Question

Give reasons for the following:
(a) Iron rims are heated red hot before 'fixing them on cart wheels.
(b) A clinical thermometer has a slight bend, or kink, in its capillary tube.
(c) A new quilt is warmer than an old one.
(d) A brass tumbler feels much cooler than a wooden tray on a chilly day.
(e) The bottoms of cooking utensils are often kept black.​

Answer 1

Here u go!

a) The iron ring to be put on the rim of a cart wheel is always of slightly smaller diameter than that of the wheel. When the iron ring is heated to become red hot, it expands and slips on to the wheel easily. When it is cooled, it contracts and grips the wheel firmly.

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b) The kink prevents the mercury in the capillary to fall back into the bulb. So it separates the high temperature mercury and cool temperature mercury and allow the user to take a reading when the thermometer is taken out. The kink prevents the mercury in the capillary to fall back into the bulb.

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c) A new quilt is warmer because the air which is trapped inside the cotton or woollen clothing acts as an insulator and does not allow the transfer of heat. However, when the quilt gets older, the air spacing of the cotton or wool gets compressed.

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d) Thus when we touch brass heat escapes toward the object due to conduction and we feel it much cooler. Answer:we know that, Brass is a good conductor of heat so, brass is much cooler than the wooden tray because,the wooden tray is made up of wood,wood is a good conductor of heat.

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e) The bottoms of cooking utensils often kept black because they observe maximum amount of heat which is necessary for cooking and where as upper part kept shining so that minimum amount of heat is lost.

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Hope it helps :)

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