Heat and Temperature Concepts

Heat and Temperature

• Heat is the transfer of energy between two bodies at different temperatures.
• Temperature measures how hot or cold a body is.
• Heat energy flows from hotter to colder bodies in contact.

Units of Heat

• The SI unit of heat is the joule (J).
• The CGS unit of heat is the erg.
• 1 joule = 10⁷ erg
• Other units include calorie (cal) and kilocalorie (kcal).
• 1 kilocalorie = 1000 calories
• 1 calorie = 4.186 joules (approximately 4.2 joules).

Units of Temperature

• The SI unit of temperature is the Kelvin (K).
• Other common units are degrees Celsius (°C) and degrees Fahrenheit (°F).
• The relationship between Kelvin and Celsius is: K = °C + 273.

Difference Between Heat and Temperature

• Heat is energy transfer; temperature is the measure of average kinetic energy of particles in a substance.
• The amount of heat in a body depends on mass, temperature, and material.
• Temperature only depends on the average kinetic energy of particles.
• Heat flow occurs due to temperature difference; temperature is the driving force for heat flow.

Thermal Expansion

• Most substances expand when heated and contract when cooled.
• Solids, liquids, and gases all experience thermal expansion.
• Expansion can be linear, superficial, or cubical.
• Liquids and gases primarily experience volumetric or cubical expansion.
• Water exhibits anomalous expansion between 0°C and 4°C.

Anomalous Expansion of Water

• Water expands when heated from 0°C to 4°C.
• Water contracts when heated above 4°C and expands when cooled to 0°C.

Energy Flow in Ecosystems

• The flow of energy through an ecosystem is unidirectional, starting from the sun.
• Producers (plants) capture solar energy through photosynthesis.
• Primary consumers eat producers, secondary consumers eat primary consumers, and so on.
• Energy is lost as heat at each trophic level in respiration and other metabolic processes.
• A fraction of energy is also lost due to waste and unuseful energy forms.

Sources of Energy

• Renewable sources: These can be replenished and are often sustained by natural processes. Examples include solar, wind, hydro, biomass, tidal, and geothermal energy.
• Non-renewable sources: These have finite supplies and are depleted as they are used. Examples include coal, petroleum, and natural gas.

Production of Electricity from Renewable Sources

• Solar energy: Solar cells convert sunlight directly into electricity. Solar power plants use concentrated sunlight to heat water and generate steam for electricity.
• Wind energy: Wind turbines harness wind energy to rotate a generator and produce electricity.
• Hydroelectric energy: Water flowing through a dam turns turbines connected to generators to produce electricity.
• Bioenergy: Biomass (organic matter) is burned to produce heat, then converted to energy.
• Nuclear energy: Nuclear fission reactions produce heat to boil water, generate steam, and produce electricity.

Judicious Use of Energy

• Using energy resources responsibly and preventing waste.
• Prioritizing renewable sources.
• Conserving energy, especially through efficient use.