Page 107 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

Feedback To Activity 3B

3.4 Since the gas is compressed according to the law pV = C, then,
1.4

p 1 V 1 4 . 1 = p 2 V 2 4 . 1

p V  4 . 1 V  p  4 . 1 / 1
 1 =  2  or 2 =  1 


p 2  V 1  V 1  p 2 

from which,

 p  4 . 1 / 1 p

V 2 = V 1   1  = V 4 . 1 1
 p 2  1 p 2

138
= 0.012 x 4 . 1
690
3
= 0.0348 m

3.5 The work done during a polytropic expansion is given by the expression:

p V − p V
W = 1 1 2 2 [larger pV- small pV]
n − 1
In this problem V2 is, as yet, unknown and must therefore be calculated.

Now

n
n
p
V = p 2 V
2
1
1
 p  n / 1

 V = V  1 
1 
2
 p 2 
 2070  . 1 / 1 35
or V2 = 0.014 x  
 207 
3
V2 = 0.077 m
98 | P a g e