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.
(a) Iron rim, to be put on a cart wheel, is designed to have a (slightly) smaller diameter than that of the wheel. When this rim is heated, it becomes ‘red-hot’, expands, and slips on to the wheel easily. When it is cooled, it contracts and grips the wheel firmly.
(b) A clinical thermometer has a slight bend, or kink, in its capillary tube because this ‘kink’ helps to maintain the level of mercury that raised due to temperature so that reading can be taken accurately.
(c) A quilt makes use of the bad conductivity of air. It traps a layer of air between themselves and our body and does not allow our body heat to escape out easily. Such trapping of air is much better in a new quilt than in an old one because when the quilt gets older, the air spacing of the cotton or wool gets compressed.
(d) A brass tumbler feels much cooler than a wooden tray on a chilly day because brass is good conductor of heat. When we touch it, heat is conducted from the body to the brass tumbler easily and temp. of our body reduces to a lower value. Thus, we feel cooler. on the other hand, wood is a poor conductor of heat and very little heat is transfer to the wooden tray when we touch it. Thus, we don’t feel cooler.
(e) The bottom of cooking utensils is often kept black. This enables the utensils to better absorb the heat of the flame.