Class 9th Physics Chapter 9 Question Answer

Complete Notes of Class 9th Physics Chapter 9 Question Answer Heat Transfer Numericals in 9th Class Physics Urdu Medium written by Sir Fahad Abbas Suib. These computerized notes are very helpful in the preparation of Heat Transfer Numericals for students of the Class 9th Physics Chapter 9 Question Answer these are according to the paper patterns of all Punjab boards.

• Important Values and Important Formulas
• Heat Transfer Exercise Numericals with Solutions in Urdu 
• Recall that thermal energy is transferred from a region of higher temperature to a region of lower temperature.
• Describe in terms of molecules and electrons , how heat transfer occurs in solids.
• State the factors affecting the transfer of heat through solid conductors and hence, define the term Thermal Conductivity.
• Solve problems based on thermal conductivity of solid conductors.
• Write examples of good and bad conductors of heat and describe their uses.
• Explain the convection currents in fluids due to difference in density.
• State some examples of heat transfer by convection in everyday life.
• Explain that insulation reduces energy transfer by conduction.
• Describe the process of radiation from all objects.
• Describe convection in water heating by putting a few pinky crystals in a round bottom flask.
• Explain that water is a poor conductor of heat.
• Investigate the absorption of radiation by a black surface and silvery surfaces using Leslie cube.
• Investigate the emission of radiation by a black surface and silvery surfaces using Leslie cube.
• Describe the use of cooking utensils, electric kettle, air conditioner, refrigerator cavity wall insulation, vacuum flask and household hotwater system as a consequence of heat transmission Processes.
• Heat is an important form of energy. It is necessary for our survival. We need it to cook our food and to maintain our body temperature. Heat is also needed in various industrial processes. How to protect ourselves from high as well as low temperature, needs knowledge of how heat travels. In this unit, we will study various ways of heat transfer.
• Transfer of heat class 9: Recall what happens when two bodies at different temperature are in thermal contact with each other. Thermal energy from a hot body flows to a cold body in the form of heat. This is called as transfer of heat. Transfer of heat is a natural process. It continues all the time as long as the bodies in thermal contact are at different temperature. There are three ways by which transfer of heat takes place. These are; Conduction, Convection and Radiation
• Conduction class 9: The handle of metal spoon held in hot water soon gets warm. But in case of a wooden spoon, the handle does not get warm.
• They also collide with their neighbouring atoms or molecules. In doing so, they pass some of their energy to neighbouring atoms or molecules during collisions with them with the increase in their vibrations. These atoms or molecules in turn pass on a part of the energy to their neighbouring particles. In this way some heat reaches the other parts of the solids. This is a slow process and very small transfer of heat takes place from hot to cold parts in solids.
• Define conduction class 9: "The mode of transfer of heat by vibrating atoms and free electrons in solids from hot to cold parts of a body is called conduction of heat".
• All metals are good conductors of heat. The substances through which heat does not conduct easily are called bad conductors or insulators. Wood, cork, cotton, wool, glass, rubber, etc. are bad conductors or insulators.
• Thermal conductivity class 9:
• "The amount of heat that flows in unit time is called the rate of flow of heat". Thus Rate of flow of heat = Q / t , It is observed that the rate at which heat flows through a solid object depends upon various factors.
• CROSS-SECTIONAL AREA OF THE SOLID: Larger cross-sectional area A of a solid contains larger number of molecules and free electrons on each layer parallel to its cross-sectional area and hence greater will be the rate of flow of heat through the solid. Thus,   Rate of flow of heat   Q / t K A