Heat

Heat is a form of energy that flows from a hotter body to a colder body due to temperature difference.
It is measured in Joule (SI unit) or calorie.
In Bihar, understanding heat is essential for:

• Weather forecasting (heat waves, Loo winds)
• Agriculture (soil heating, crop cycles)
• Health care (heat stroke, thermoregulation)
• Energy-saving building designs

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Temperature vs Heat

• Heat = Energy in transit
• Temperature = Intensity of heat

📝 PYQ (BPSC): SI unit of heat? → Joule
📝 Expected MCQ: What measures degree of hotness? → Temperature

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Modes of Heat Transfer

1. Conduction

• Heat flows through solids without movement of particles
• Example: Iron rod heated at one end becomes hot throughout
• Good conductors: Copper, Aluminium
• Poor conductors: Wood, Plastic

📝 Expected MCQ: Best conductor of heat? → Silver
📝 Expected MCQ: Conduction occurs in? → Solids

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2. Convection

• Transfer through fluids (liquids/gases) via particle movement
• Example: Boiling water, sea breeze
• Hot particles rise, cool particles sink → convection currents

📝 PYQ (BPSC CDPO): Sea breeze occurs due to? → Convection

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3. Radiation

• Transfer of heat in form of electromagnetic waves
• Does not need a medium
• Example: Sun’s heat reaches Earth, black objects absorb more radiation

📝 PYQ (BPSC): Heat from the Sun reaches Earth by? → Radiation

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Effects of Heat

1. Expansion

• Solids, liquids, gases expand on heating
• Used in railway tracks, bridges (expansion joints)

2. Change of State

• Solid ↔ Liquid ↔ Gas transitions
• Example: Ice melts to water; water vaporizes

3. Change in Temperature

• Depends on specific heat capacity
• Water has high specific heat → moderates climate

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Measurement of Heat & Temperature

• Thermometer: Measures temperature
  • Clinical: 35°C – 42°C
  • Lab: Up to 100°C
• Calorimeter: Measures heat gained/lost
• Thermocouple: Measures very high temperatures

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Heat & Human Body (Bihar Context)

• Heatstroke: Common in Bihar's summer (Loo winds)
• Precaution: hydration, ORS, shade
• Solar cookers use black surfaces (absorb radiation)
• BREDA promotes passive solar buildings for heat reduction

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Latent Heat

• Heat required to change state without changing temperature
• Types:
  • Latent heat of fusion: Ice to water
  • Latent heat of vaporization: Water to steam

📝 Expected MCQ: Ice melting without temperature change is due to? → Latent heat

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Specific Heat

• Heat required to raise 1g of substance by 1°C
• Water has highest specific heat → used in cooling systems

📝 PYQ: Why is water used in car radiators? → High specific heat

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Applications of Heat

• Solar cookers, greenhouses, industrial furnaces
• Geothermal heating in power generation
• Infrared thermometers used in health centers
• ISRO satellites track surface heat, used by Bihar’s agri-mapping

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PYQs + Expected MCQs

📝 PYQ (BPSC): Mode of heat transfer from Sun to Earth? → Radiation
📝 PYQ: SI unit of heat? → Joule
📝 PYQ: Why is water used in radiators? → High specific heat
📝 PYQ (BPSC CDPO): Sea breeze occurs due to? → Convection
📝 Expected MCQ: Which metal conducts heat best? → Silver
📝 Expected MCQ: Which mode of heat transfer does not require a medium? → Radiation
📝 Expected MCQ: What measures heat content of a substance? → Calorimeter

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Quick Revision Points

• Heat = Energy in transit
• Temperature = Degree of hotness
• SI unit of Heat = Joule
• Transfer Modes:
  • Conduction: Solids
  • Convection: Liquids/Gases
  • Radiation: No medium
• Latent heat: Phase change
• Specific heat: Water is highest
• Bihar: Heat wave → Loo, Solar cookers, BREDA schemes

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Sources Used

• NCERT Class 7–10 Science
• Lucent GK – Physics Section
• Drishti Science & Tech Quick Book
• EduTeria PYQs
• Ghatna Chakra BPSC PYQs
• Bihar State Disaster Reports (Heat Wave Data)
• BREDA Bihar Solar Energy Programs