit are also units of temperature but are not SI units. Joule is the SI unit of energy and work, not temperature.

Q3. The device used to measure temperature is called a ______.
A thermometer is used to measure temperature. A barometer measures atmospheric pressure, a voltmeter measures voltage, and an ammeter measures electric current. The thermometer is the correct instrument for measuring temperature.

Q4. On the Celsius scale, the boiling point of water is ______.
On the Celsius scale, the boiling point of water is 100°C. 0°C is the freezing point, 32°C is not a standard reference point, and 212°F is the boiling point on the Fahrenheit scale.

Q5. On the Celsius scale, the freezing point of water is ______.
On the Celsius scale, the freezing point of water is 0°C. 100°C is the boiling point, 32°F is the freezing point on the Fahrenheit scale, and -10°C is a temperature below freezing.

Q6. A clinical thermometer is used to measure the ______ of the human body.
A clinical thermometer is specifically designed to measure the temperature of the human body. Humidity is measured by a hygrometer, blood pressure by a sphygmomanometer, and pulse rate by counting heartbeats.

Q7. The normal temperature of the human body is about ______.
The normal temperature of the human body is about 37°C, which is equivalent to 98.6°F. 98.6°C is too high, 98°F is close but not exact, and 100°C is the boiling point of water.

Q8. The range of a clinical thermometer is usually from ______.
A clinical thermometer has a range from 35°C to 42°C because human body temperature falls within this range. 0°C to 100°C is the range of a laboratory thermometer, -10°C to 110°C is for some lab thermometers, and 30°C to 50°C is not standard.

Q9. Before using a clinical thermometer, we should ______ it to bring the mercury level down.
Before using a clinical thermometer, we should shake it firmly to bring the mercury level down. This is necessary because the kink prevents the mercury from falling back on its own. Heating, cooling, or dipping in water would not effectively bring the mercury level down.

Q10. The purpose of the kink in a clinical thermometer is to ______.
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. It does not affect temperature or appearance.

Q11. A laboratory thermometer is used to measure temperature in a ______.
A laboratory thermometer is used in laboratories for measuring temperatures in experiments. It is not used for measuring human body temperature (clinical thermometer is used for that). It can be used in ovens or freezers but the primary setting is a laboratory.

Q12. The range of a typical laboratory thermometer is ______.
A typical laboratory thermometer has a range from -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 for general laboratory use.

Q13. A laboratory thermometer does NOT have 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 stem, and usually contain mercury or alcohol.

Q14. While reading a thermometer, the level of mercury should be ______.
While reading a thermometer, the mercury level should be at the same level as the eye to avoid parallax error. This ensures accurate reading. Reading from above or below can give incorrect values.

Q15. While using a laboratory thermometer to heat a liquid, the bulb should ______.
When heating a liquid with a laboratory thermometer, the bulb should not touch the bottom or sides of the beaker to get an accurate reading of the liquid’s temperature. Touching the glass would give the temperature of the container, not the liquid.

Q16. The process by which heat flows from a hotter part of a solid to a cooler part is called ______.
Conduction is the process of heat transfer in solids, where heat flows from the hotter end to the cooler end through the vibration of particles. Convection occurs in liquids and gases, radiation does not need a medium, and insulation prevents heat transfer.

Q17. Which of the following is the best conductor of heat?
Iron is a metal and is a good conductor of heat. Wood, plastic, and air are poor conductors (insulators). Metals like iron, copper, and aluminium are good conductors because they have free electrons that transfer heat quickly.

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

Q19. The handles of cooking utensils are often made of wood or plastic because they are ______.
Handles of cooking utensils are made of wood or plastic because they are bad conductors (insulators) of heat. This prevents heat from passing from the hot utensil to your hand, making it safe to hold. Good conductors would burn your hand.

Q20. The mode of heat transfer in liquids and gases is called ______.
Convection is the mode of heat transfer in liquids and gases, where heated particles move and carry heat with them. Conduction occurs in solids, radiation does not need a medium, and insulation prevents heat transfer.

Q21. Which of the following is an example of heat transfer by convection?
Sea and land breezes are caused by convection currents in the air. A metal spoon heating up is conduction, the sun warming the earth is radiation, and touching a hot plate is conduction. Convection involves the movement of the medium itself.

Q22. The mode of heat transfer that does not require any medium is called ______.
Radiation is the mode of heat transfer that does not require any medium. Heat from the sun reaches the Earth through radiation. Conduction and convection both require a medium, and reflection is not a mode of heat transfer.

Q23. The heat from the sun reaches the Earth by the process of ______.
The heat from the sun reaches the Earth by radiation because there is a vacuum in space and no medium for conduction or convection. Radiation travels through electromagnetic waves.

Q24. While reading a clinical thermometer, you should hold it in a ______ position.
A clinical thermometer should be held in a vertical position while reading to allow the mercury to settle properly and to get an accurate reading. Holding it horizontally or tilted may cause difficulty in reading the scale.

Q25. Which liquid is commonly used in a thermometer?
Alcohol or mercury is commonly used in thermometers because they expand and contract uniformly with temperature changes. Water is not used because it expands anomalously, and oil and kerosene are not suitable for accurate temperature measurement.

Q26. In a clinical thermometer, the temperature is usually marked in ______.
Clinical thermometers typically have both Fahrenheit and Celsius scales marked on them. Kelvin is the SI unit but is not commonly used in clinical thermometers. Only Fahrenheit is also not correct, as both scales are usually present.

Q27. The boiling point of water on the Fahrenheit scale is ______.
On the Fahrenheit scale, the boiling point of water is 212°F. 32°F is the freezing point, 100°F is close to human body temperature, and 0°F is a temperature below freezing.

