# Frank Solutions for Chapter 5B Heat: Thermometry Class 9 Physics ICSE

1. What do you mean by temperature?

Temperature is the quantity that tells about the thermal state of a body i.e. the degree of hotness or coldness of a body.

2. Name the instrument used for measuring the temperature of a body.

Thermometer is used for measuring the temperature of a body.

3. What is the principle used in a thermometer?

Thermometer works on the principal that substances expand when heated and contract on cooling.

4. What is meant by the range of a thermometer?

Range of thermometer is the range of temperature which can be measured by thermometer.

5. Name the liquid used in a clinical thermometer.

Mercury is the liquid used in a clinical thermometer

6. What is the usual range of temperature marked on a clinical thermometer?

The usual range of temperature marked on clinical thermometer is 95° F to 110° F.

7. Who designed the first thermometer?

Fahrenheit designed the first thermometer.

8. What do you mean by calibration of a thermometer?

Before constructing a thermometer, we determine lower fixed point and upper fixed point and divide the whole range of thermometer into specific number of equal divisions to provide a scale for measuring the temperatures within a range.

9. What is a clinical thermometer?

The clinical thermometer is specially designed thermometer used to measure the temperature of a human body easily and as accurately as possible.

10. State three properties of a liquid which make it suitable to be used in a thermometer.

Three properties of a liquid which make it suitable to be used in a thermometer are:

1. The substance should have high coefficient of expansion so that it is sensitive to the smallest change in temperature
2. The substance should have uniform expansion all over its entire volume
3. The substance should have minimum specific heat so that it absorbs minimum heat from the body under measurement.

11. State two disadvantages of using mercury as a thermometric liquid.

Two disadvantages of using mercury as a thermometric liquid:

1. It does not have uniform expansion.
2. Mercury is less sensitive than alcohol as its coefficient of expansion is less than alcohol.

12. State three advantages of using mercury in a thermometer liquid.

Three advantages of using mercury as a thermometric liquid:

1. Mercury is good conductors of heat.
2. Mercury have high coefficient of expansion thus is sensitive to the smallest change in temperature.
3. Freezing points is very low and boiling point is high.

13. State two disadvantages of using water as a thermometric liquid.

Water is not used as a thermometric liquid because it has low coefficient of expansion so it is less sensitive to temperature changes. Moreover, it is transparent thus making it difficult to read the thermometer and water evaporates with time thus producing error and also the freezing and boiling points are also low.

14. Express 0°C in Kelvin.

Temperature in Kelvin To K = Temperature in Celsius To C + 273.

To K = 0°C + 273

To K = 273 K.

15. The body temperature of a healthy person is 98.4°F. Find the corresponding temperature on the Celsius scale.

Body temperature of a healthy person is 98.4°F.

We know C/100 = (F - 32)/180.

C = 5/9(F - 32)

⇒ C = 5/9(98.4 - 32)

⇒ C = 5/9 × 66.4

⇒ C = 36.88°C

Temperature of body of healthy man is 36.88°C.

16. The temperature of a body rises through 1°C. What is the corresponding rise on absolute scale?

Absolute scale of temperature is Kelvin scale.

Conversion of temperature from Celsius to Kelvin scale is

Temperature in Kelvin To K = Temperature in Celsius To C + 273.

So a rise of temperature of 1°C in Celsius scale is equal to rise of 1°K in Kelvin scale.

17. Name the temperature scale used in SI system.

Kelvin temperature scale is used in SI system.

18. How is the size of a degree defined on the Celsius scale?

In Celsius scale there are two fixed points namely lower fixed point and upper fixed point at 0°C and 100°C respectively. This range is divided into 100 equal divisions and each part gives 1°C.

19. Convert -15°C on the Fahrenheit scale.

We know C/100 = (F - 32)/180.

C = 5/9(F - 32)

⇒ 9/5C + 32 =F

⇒ F = 9/5C + 32

Temperature given in Celsius = -15°C.

F = 9/5 × (-15) + 32

⇒ F = -27 + 32

⇒ F = 5°F

20. What is absolute zero on the Celsius Scale?

Absolute zero of temperature is 0°K.

Temperature in Kelvin To K = Temperature in Celsius To C + 273.

0°K = C + 273.

⇒ C = -273°C.

Absolute zero of temperature on Celsius scale is -273°C.

21. The temp. of two bodies differ by 19°C. What is the difference on Fahrenheit scale of temperature?

Difference of temperature of two bodies in Celsius scale = 1°C.

We know C/100 = (F - 32)/180.

C = 5/9(F - 32)

⇒ 9/5C + 32 = F

⇒ F = 9/5C + 32.

So, difference of 1° in Celsius scale is equal to the difference of 9/5° in Fahrenheit scale.

Thus, Difference of 1°C of temperature of two bodies in Celsius scale is equal to difference of 1.8° in Fahrenheit scale.

22. Who invented Celsius scale of temperature?

Celsius invented the Celsius scale of temperature.

23. Who invented Fahrenheit scale of temperature?

Fahrenheit invented the Fahrenheit scale of temperature.

24. Name two liquid thermometers that are commonly used.

Mercury, alcohol are commonly used in thermometers.

25. Name two animals which are able to increase their body temperature in summers and decrease their body temperature in winters.

Camel and are two animals which are able to increase their body temperature in summers and decrease their body temperature in winters.

26. Name the CGS unit of heat. Define it.

CGS unit of heat is Joule denoted by J.

1 J is amount of heat required to raise the temperature of a body by 1/4.12°C of temperature.

27. Plot a graph taking °C on the Y-axis and the corresponding °F along the X-axis.

We know C/100 = (F - 32)/180.

C = 5/9(F - 32)

⇒ C = 5/9F - 17.77.

Graph between T° C and T° F is straight line having slope of 5/9 and intercept on Y axis is -17.77.

28. Plot a graph taking °F along the Y-axis and the corresponding °C on the X-axis.

We know C/100 = (F - 32)/180.

C = 5/9(F - 32)

⇒ 9/5C + 32 = F

⇒ F = 9/5C + 32.

Graph between T°F and T°C is straight line having slope of 9/5 and intercept on Y axis is 32.

29. Write the relationship between the Celsius and Fahrenheit scales of temperature.