CHAPTER – 11 Constant volume gas thermometer
THERMAL PROPERTIES OF Principle: -
MATTER
We have PV nRT , for a low density
Heat and Temperature gas.
Heat is the form of energy, which is i.e., PV α T
transferred from one body to
another because of their If volume is kept constant P α T
temperature difference.
I.e., when temperature increases,
Temperature is the degree of hotness pressure also increases.
of a body. In constant volume gas thermometers
SI unit of heat is joule (J) temperature is read in terms of
pressure.
SI unit of temperature is Kelvin (K)
Common units of temperature
Measurement of temperature
The commonly used units are Degree
The device used to measure Celsius, Kelvin and Fahrenheit.
temperature is called thermometer.
Formulae for unit conversion
There are two types of thermometers
tK = tC+ 273
i. Liquid – in –glass type
thermometers. 9
t F t C 32
ii. Constant volume gas thermometers. 5
Liquid – in –glass type Problem1: -Convert the ice point
thermometers (00C) and the steam point (1000C) into
Kelvin and Fahrenheit scales.
Principle: - Thermal expansion of
liquids. I.e., when temperature Soln: -
increases, volume of liquids increases.
Ice point (00 C) Steam point (1000C)
Commonly used liquids: - Mercury, tC 0 tC 1000 C
Alcohol. t K 0 273 273K tK 100 273 373K
9 9
Question1: - Why mercury is used in t F 0 32 320 F t F 100 32
5 5
thermometer?
=180 32
Ans: - Mercury is used because of 2120 F
the following properties of it. Problem2: Temperature of a normal
human body is 98.60F. What is the
i. It has high thermal expansivity. corresponding temperature shown in the
ii. It has a shining surface. Celsius scale?
iii. It does not wet glass.
Ans:
SAJU K JOHN, M.Sc. Physics, NET, Doctoral Research Fellow at NIT Calicut 1
, A low density gas obeys the
following two equations :
1
V and V T
P
So if we combine these
equations,
T
V PV T
P
Boyle’s law PV nRT,
Boyle’s law states that ‘at constant PV
or Cons tan t
temperature, the volume of a given T
mass of gas is inversely P1V1 P2 V2
proportional to pressure’. T1 T2
Where n is the no. of moles (n ) and
1 R is the universa l g as cons tan t.
V PV cons tan t
P
R 8.31 Jmol 1K 1 .
P1 V1 P2 V2
The equation PV nRT is known as
Charles’ Law idea l g as equation and is obeyed by
low density gases.
Charles’s law states that ‘at constant
pressure, the volume of a given Problem3: The volume temperature
mass of gas is directly proportional graph of certain amount of perfect gas
to absolute temperature’. at two pressures P1 and P2 are shown.
Which pressure is larger P1 or P2?
V
V T cons tan t
T
V1 V2
T1 T2
Ideal gas equation
Ans:
SAJU K JOHN, M.Sc. Physics, NET, Doctoral Research Fellow at NIT Calicut 2
THERMAL PROPERTIES OF Principle: -
MATTER
We have PV nRT , for a low density
Heat and Temperature gas.
Heat is the form of energy, which is i.e., PV α T
transferred from one body to
another because of their If volume is kept constant P α T
temperature difference.
I.e., when temperature increases,
Temperature is the degree of hotness pressure also increases.
of a body. In constant volume gas thermometers
SI unit of heat is joule (J) temperature is read in terms of
pressure.
SI unit of temperature is Kelvin (K)
Common units of temperature
Measurement of temperature
The commonly used units are Degree
The device used to measure Celsius, Kelvin and Fahrenheit.
temperature is called thermometer.
Formulae for unit conversion
There are two types of thermometers
tK = tC+ 273
i. Liquid – in –glass type
thermometers. 9
t F t C 32
ii. Constant volume gas thermometers. 5
Liquid – in –glass type Problem1: -Convert the ice point
thermometers (00C) and the steam point (1000C) into
Kelvin and Fahrenheit scales.
Principle: - Thermal expansion of
liquids. I.e., when temperature Soln: -
increases, volume of liquids increases.
Ice point (00 C) Steam point (1000C)
Commonly used liquids: - Mercury, tC 0 tC 1000 C
Alcohol. t K 0 273 273K tK 100 273 373K
9 9
Question1: - Why mercury is used in t F 0 32 320 F t F 100 32
5 5
thermometer?
=180 32
Ans: - Mercury is used because of 2120 F
the following properties of it. Problem2: Temperature of a normal
human body is 98.60F. What is the
i. It has high thermal expansivity. corresponding temperature shown in the
ii. It has a shining surface. Celsius scale?
iii. It does not wet glass.
Ans:
SAJU K JOHN, M.Sc. Physics, NET, Doctoral Research Fellow at NIT Calicut 1
, A low density gas obeys the
following two equations :
1
V and V T
P
So if we combine these
equations,
T
V PV T
P
Boyle’s law PV nRT,
Boyle’s law states that ‘at constant PV
or Cons tan t
temperature, the volume of a given T
mass of gas is inversely P1V1 P2 V2
proportional to pressure’. T1 T2
Where n is the no. of moles (n ) and
1 R is the universa l g as cons tan t.
V PV cons tan t
P
R 8.31 Jmol 1K 1 .
P1 V1 P2 V2
The equation PV nRT is known as
Charles’ Law idea l g as equation and is obeyed by
low density gases.
Charles’s law states that ‘at constant
pressure, the volume of a given Problem3: The volume temperature
mass of gas is directly proportional graph of certain amount of perfect gas
to absolute temperature’. at two pressures P1 and P2 are shown.
Which pressure is larger P1 or P2?
V
V T cons tan t
T
V1 V2
T1 T2
Ideal gas equation
Ans:
SAJU K JOHN, M.Sc. Physics, NET, Doctoral Research Fellow at NIT Calicut 2
