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www.GOALias.blogspot.comand hot water in mug C. Now dip yourleft hand in mug A and the right handin mug B. After keeping the hands inthe two mugs for 2–3 minutes, put boththe hands simultaneously in mug C(Fig. 4.1). Do both the hands get thesame feeling?Boojho’s confusion shows that wecannot always rely on our sense of touchto decide whether an objectis hot or cold. Sometimesit may deceive us.Then, how do we findout how hot an object reallyis? A reliable measure of thehotness of an object is itstemperature. Temperature ismeasured by a device calledthermometer.4.2Boojho says,“My left handtells me that the water in mugC is hot and the right handtells me that the same wateris cold. What should Iconclude?”4.2 MEASURINGTEMPERATUREHave you seen a thermometer? Recallthat when you or someone else in yourfamily had fever, the temperature wasmeasured by a thermometer. Thethermometer that measures our bodytemperature is called a clinicalthermometer. Hold the thermometer inFig. 4.2 A clinical thermometeryour hand and examine it carefully. Ifyou do not have a thermometer, requesta friend to share it with you. A clinicalthermometer looks like the one shownin Fig. 4.2.A clinical thermometer consists of along, narrow, uniform glass tube. It hasa bulb at one end. This bulb containsmercury. Outside the bulb, a smallshining thread of mercury can be seen.If you do not see the mercury thread,rotate the thermometer a bit till you seeit. You will also find a scale on thethermometer. The scale we use is thecelsius scale, indicated by °C.Boojho wondered which of the two scalesshown in Fig. 4.2 he should read. Paheli toldhim that India has adopted the celsius scaleand we should read that scale. The other scalewith the range 94–108 degrees is theFahrenheit scale (°F). It was in use earlier.A clinical thermometer readstemperature from 35°C to 42°C.Activity 4.2Reading a thermometerLet us learn how to read a thermometer.First, note the temperature differenceindicated between the two bigger marks.Also note down the number of divisions36SCIENCE