Exercise Solutions (From Screenshot Page 103)

Q1: Fill in the blanks.

1. Heat is a form of energy.
2. Temperature is a measure of the degree of hotness or coldness.
3. The SI unit of temperature is Kelvin (K).
4. The range of a clinical thermometer is 35°C to 42°C.
5. The range of a laboratory thermometer is -10°C to 110°C.
6. Most substances expand on heating and contract on cooling.
7. Water shows anomalous expansion between 0°C and 4°C.
8. The hidden heat absorbed or released during a change of state is called latent heat.
9. The amount of heat required to raise the temperature of a unit mass of a substance by 1°C is called specific heat capacity.
10. Heat transfer through direct contact is called conduction.
11. Heat transfer by the movement of fluid particles is called convection.
12. Heat transfer in the form of electromagnetic waves is called radiation.
13. Materials that allow heat to pass through them easily are called conductors.
14. Materials that do not allow heat to pass through them easily are called insulators.

Q2: Match the pairs.

(Note: As an AI, I cannot create interactive matching. I will provide the correct pairs.)

• Clinical thermometer - Measures body temperature
• Laboratory thermometer - Measures temperature of substances
• Celsius - 0°C freezing point of water
• Fahrenheit - 32°F freezing point of water
• Kelvin - SI unit of temperature
• Melting - Solid to liquid
• Boiling - Liquid to gas
• Freezing - Liquid to solid
• Sublimation - Solid directly to gas
• Conduction - Heat transfer in solids
• Convection - Heat transfer in fluids
• Radiation - Heat transfer without medium

Q3: Give scientific reasons.

1. Gaps are left between railway tracks.
   Reason: Gaps are left between railway tracks to allow for the thermal expansion of the metal tracks during hot summer days. Metals expand significantly when heated. If no gaps were left, the expanding tracks would push against each other, causing them to buckle and deform, which could lead to train derailments and accidents.
2. Steam causes more severe burns than boiling water at the same temperature.
   Reason: Steam at 100°C contains additional energy in the form of 'latent heat of vaporization' compared to boiling water at 100°C. When steam comes into contact with the skin, it condenses into water, releasing this large amount of latent heat. This extra heat energy causes more severe and deeper burns than boiling water, which only transfers its sensible heat.
3. Water is used as a coolant in car radiators.
   Reason: Water has a very high specific heat capacity. This means it can absorb a large amount of heat energy from the hot engine without its own temperature rising significantly. This property allows water to effectively carry away excess heat from the engine, keeping it cool and preventing overheating, thus acting as an efficient coolant.
4. Aquatic life survives in ponds even when the surface freezes.
   Reason: This is due to the anomalous expansion of water. Water has maximum density at 4°C. As the surface water cools to 4°C, it becomes denser and sinks to the bottom. Water below 4°C (e.g., 3°C, 2°C, 1°C, 0°C) is less dense and remains on the surface, where it eventually freezes. This forms a layer of ice on top, which acts as an insulator, preventing the water below (at 4°C) from freezing, thus allowing aquatic life to survive in the warmer water at the bottom.

Q4: Answer the following questions.

1. Differentiate between heat and temperature.
   Answer:

   Feature	Heat	Temperature
   Nature	Form of energy transferred	Measure of hotness/coldness (average kinetic energy)
   Flow	Flows from higher to lower temperature	Indicates direction of heat flow
   Unit (SI)	Joule (J)	Kelvin (K)
   Measurement	Calorimeter	Thermometer

2. Explain the different types of thermometers.
   Answer:
   • Clinical Thermometer: Used to measure human body temperature. Range: 35°C to 42°C. Has a kink near the bulb to hold mercury level for reading.
   • Laboratory Thermometer: Used for general laboratory purposes. Range: -10°C to 110°C. No kink, so mercury level falls quickly. Must be held vertically during reading.
   • Digital Thermometer: Modern, mercury-free thermometers that use electronic sensors to provide quick and accurate temperature readings. Safer and environmentally friendly.
3. Explain the effects of heat on matter.
   Answer: Heat has several effects on matter:
   • Expansion and Contraction: Most substances expand (increase in size) when heated and contract when cooled. This applies to solids, liquids, and gases (e.g., gaps in railway tracks). Water shows anomalous expansion (contracts from 0°C to 4°C, then expands).
   • Change of State: Heat can cause a substance to change its physical state.
     • Melting (solid to liquid), Boiling (liquid to gas)
     • Freezing (liquid to solid), Condensation (gas to liquid)
     • Sublimation (solid directly to gas, e.g., camphor).
   • Latent Heat: Heat absorbed or released during a change of state at constant temperature (e.g., latent heat of fusion for melting, latent heat of vaporization for boiling).
   • Specific Heat Capacity: The amount of heat required to raise the temperature of a unit mass of a substance by 1°C. Different substances have different specific heat capacities.
4. Explain the different modes of heat transfer.
   Answer: Heat can be transferred by three modes:
   • Conduction: Heat transfer through direct contact between particles, without the actual movement of the medium. Occurs mainly in solids (e.g., heating a metal rod). Good conductors (metals) and poor conductors/insulators (wood, plastic).
   • Convection: Heat transfer by the actual movement of fluid (liquid or gas) particles. Heated fluid becomes less dense and rises, while cooler fluid sinks, creating convection currents (e.g., boiling water, sea breezes).
   • Radiation: Heat transfer in the form of electromagnetic waves (infrared radiation), which does not require any medium. It can travel through a vacuum (e.g., heat from the sun, heat from a fire).

Q5: Differentiate between.

1. Conductors and Insulators of Heat
   

   Feature	Conductors	Insulators
   Heat Transfer	Allow heat to pass through easily	Do not allow heat to pass through easily
   Examples	Metals (Copper, Aluminium, Iron)	Wood, Plastic, Air, Wool, Glass
   Application	Cooking utensils, electrical wires	Handles of utensils, woolen clothes, building insulation

2. Melting and Boiling
   

   Feature	Melting (Fusion)	Boiling (Vaporization)
   Change of State	Solid to Liquid	Liquid to Gas
   Temperature	Occurs at melting point (constant temperature)	Occurs at boiling point (constant temperature)
   Heat Involved	Latent heat of fusion absorbed	Latent heat of vaporization absorbed
   Example	Ice turning into water	Water turning into steam