Solved MCQs | Chapter 9 | Transfer of Heat | Physics 9th | KPK Textbook Board, Peshawar | Urdu

Описание: Q. Choose the best possible option.
Which of the following is the best heat conductor?
(a) aluminum (b) tin (c) iron (d) copper
Identical cubes of following materials are kept in a room at the same temperature, which will feel coldest by touching them?
(a) Wood (b) Glass (c) Iron (d) Styrofoam
The transfer of heat by convection is smallest in
(a) solids (b) liquids (c) gases (d) none
One way that heat is transferred from place to place inside the human body is by the flow of blood. Which one of the following heat transfer processes best describes this action of the blood?
(a) convection (b) conduction (c) radiation (d) none
The best absorber of radiation is a body whose surface is
(a) white (b) grey (c) dull black (d) highly polished
The mode of transfer of heat which does not require material medium is called
(a) convection (b) conduction (c) radiation (d) none
Which of the following has the highest thermal conductivity
(a) water (b) wood (c) wool (d) air
The temperature at which a body is not radiating any heat is
(a) 0℃ (b) 0℉ (c) 0K (d) all of these
The electrons that are free to move through the metal called
(a) lose electrons (b) free electrons (c) conduction electrons (d) holes
Q. Give a short response to the following questions
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 any other. Why?
Why a tile floor feels colder to bare feet than a carpeted floor?
How woolen sweaters keep us warmer in winter?
In certain places, birds can 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 shiny metal. Yet the metal feels 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 become hot?
When sunlight warms the land beside a cool body of water, a breeze begins to blow from the water toward the land. Explain.
Q. Solve the following numerical questions.
A person’s body is covered with 1.6m^2 of wool clothing. The thickness of the wool is 2.0×〖10〗^(-3) m. The temperature at the outside surface of the wool is 11℃, and the skin temperature is 36℃. How much heat per second does the person lose due to conduction? Thermal conductivity of wool is k=0.04Wm^(-1) K^(-1).
The external wall of a brick house has an area of 16m^2 and thickness 0.3m. The temperatures inside and outside the house are respectively 20℃ and 0℃. Calculate the rate of heat loss through the wall. Thermal conductivity of brick is k=0.84Wm^(-1) K^(-1).
Window glass has thermal conductivity of 0.8Wm^(-1) K^(-1). Calculate the rate at which heat is conducted through a window of area 2.0m^2 and thickness 4.0mm. The temperature inside an air-conditioned room is 20℃. The outdoors temperature is 35℃.