Page 14 - Q & A STPM 2022 Physics

Physics Semester 1 STPM Chapter 1 Physical Quantities and Units
Question 5

(a) By reference to ideal gas equation, PV = nRT where
P = pressure of the gas
V = volume of the gas
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n = number of moles
R = molar gas constant
T = temperature of the gas
Express the unit of R in terms of J, mol and K.
(b) Some real gases obey the equation Semester
(p + a )(V – b) = RT.
V 2 m
m
Where V is the molar volume of the gas. Determine the units of a and b in 1
m
base units.

Answer:
(a) PV = nRT

PV
R =
nT
(N m )(m )
3
–2
unit of R =
mol. K
N m
–1
= = J mol K –1
mol. K
(b) unit of a = unit of pressure, P
V m 2
a = Pa
3
–1 2
(m mol )
∴ unit of a = Pa m mol –2
6
Unit of b = unit of V m
∴ = m mol –1
3

Exam Tips
Exam Tips
Unit of work done
N m = J

5

01 STPM Q&A PHY T1.indd 5 17/02/2022 10:03 AM