Week 2 – SS1 Second Term Physics Notes

 WEEK TWO
TOPIC: Thermometer and Its Type. Evaporation and Boiling
CONTENT

• Thermometer and Their Thermometric Substance
  
• Fixed Point of Thermometer
  
• Evaporation and Boiling
  

 Thermometer and Their Thermometric Substance
Thermometric substances are substances which changes in proportion to temperature.

 ADVANTAGES OF MERCURY AS A THERMOMETRIC SUBSTANCE

1. Mercury does not wet glass
2. Mercury response quickly to slight change in temperature
3. The liquid does not vaporize easily
4. Mercury is opaque Hence, it can be seen easily
5. It has a regular or uniform expansion.

    DISADVANTAGES

6. Mercury is expensive
7. Mercury can not be used to measure very low temperature because it’s freezing

   point – 39˚C

    ADVANTAGES OF ALCOHOL AS A THERMOMETRIC SUBSTANCE
   

8. Alcohol is less expensive than mercury
9. It has larger expansion on heating than mercury (it expands 6 times more than

   mercury).

10. It can be used to measure very low temperature.

     DISADVANTAGES
    

11. It is not opaque and so most be colored
12. It vaporizes easily
13. It wet glass
14. It has an irregular expansion
15. It has low boiling point of 78˚C

     CONSTANT VOLUME GAS THERMOMETER
    

16. It gives more accurate measurement of temperature than any other

    thermometer

17. It is very sensitive and can measure wider range of temperature

     DISADVANTAGES

18. It is very expensive and so require handling with special care
19. It is very cumbersome

     EVALUATION
    

    1. What advantage does a constant volume gas thermometer has over other

       thermometers?

    2. Mention five types of thermometer, their thermometric substance and physical property.

     FIXED POINT OF THERMOMETER
    Fixed temperature point are two reference temperature (usually upper and lower fix point) chosen, when preparing a scale for reading temperatures.

     Upper Fixed Point: is the temperature of steam from pure water at the normal atmospheric pressure.

     Lower Fixed Point: is the temperature of mixture of pure ice and water at normal pressure.
    Fundamental Intervals: is the interval between the upper and lower fixed point.
    100⁰C                373K                 212⁰F        

     
     
     
     
         0⁰C                273K                    32⁰F
    Celsius Scale             Kelvin Scale            Farenheit Scale

     REASON WHY WATER IS NOT USED AS A THERMOMETRIC
    

20. Water wet glass
21. They are colour less
22. It does not expand uniformly
23. It has small range of expansion (0˚C to 100˚C)

     CLINICAL THERMOMETER
    It is used for measuring the temperature of human body. The body temperature ranges from (35˚C to 45˚C). It is not advisable to sterilize a clinical thermometer in boiling water because a short range of 35˚C to 43˚C which shall result to

    1. Cracking or breaking of thermometer due to excessive expansion of the mercury.
    2. Malfunction of the thermometer due to over expansion of the capillary tube and the mercury inside the bulb.

     

     Evaporation and Boiling
    Evaporation is the process where a liquid turns into vapor below its boiling point. Evaporation takes place at all temperature. Wind assist evaporation.
    Boling is the change from liquid to vapor at the boiling point. It occurs throughout the entire volume of the liquid. Wind has no effect on boiling.

     EVALUATION
    

24. Why is water not used as a thermometric substance?
25. Differentiate between evaporation and boiling.

     Reading Assignment
    www.google.com (click on google search, type “temperature & its measurement”, click on search) and New School Physics pg 202 – 209

     WEEKEND ASSIGNMENT
    

    1. The clinical thermometer is characterized by having a A.wide range of temperature B. wide bore C. long stem D. constriction
    2. A short response time is obtained in a liquid – in-glass thermometer when the A. bulb is large and thick walled B. bulb is small and thin walled C. stem is long and thin D.bulb is thin walled and the liquid is a good conductor of heat.
    3. Change in volume with temperature is the physical propety of ………. thermometer A. constant volume gas B. liquid-in-glass C. resistant

       D. thermoelectric

    4. Convert 27⁰C to kelvin A. 290K B. 300K C. 300⁰C D. 310K
    5. The following are units of temperature except A. kelvin B. degree Celsius

       C. ampere D. Fahrenheit

     THEORY
    

    1. Mention five types of thermometer, their thermometric substance and physical property.
    2. Why is it not advisable to sterilize a clinical thermometer in boiling water?