Matric Notes Physics 9th Ch 9 Transfer of Heat Short Questions

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Q1. why a wire-gauze is often placed over a burning flame for heating on object?

Ans. A wire gauze is often placed over a burning flame for heating a object. Because wire gauze conducts heat outward form flame a glass beaker can be heated safely o wire gauze because it protects the beaker from the contracted heat of the flame.

Q2. Give three ways in which insulating material can be used to reduce head losses from a houses?

Ans. i) use air filled cavity walls instead of solid bricks walls.

ii) In roof a layer of insulating material like plastic can be used to reduced heat conduction.

iii) Houses with small windows and doors will loss small amount of heat energy.

Q3. why is the freezer compartment kept at the top refrigerator?

Ans. The freezer compartment of a refrigerator is kept at top because it cools the air of surrounding and makes it denser compare to the air of bottom the cool air moves downward while warmer air moves upward, where it is cooled.

Q4. why does thermal radiations pass more easily into a green house than out of it?

Ans. The heat is transmitted into a green house in the form of high frequency from sun these radiation are emitted back inside the green house in the form of low frequency. Which cannot escaped from a glass block and are trapped inside.

Q5. How heat losses are reduced in a thermos flask?

Ans. A thermos flask consists of doubled walled glass vessel silvered on the inner side. The silvered surface reflects back all radiant heat trying to leave vessel by radiations. The space b/w two walls is highly evacuated to prevent convection. The glass being a poor conductor, minimize the conduction of heat.

Q6. How the interior of a car parked in the hot sum warms easily?

Ans. Heat is transmitted into a car in the form of high frequency from sun these are reflected inside and losses some energy and appears as low frequency radiation which cannot escaped car and are trapped back.

Q7. A black car, standing in the sun warms up more quickly than any other why?

Ans. A black car standing in the sun warms up more quickly than any other because the black surface is a good absorber of heat radiator than any other surface.

Q8. How air filled cavity walls keep a hose warmer in winter than a solid brick wall?

Ans. the air is a bad conductor of heat so an air filled wall keep a house warmer because It stops the flow of heat from hose to outside. It stops the flow of heat from house to outside.

Q9. why a tile floor feels colder to bare feet than carpeted floor?

Ans. A carpet is bad conductor of heat as compare to tile floor when a bore foot is put on the floor more heat is lost by the foot which is absorbed by tile floor and as a result we feel cool. If we put the foot on carpet floor we feel less cool because tile in this case our feet losses no heat that’ why a floor feels colder to bare feet then a carpet floor.