Short Questions
1. What is heat?
- Heat is a form of energy that flows from a hot object to a cold object.
2. What is the SI unit of heat?
- The SI unit of heat is Joule (J).
3. What is the CGS unit of heat?
- The CGS unit of heat is Calorie (cal).
4. What is temperature?
- Temperature measures how hot or cold an object is.
5. What are the three units of temperature?
- Celsius (°C), Fahrenheit (°F), and Kelvin (K).
6. What is the normal body temperature in Fahrenheit?
- 98.6°F.
7. What is the boiling point of water in Celsius?
- 100°C.
8. What is the freezing point of water in Celsius?
- 0°C.
9. Which instrument is used to measure temperature?
- Thermometer.
10. What is a calorimeter used for?
- A calorimeter is used to measure the heat transfer in substances.
11. What happens to most objects when heated?
- Most objects expand when heated.
12. What is thermal expansion?
- Thermal expansion is the increase in the size of a substance when heated.
13. Why do railway tracks have small gaps between them?
- To allow expansion in hot weather and prevent damage.
14. Why is mercury used in thermometers?
- Because it expands evenly and does not stick to glass.
15. What is specific heat capacity?
- It is the amount of heat needed to raise the temperature of 1 kg of a substance by 1°C.
16. Which metal expands the most when heated?
- Aluminum expands the most.
17. What is the formula to convert Celsius to Fahrenheit?
- F = (9/5 × C) + 32.
18. What is the formula to convert Celsius to Kelvin?
- K = C + 273.15.
19. What is conduction?
- Heat transfer in solids from one particle to another without moving the substance.
20. What is convection?
- Heat transfer in liquids and gases by the movement of particles.
Long Questions
1. What is the difference between heat and temperature?
- Heat is the total energy of all molecules in a substance, while temperature measures the average kinetic energy of molecules. Heat is measured in Joules (J), and temperature is measured in °C, °F, or K.
2. What are the three types of heat transfer?
- Heat can transfer by conduction, convection, and radiation. Conduction happens in solids, convection in liquids and gases, and radiation transfers heat without needing a medium.
3. Why do metal bridges have expansion joints?
- Metals expand when heated, so bridges have gaps to allow for expansion and prevent bending or cracking. Without these joints, the bridge could become damaged in hot weather.
4. Why is water used in car radiators?
- Water has a high specific heat capacity, which means it can absorb and store a large amount of heat. This helps cool the car engine and prevents it from overheating.
5. What is the principle of a thermometer?
- A thermometer works on thermal expansion, where liquids like mercury or alcohol expand when heated. The rise in liquid level indicates the temperature of an object.
6. What happens when a liquid is heated?
- When a liquid is heated, its molecules move faster, expand, and its density decreases. This causes convection currents, which are important in boiling water, ocean currents, and weather changes.
7. Why does a bimetallic strip bend when heated?
- A bimetallic strip has two metals that expand at different rates when heated. One metal expands more, causing the strip to bend, which is used in thermostats and fire alarms.
8. How does a calorimeter measure heat?
- A calorimeter is a device with insulated walls that measures heat transfer. The heat lost by a hot object is equal to the heat gained by a cooler substance, allowing heat energy to be calculated.
9. Why do gases expand more than solids and liquids?
- Gas molecules are far apart and move freely, so when heated, they move faster and spread out more. This is why hot air rises, balloons expand, and gas pressure increases in a closed container.
10. Why do we feel hot near a fire even without touching it?
- Heat from fire reaches us through radiation, which does not need a medium to transfer. This is the same way the Sun’s heat reaches Earth through space.
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