मराठी
Maharashtra State BoardHSC Science (Computer Science) 11th Standard
पाठ्यपुस्तक उत्तरे७४०२
संकल्पना स्पष्टीकरण आणि व्हिडिओ५२०
अभ्यासक्रम

Heat Transfer

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Topics

Estimated time: 8 minutes
  • Classification
  • Key Points: Heat Transfer

Classification

Heat may be transferred from one point of a body to another through three different ways — conduction, convection, and radiation.

Conduction

  • Heat transfers through solids by conduction.
  • In this process, heat is passed on from one molecule to another molecule.
  • The molecules do not leave their mean positions during this process.
  • Conduction is a slow process of heat transfer.
  • A material medium is required to transfer heat by conduction.

Convection

  • Liquids and gases are heated by convection.
  • In this process, there is a bodily movement of the heated molecules.
  • Convection is a rapid process of heat transfer.
  • A material medium is required to transfer heat by convection.

Radiation

  • Transfer of heat by radiation does not need any medium.
  • Radiation of heat energy takes place by electromagnetic (EM) waves.
  • These EM waves travel with a speed of 3×10⁸ ms⁻¹ in space/vacuum.
  • The energy from the Sun comes to us by radiation.
  • Radiation is the fastest process of heat transfer because heat transfer takes place at the speed of light.
Maharashtra State Board: Class 11

Key Points: Heat Transfer

  • Heat can be transferred in three ways — conduction, convection, and radiation.
  • Conduction transfers heat through solids; molecules vibrate but do not move from their positions.
  • Convection transfers heat through liquids and gases; molecules physically move from place to place.
  • Both conduction and convection require a material medium; radiation does not.
  • Radiation travels through electromagnetic waves at a speed of 3×10⁸ ms⁻¹.
  • Conduction is the slowest process, convection is rapid, and radiation is the fastest mode of heat transfer.
  • The energy received from the Sun is an example of heat transfer by radiation.

Test Yourself

Related QuestionsVIEW ALL [19]

A thin square steel plate with each side equal to 10 cm is heated by a blacksmith. The rate of radiated energy by the heated plate is 1134 watts. The temperature of the hot steel plate is ______.

(Stefan's constant σ = 5.67 × 10-8 watt m-2K-4 emissivity of the plate = 1)

An electric heater is used in a room with a total wall area of 137 m2 to maintain a temperature of +20°C inside it when the outside temperature is -10°C. The walls have three different layers of materials. The innermost layer is of wood of thickness 2.5 cm, the middle layer is of cement of thickness 1.0 cm and the outermost layer is brick of 25.0 cm. The power of the electric heater will be ______ W. Assume that there is no heat loss through the floor and the ceiling. The thermal conductivities of wood, cement, and brick are 0.125, 1.5, and 1.0 watt/m/°C respectively.

A ring consisting of two parts ADB and ACB of same conductivity K carries an amount of heat H. The ADB part is now replaced with another metal keeping the temperatures T1 and T2 constant. The heat carried increases to 2H. What should be the conductivity of the new ADB part? (Given `"ACB"/"ADB"` = 3)

 

Answer the following question.

Define coefficient of thermal conductivity.

Two rectangular blocks A and B of different metals have same length and same area of cross-section. They are kept in such a way that their cross-sectional area touch each other. The temperature at one end of A is 100°C and that of B at the other end is 0°C. If the ratio of their thermal conductivity is 1 : 3, then under steady state, the temperature of the junction in contact will be ______.

Answer the following question.

Explain the term 'steady state'.

Solve the following problem.

Find the temperature difference between two sides of a steel plate 4 cm thick, when the heat is transmitted through the plate at the rate of 400 k cal per minute per square meter at a steady state. Thermal conductivity of steel is 0.026 kcal/m s K.

Solve the following problem.

An electric kettle takes 20 minutes to heat a certain quantity of water from 0 °C to boiling point. It requires 90 minutes to turn all the water at 100 °C into steam. Find the latent heat of vaporization. (Specific heat of water = 1 cal/g °C)

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