Q28. The freezing point of water on the Fahrenheit scale is ______.
On the Fahrenheit scale, the freezing point of water is 32°F. 212°F is the boiling point, 100°F is close to human body temperature, and 0°F is a temperature below freezing.

Q29. In which mode of heat transfer does the medium itself move?
In convection, the medium itself moves. Heated particles rise and cooler particles sink, creating convection currents. In conduction, particles vibrate but do not move as a bulk. Radiation does not require a medium.

Q30. Dark-coloured surfaces are ______ absorbers of heat.
Dark-coloured surfaces are good absorbers of heat. This is why we wear dark clothes in winter to absorb heat and keep warm. Light-coloured surfaces reflect heat.

Q31. Shiny, white surfaces are ______ reflectors of heat.
Shiny, white surfaces are good reflectors of heat. They reflect heat rather than absorb it, which is why we wear light-coloured clothes in summer to stay cool.

Q32. Why are cooking vessels generally made of metal?
Cooking vessels are made of metal because metals are good conductors of heat. This allows heat to transfer quickly from the source to the food inside. Poor conductors would not heat food efficiently.

Q33. Why do we wear light-coloured clothes in summer?
Light-coloured clothes reflect heat, keeping us cool in summer. Dark-coloured clothes absorb heat, which is why they are worn in winter. Comfort and cost are not the primary reasons.

Q34. Why do we wear dark-coloured clothes in winter?
Dark-coloured clothes absorb heat, which keeps us warm in winter. Light-coloured clothes reflect heat, which is why they are worn in summer. Fashion and availability are not the primary reasons.

Q35. A thermos flask keeps hot liquids hot by minimising all modes of heat transfer. Which mode is minimised by the vacuum between its two walls?
The vacuum between the two walls of a thermos flask minimises heat transfer by conduction and convection because there is no medium for heat to travel through. Radiation is minimised by the silvered surfaces, not the vacuum.

Q36. In a thermos flask, the silvered surfaces help to reduce heat loss by ______.
The silvered surfaces in a thermos flask reflect heat and reduce heat loss by radiation. The vacuum reduces conduction and convection. The stopper also helps reduce heat loss.

Q37. The process of heat transfer in which a bulk movement of molecules takes place is known as:
Convection involves the bulk movement of molecules, where heated particles rise and cooler particles sink, creating currents. Conduction involves the transfer of heat through particle vibration, and radiation does not require a medium.

Q38. Land breeze is a phenomenon that occurs due to:
Land breeze occurs due to convection currents in the air. At night, land cools faster than the sea, causing air above the land to cool and sink, creating a breeze from land to sea. This is a convection phenomenon.

Q39. Sea breeze is a phenomenon that occurs due to:
Sea breeze occurs due to convection currents in the air. During the day, land heats up faster than the sea, causing air above the land to rise and cooler air from the sea to move in, creating a breeze from sea to land. This is a convection phenomenon.

Q40. When we touch a piece of iron and a piece of wood kept in the same room, the iron feels colder. Why?
Iron feels colder because it is a better conductor of heat and draws heat away from our hand faster. Both are at the same temperature, but the iron transfers heat more quickly, creating the sensation of coldness.

Q41. What is the name of the liquid metal used in some thermometers?
Mercury is a liquid metal used in some thermometers. It expands and contracts uniformly with temperature changes. Alcohol is also used, but it is not a metal. Water and oil are not used in thermometers.

Q42. The kink in a clinical thermometer is also known as a ______.
The kink in a clinical thermometer is also called a constriction. It prevents the mercury from falling back after a reading is taken. The bulb contains the mercury, the stem is the tube, and the scale is the marked measurements.

Q43. After taking a reading, why must you give a firm jerk to a clinical thermometer before the next use?
After taking a reading, you must give a firm jerk to a clinical thermometer to bring the mercury level down. This is because the kink holds the mercury in place. Shaking it forces the mercury back into the bulb for the next use.

Q44. Which of the following is a good example of a heat insulator?
A woollen blanket is a good heat insulator because it traps air between its fibres and reduces heat loss. Copper wire, iron nail, and aluminium foil are good conductors of heat. Insulators are poor conductors.

Q45. Which of the following is NOT a mode of heat transfer?
Reflection is not a mode of heat transfer. The three modes of heat transfer are conduction, convection, and radiation. Reflection is a phenomenon related to light and sound, not heat transfer.

Q46. Why should a clinical thermometer not be washed with hot water?
A clinical thermometer should not be washed with hot water because the mercury inside will expand too much and may break the thermometer. Hot water can cause the mercury to expand beyond the thermometer’s range, leading to breakage.

Q47. The bulb of a thermometer is usually made of ______.
The bulb of a thermometer is usually made of glass because it is a good conductor of heat and allows the liquid inside to expand or contract quickly. Glass is also transparent, allowing the liquid level to be seen.

Q48. When we heat a substance, its molecules gain energy and start moving faster. This causes the substance to ______.
When we heat a substance, its molecules gain energy and start moving faster, causing the substance to expand. This is called thermal expansion. Most substances expand on heating and contract on cooling.

Q49. Which of the following will heat up faster when kept in the sun for the same time?
A dull black cup will heat up faster because dark, rough surfaces are good absorbers of heat. Shiny silver surfaces reflect heat, a glass of water heats up slower due to water’s high specific heat, and plastic is a poor conductor.

Q50. The stopper of a thermos flask is often made of plastic or cork. This is to prevent heat loss by ______.
The stopper of a thermos flask is made of plastic or cork to prevent heat loss by conduction and convection. These materials are poor conductors and prevent air from circulating, reducing heat loss. Radiation is minimised by silvered surfaces, not the stopper.