UNIT NO.10
Heat and Temperature
(Solved Exercise)
10.2 Give short answers.
1 Define heat.
The energy that transfers from one object to another because of a temperature difference
between them is called heat.
2. Name three modes of heat transfer.
i. Conduction ii. Convection iii. Radiation
3. Which two temperatures are the base of Celsius and Fahrenheit temperature scales?
The temperatures of melting ice and boiling water are the base of Celsius and Fahrenheit temperature scales.
4. Give five examples of good conductors of heat.
Iron, copper, silver, gold and aluminium metals are the examples of good conductors of heat.
5. Give five examples of bad conductors of heat.
Wood, rubber, plastic, paper and glass, etc., are the examples of bad conductors of heat.
10.3 Constructed Response Questions
1. How are expansion and contraction useful in thermometers?
Answer:
Expansion and contraction are most important in thermometers as they enable the measurement of temperature changes. When temperature increases, the liquid inside the thermometer expands, causing the level to rise. Conversely, a decrease in temperature leads to contraction, lowering the liquid level. This change in volume serves as a reliable indicator of temperature variations, allowing accurate temperature readings in various applications.
2. Explain why hot air balloons rise up.
Answer:
Hot air balloons rise because hot air is lighter than cold air. When the air inside the balloon is heated, it becomes less dense and lighter. Since the hot air is lighter than the cooler air around it, the balloon floats upward. This is because lighter things tend to go up, just like a helium balloon rises in the air. The hot air inside the balloon makes it buoyant, allowing it to lift off the ground and fly.
3. What does amongst the solid, liquid or gas expand fast and why?
Answer:
Among solids, liquids, and gases, gases expand the fastest. This is because the particles in a gas are spread out and move very quickly. When you heat a gas, the particles gain even more energy, causing them to move faster and spread out even more. This rapid movement and increased spacing result in the gas expanding quickly. In contrast, solids have particles that are closely packed, and liquids fall in between gases and solids in terms of particle arrangement and movement.
4. Expansion and contraction can be helpful in many areas of life. Explain.
Answer:
Expansion and contraction play vital roles in everyday life. They are crucial in designing structures that can withstand temperature changes, like bridges and roads. In cooking, they influence the rising and setting of dough. Thermometers use expansion and contraction to measure temperature accurately. Overall, these phenomena have widespread applications in engineering, construction, and various scientific instruments.
5. What do you mean by kinetic energy of particles?
Answer:
Kinetic energy of particles refers to the energy they have due to their motion. In simple terms, when particles move, they possess kinetic energy. The faster they move, the more kinetic energy they have. This concept helps us understand the behavior of matter in different states, like solid, liquid, and gas.
6. Substances do not expand or contract at the same rate. Why?
Answer:
Substances have different structures, causing them to expand or contract at varying rates. The arrangement of particles in each substance affects how they respond to heat. Some substances have particles that are closely packed, leading to slower expansion or contraction, while others may have more loosely arranged particles, resulting in faster changes in size with temperature. So, it depends on the substance’s composition and structure.
7. Describe the uses of expansion and contraction of liquids.
Answer:
Expansion and contraction of liquids are important in various ways:
- Thermometers: Liquid inside expands and rises when heated, allowing us to measure temperature.
- Pipelines: Helps prevent damage by accommodating changes in liquid volume due to temperature variations.
- Cooking: Liquids like water expand when heated, influencing the cooking process.
- Weather Instruments: Instruments like barometers use the expansion and contraction of liquids to measure atmospheric pressure.