Physics Notes

Important Points on Heat and Thermodynamics :- Physics Dose

Important Points on Heat and Thermodynamics

General Awareness is a very important topic as far as Competitive Exams are concerned and normally a few questions from the topic Heat and Thermodynamics can be seen in every competitive exam. So, the notes provided below on the topic “Heat and Thermodynamics” should not be missed if you are preparing for any competitive exam

Heat and Thermodynamics


  • Heat is a form of energy, which measures the sensation or perception of warmness or coldness of a body or environment
  • Its unit is a calorie, kilocalorie or joule.
  • 1 calorie = 4.18 joule.


  • Temperature is the measurement of the hotness or coldness of a body.
  • When two bodies are placed in contact, heat always flows from a body at a higher temperature to the body at a lower temperature.
  • An instrument used to measure the temperature of a body is called a thermometer.
  • The normal temperature of a human body is 370C or 98.40 F
  • – 400 is the temperature at which Celsius and Fahrenheit’s thermometers read the same.
  • The clinical thermometer reads from 960F to 1100
  • The white roof keeps the house cooler in summer than the black roof because a white roof reflects more and absorbs fewer heat rays whereas the black roof absorbs more and reflects fewer heat rays.
  • Ice wrapped in a blanket does not melt away quickly because the woollen blanket is a bad conductor of heat.
  • Silver is the best conductor of heat.
  • Cooking utensils are made of aluminum, brass, and steel because these substances have low specific heat and high conductivity.

Thermal Expansion

  • Thermal expansion is the increase in the size of heating.
  • A solid can undergo three types of expansions-
    (i) Linear expansion
    (ii) Superficial expansion
    (iii) Cubical expansion
  • The relation between the coefficient of linear expansion (α), the coefficient of superficial expansion (β), the coefficient of cubical expansion (γ)
    α: β:γ = 1: 2: 3
  • Telephone wires are kept loose to allow the wires for contraction in winter.
  • A gap is provided between two iron tracks of the railway track so that rails can easily expand during summer and do not bend.

Specific Heat

  • The amount of heat required to raise the temperature of a unit mass of a substance through 10C, is called its specific heat.
  • When the temperature of the water is increased from 00C, then its volume decreases up to 40C, becomes a minimum at 40C and then increases.
  • This behavior of water around 40C is called the anomalous expansion of water.

Latent Heat

  • The heat energy absorbed or released at constant temperature per unit mass for a change of state is called the latent heat.
  • The latent heat of fusion of ice is 80 cal/g.
  • Latent heat of vaporization of steam is 536 cal/g.
  • Hot water burns are less severe than that of steam burns because steam has high latent heat.


  • It is the slow process of a conversion of a liquid into its vapour even below its boiling temperature.
  • The amount of water vapour in the air is called humidity.
  • The relative humidity is measured by the hygrometer.
  • Relative humidity increase with the increase of temperature.

Transmission of Heat

  • Transfer of heat from one place to another place is called the transmission of heat.
  • In solids, the transmission of heat takes place by the conduction process.
  • In liquids and gases, the transmission of heat takes place by convection process. In-the room, ventilators are provided to escape the hot air by convection.
  • The heat from the Sun reaches the Earth by radiation.

Simple Pendulum

  • A simple pendulum is a heavy point mass suspended from rigid support by means of an elastic and inextensible string.
  • The maximum time period of a simple pendulum is 84.6 min.
  • The time period of a simple pendulum does not depend upon the mass, shape, and size of the bob and its amplitude of oscillation. A pendulum clock goes slow in summer and fast in winter.
  • If a simple pendulum is suspended in a lift descending down with acceleration, then the time period of the pendulum will increase. If the lift is ascending, then the time period of the pendulum will decrease.
  • If a lift falling freely under gravity, then the time period of the pendulum is infinite.

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