Ch 9 Phy Class 9
Important Easy Notes of Ch 9 Phy Class 9 English Medium written by Professor Mr. Samiullah Suib. These notes are very helpful in the preparation of Physics for students of the 9th class Physics English Medium and these are according to the paper patterns of all KPK Book Boards.
Summary and Contents:
Topics which are discussed in the notes are given below:
- Definition of transfer of heat also write its cause.
- Modes (Ways) of transfer of heat: (i) Conduction of heat (ii) Convection of heat (iii) Radiation of heat.
- Definition of conduction of heat
- Causes of conduction of heat: (i) Vibrations of atoms in the metals (ii) motion of free electrons present in the metals.
- Definition of good conductors with examples.
- Definition of bad conductors or heat insulators with examples.
- Differentiate between good conductors and bad conductors.
- Comparison of conducting ability of different metals.
- Conduction in solids, conduction in liquids, conduction in gases.
- Definition of rate of heat flow also write its mathematical form and unit.
- Factors of rate of heat flow.
- Definition of thermal conductivity also write its symbol and explanation.
- Definition of a Convection of heat.
- Definition of radiation of heat and also write its cause.
- Differentiate between conductors Convection and radiation.
- Definition of radiation of heat
- Why white clothes are preferred wearing in summer? explain briefly.
- Why is the freezer compartment kept at the top of a refrigerator? explain briefly.
- A black car standing in the sun warms up more quickly than other. why?
- Why a floor feels colder than to bare feet than a carpeted floor?
- How woolen sweaters keep us warm in winter?
- In certain places, the birds are fly for hours without flapping their wings. Explain.
- Good-quality thermos bottle is double walled and evacuated between these walls, and the internal surfaces are like mirrors with a silver coating. How does this configuration combat heat loss from all three transfer methods and keep the bottle's contents your coffee hot?
- A piece of wood lying in the sun absorbs more heat than a piece of a Shiny metals. Yet the metals fields hotter than the wood when you pick it up. explain.
- Some pot handles remain cool during cooking while others become unpleasantly hot. What determines which handles remain cool and which became hot?
- When sunlight warms the land beside a cool body of water, a breeze begins to blow from the water towards the land. Explain.
- Solved Numerical of the exercise Ch 9 Phy Class 9.
- A person's body is covered with 1.6 m² of wool clothing. The thickness of wool is 2.0×10^-3. The temperature at the outside surface of the wool is 11°C, and the skin temperature is 36°C. How much heat per second does the person lose due to conduction? Thermal conductivity of wool is k= 0.04Wm¹K¹.
- The external wall of a brick house has an area of 16m² and thickness 0.3m. The temperatures inside and outside the house are respectively 20°C and 0°C. Calculate the rate of heat loss through the wall? Thermal conductivity of bricks is k= 0.84Wm²¹K.
- Window glass has thermal conductivity of 0.8Wm²¹K¹. Calculate the rate at which heat is conducted through a window of area 2.0mm² and thickness 4.0mm. The temperature inside an air-conditioned room is 20 °C. The outdoors temperature is 35°C.