Heat || Temperature || Thermometer 

1. What is heat? Write its SI unit. 

Ans: Heat is a form of energy which gives the sensation of warmth. It's SI unit is Joule.

 

2. Which instrument is used to measure heat of a body? 

Ans: Calorimeter is used to measure the heat of a body.

 

3. We feel cold when we touch an ice, why? 

Ans: As we know that heat always flows from hotter body to colder body. When we touch the ice, heat from our body flows towards ice and we feel cold.

 

4. What is temperature? Write its SI unit. 

Ans: The degree of hotness and coldness of a body is known as temperature. Its SI unit is Kelvin (K).

 

5. Which instrument is used to measure temperature of a substance? 

Ans: Thermometer is used to measure temperature of a substance.

 

6. Write any three difference between heat and temperature.(2073 Jhapa) 

Ans:

S.No	Heat	Temperature
1	Heat is a form of energy which gives the sensation of wormth.	It is the hotness and coldness of a body.
2	It is cause.	It is an effect.
3	Its SI unit is Joule.	Its SI unit is Kelvin.

 

7. What is thermometer? 

Ans: An instrument or device which is used for measuring temperature of a body is called thermometer.

 

8. What do you understand by thermometric liquid? Mention two examples.

Ans: The liquid which is filled inside the bulb of thermometer is called thermometric liquid. Mercury and Alcohol are the two thermometric liquid.

 

9. On which principle, thermometer is based? 

Ans: The thermometer is based on the principle that the liquid expands on heating and contracs on cooling.

 

10. Mention the types of thermometer. 

Ans: The following are the different types of thermometer;

§  Clinical thermometer

§  Maximum-minimum thermometer

§  Laboratory thermometer

 

11. What is clinical thermometer? 

Ans: The thermometer which is uswed to measure human body temperature is called clinical thermometer.

 

12. The clinical thermometer has constriction, why? 

Ans: The clinical thermometer has constriction in order to stop the immediate back flow of mercury after removing thermometer from body part. 

OR 

The clinical thermometer has constriction because it allows mercury to rise up in capillary tube when bulb is in contact with body but does not allow to fall back into the bulb after removing the thermometer from body part. Thus, due to presence of constriction, the temperature of human body can be taken easily and accurately.

 

13. What is the range of temperature in clinical thermometer? 

Ans: Clinical thermometer scale ranges from 35^o to 42^oC or, 94^oF to 108^oF.

 

14. What is our normal body temperature? 

Ans: Our normal body temperature is 37^o or 98.6^oF.

 

15. What is maximum-minimum thermometer? 

Ans: The thermometer that is used to measure the maximum and minimum atmospheric temperature of twenty four hours of a particular place is called maximum and minimum thermometer.

 

16. The wall of bulb is made thin in laboratory thermometer, why? 

Ans: The wall of bulb is made thin in laboratory thermometer because if the wall of bulb is made thick, it cannot respond quickly to the change in temperature as glass is poor conductor of heat so that reading may not be exact.

 

17. State any four difference difference between simple thermometer and clinical thermometer. 

Ans:

S.No	Simple Thermometer	Clinical Thermometer
1	Its temperature ranges from -10oC.	Its temperature ranges from 32oC to 42C.
2	It has not kink on capillary.	It has kink on caoillary.
3	Its stem isncylinderical.	Its stem is prismatic shape..
4	Simply it has celsius scale.	It has both celsius and fhrenheit scale.

 

18. Why mercury is used as thermometric liquid? 

Ans: Mercury is used as thermometric liquid due to the following reasons;

§  Mercury is good conductor of heat.

§  It is shiny and opaque.

§  It does not stick to the inner wall of capillary tube.

§  It can measure from - 39^oC.

 

19. Mercury thermometer cannot be used in very cold region, why? 

Ans: Mercury thermometer cannot be used in very cold region because freezing point of mercury is - 39^oC and below this temperature it cannot measure.

 

20. List the advantages of alcohol used as thermometric liquid. 

Ans:The following are the advantages of alcohol;

§  Its freezing point is -117^oC so it can be used at very cold places.

§  Its expansion rate is six times more than that of mercury.

