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Q4 why laboratory thermometer does not have a kink?

Q5 what precautions will you observe while using a clinical thermometer?

Q6 describe an experiment to show convection currents in a liquids.

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In a clinical thermometer we can see the reading of the thermometer even after removing it from the patient’s body. This is possible because of the kink. The kink breaks the connection between the mercury in the capillary and the bulb containing it at the lower end of the thermometer. This is why we have to shake the thermometer vigorously to bring it back to the lowest level. However, a laboratory thermometer has to measure temperature change continuously. The mercury level has to go up and down continuously. So, there is no kink in a laboratory thermometer.

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1.Ans-Labortary thermometer doesnot have a kink because the temparature of the liquid must be read while the thermometer is in the liquid.since the level of mercury drops as soon as the thermometer is taken out of the liquid.

2.Ans-We should take following precautions while reading a clinical thermometer:-

i)It should be washed before and after using with an anticeptic solution.

ii)We should check or ensures that the mercury level should be 35 degree celsius begore using it.

iii)The reading should be taken while keeping the level of mercury along the line of sight.

iv)We shouldnot hold the thermometer by its bulb while reading it.

v)We should handle the thermometer with care,as it is breakable.

3.Ans-

Convection currents in water may be shown by filling a large spherical flask with water and dropping a single large crystal of potassium permanganate ( KMnO4) to the bottom of it through a length of glass tubing. A finger is placed over the end of the tube, which is then removed, together with the colored water it contains.

 This method of introducing the crystal ensures getting it in the centre and also prevents it from coloring the water before it is required. On heating the bottom of the flask with a very small gas flame an upward current of colored water will ascend from the place where heat is applied. This colored stream reaches the top and spreads out.

After a short time it circulates down the sides of the flask, showing that a convection current has been set up.

Explanation of convection currents

 When a portion of liquid near the bottom of a vessel is heated it expands. Since its mass remains unaltered, it becomes less dense ( you remember that Density = mass / volume ), and therefore rises. Thus a warm convection current moves upwards; for the same reason a cork rises in water or a hydrogen-filled balloon rises in air. In effect, convection is an application of Archimedes' principle. For further illustration please readBalloons and floating bodies.

 If, on the other hand, some liquid in a vessel is heated at the top, the liquid there expands and remains floating on the denser liquid beneath. No convection current is set up, and the only way in which heat can travel downwards under these conditions is by conduction.

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1.Ans-Labortary thermometer doesnot have a kink because the temparature of the liquid must be read while the thermometer is in the liquid.since the level of mercury drops as soon as the thermometer is taken out of the liquid.

2.Ans-We should take following precautions while reading a clinical thermometer:-

i)It should be washed before and after using with an anticeptic solution.

ii)We should check or ensures that the mercury level should be 35 degree celsius begore using it.

iii)The reading should be taken while keeping the level of mercury along the line of sight.

iv)We shouldnot hold the thermometer by its bulb while reading it.

v)We should handle the thermometer with care,as it is breakable.

3.Ans-Convection currents in water may be shown by filling a large spherical flask with water and dropping a single large crystal of potassium permanganate ( KMnO4) to the bottom of it through a length of glass tubing. A finger is placed over the end of the tube, which is then removed, together with the colored water it contains.

This method of introducing the crystal ensures getting it in the centre and also prevents it from coloring the water before it is required. On heating the bottom of the flask with a very small gas flame an upward current of colored water will ascend from the place where heat is applied. This colored stream reaches the top and spreads out.
After a short time it circulates down the sides of the flask, showing that a convection current has been set up.
Explanation of convection currents
 
When a portion of liquid near the bottom of a vessel is heated it expands. Since its mass remains unaltered, it becomes less dense ( you remember that Density = mass / volume ), and therefore rises. Thus a warm convection current moves upwards; for the same reason a cork rises in water or a hydrogen-filled balloon rises in air. In effect, convection is an application of Archimedes ' principle. For further illustration please readBalloons and floating bodies.
If, on the other hand, some liquid in a vessel is heated at the top, the liquid there expands and remains floating on the denser liquid beneath. No convection current is set up, and the only way in which heat can travel downwards under these conditions is by conduction.

 

 
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