Heat (Part 3) class 7


Heat

Q. What do you understand by the term least count? Write the least count of of both clinical thermometer and laboratory thermometer.
Ans. Least count means the minimum value that one can measure accurately on the given scale.
The value of one small division present between a unit of main division on the thermometer scale is called its least count.

Least count of clinical thermometer 
  • in °C = 1/10 = 0.1°C 
  • in °F = 2/10 = 0.2°F

 Least count of laboratory thermometer 
  • in °C = 10/10 = 1°C
Q. Write the features of clinical thermometer.
Ans. The features of clinical thermometer are:
  • The thermometer that is specifically designed to measure our body temperature is called Clinical thermometer (Doctor's thermometer).
  • A clinical thermometer consists of a long, narrow, uniform glass tube. It has a bulb at one end. This bulb contains mercury. Outside the bulb, a small shining thread of mercury can be seen.
  • A clinical thermometer reads temperature from 35°C to 42°C. There is another scale with the range 94°F to 108°F.
  • A clinical thermometer has a kink which prevents the back flow of the mercury into the thermometer bulb when the thermometer bulb is removed from the mouth of a patient.

Q. Write the features of Laboratory thermometer.
Ans. The features of Laboratory thermometer are: 
  • A laboratory thermometer is used for measuring the temperature of objects in a science laboratory.
  • A laboratory thermometer consists of a long, narrow, uniform glass tube. It has a bulb at one end. This bulb contains mercury. Outside the bulb, a small shining thread of mercury can be seen.
  • The range of a laboratory thermometer is generally from (–10°C to 110°C).
  • There is no kink in laboratory thermometer, so as soon as we take the thermometer out of the object, the level of mercury begins to fall. This means that the temperature must be read while the thermometer is in object.
Q. Write some precautions to be observed while reading a clinical thermometer.
Ans. Precautions to be observed while reading a clinical thermometer are:
  • Thermometer should be washed before and after use, preferably with an antiseptic solution.
  • Before use ensure that the mercury level is below 35°C.
  • Read the thermometer keeping the level of mercury along the line of sight.
  • Handle the thermometer with care. If it hits against some hard object, it can break.
  • Don’t hold the thermometer by the bulb while reading it.
Q. Write some precautions to be observed while reading a laboratory thermometer.
Ans. Precautions to be observed while reading a laboratory thermometer are: 
  • Read the thermometer keeping the level of mercury along the line of sight.
  • Handle the thermometer with care. If it hits against some hard object, it can break.
  • Don’t hold the thermometer by the bulb while reading it.
  • It should be kept upright not tilted.
  • Bulb should be surrounded from all sides by the substance of which the temperature is to be measured.
  • The bulb should not touch the surface of the container.
Q. What is the normal human body temperature?
Ans. The normal temperature of human body is 37°C or 98.6 °F.

Q. Boojho got a naughty idea. He wanted to measure the temperature of hot milk using a clinical thermometer.  Paheli stopped him from doing so.  What do you think, why did Paheli stop him from doing so?
Ans. The given situation shows that Paheli knows that the clinical thermometer is specifically designed to measure the temperature of human body only as the temperature of human body normally does not go below 35°C or above 42°C. That is the reason that this thermometer has the range 35°C to 42°C.
Doing such activities of measuring the temperature of hot milk, keeping the thermometer in the sun or near a flame etc can lead to the breaking of clinical thermometer.
Q. Why can't we use laboratory thermometer to measure body temperature?
Ans. Laboratory thermometers do not have a kink like clinical thermometers, so by the time we will be taking it out of our mouth to measure the temperature, the level of mercury will start falling down and hence, we will not be getting an appropriate value of temperature.
Also the least count of laboratory thermometers is higher than clinical thermometers. Hence, inappropriate to measure the human body temperature accurately.




  


  

                                                  

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