§  It is cheaper than mercury.

 

21. Write any three drawbacks of alcohol as thermometric liquid.

  Ans:The following are the disadvantages/drawbacks of alcohol;

§  It is bad conductor of heat.

§  It has not uniform rate of expansion.

§  It sticks on the inner wall of capillary tube.

 

22. Why is water not used in thermometer? 

Ans: Water is not used in thermometer because water has not uniform rate of expansion and it vaporizes easily when temperature increases that makes difficult on reading.

 

23. Why are upper fixed point and lower fixed point? 

Ans: The upper fixed point is the temperature of steam produced from the pure boiling water at the standard atmospheric pressure. The lower fixed point is the temperature of melting pure ice at the standard atmospheric pressure.

 

24. Write the relationship between Celsius, Fahrenheit and kelvin scale. 

Ans: The relationship between Celsius, Fahrenheit and kelvin scale are; 

(C-0)/100 = (F-32)/180 = (K - 273)/100

 

25. Distinguish between Celsius and Fahrenheit scale. 

Ans:

S.No	Celsius Scale	Fahrenheit Scale
1	Its lower point is 0oC and upper point is 100oC.	Its lower point is 32oF and upper point is 212oF.
2	The scale between melting point and boiling point is divided into 100 equal parts.	The scale between melting point and boiling point is divided into 180 equal parts.

 

26. It is suitable to wear white clothes in summer, why? 

Ans: During summer, solar heat is more and when white clothes are used they reflect almost all light and heat, which makes the body cool. So, white clothes are suitable on summer.

 

27. Black clothes are suitable on winter, why? 

Ans: Balck clothes are suitable on winter because it is a good absorber of heat which makes our body warm.

 

 

Numerical Problems:

1. Convert 37^oC into Fahrenheit scale. 

Ans: We know that,

 (C-0)/100 = (F-32)/180 

or, 37/100 = (F-32)/180 

or, (37x180)/100 = F-32 

or, 6660/100 = F-32 

or, 66.6 = F-32

 or F = 66.6 + 32 

Therefore F = 98.6^oF.

 

2. Convert 212^oF into ^oC. 

Ans: We know that, 

(C-0)/100 = (F-32)/180 

(C-0)/100 = (212-32)/180 

(C-0)/100 = 180/180 

(C-0)/100 = 1 

 (C-0) = 1 * 100 

 C-0 = 100 

C = 100 

Therefore, 212^oF is equal to 100^oC.

 

3. Convert 18^oC into Kelvin scale. 

Ans: We know that, 

(C-0)/100 = (K - 273)/100 

 (18-0)/100 = (K-273)/100 

18/100 = (K-273)/100 

(18*100)/100 = K - 273 

18 = K - 273 

K = 18 + 273 

K = 291 

 Therefore, 18^oC is equal to 291 Kelvin scale.

 

 

BLE Question Solved

1. Write the SI unit of heat and temperature. The shape of thermometer is made prismatic. Why? (2073 Chitwan) 

Ans: The SI unit of heat is Joule and the SI unit of temperature is Kelvin (K). The shape of clinical thermometer is made prismatic instead of cylindrical because prismatic glass magnifies the image of capillary tube that makes easy to observe.

 

2.Calculate the temperature at which both Celsius scale and Fahrenheit scale show the same reading. (2073 Bhaktapur) 

Ans: Suppose x be the temperature where celsius and fahrenheit scale coincide. 

Them, 

(C-0)/100 = (F-32)/180 

 or, x/100 = (x - 32)/180 

 or, (x/100) * 180 = x - 32 

 or, 1.8x = x - 32 

 or, 1.8x - x = -32 

 or, 0.8x = - 32 

or x = -32/0.8 

 or, x = -40 

Hence, -40^oC = -40^oF.  

At -40^o. Celsius and Fahrenheit scale coincide.

 

3. Alcohol thermometer can not be used to measure the temperature of boiling water, why? (2073 Kaski)

  Ans: The boiling point of alcohol is 78^oC while that of water is 100^oC. So, above 78^oC alcohol alcohol vaporizes and cannot measure temperature of boiling water.