HERMAL

187

EXPERIMENT 6
OBJECTIVE

Tostudythe,relationship between the temperature ofa hot body and time

hinga
cooling curve. by plot.
APPARATUS
Newton's law of cooling apparatus (a thin-walled copper
oable walledenclosure), two thermometers, clamp and stand, calorimeter
stop suspended in a
clock/watch.
THEORY
Eom Newton's law of cooling,
Rate of cooling Difference of temperature of body and surrounding provided the tem-
nerature diference should not exceed by 30°C.
dQ
dt
(T- T)
Eor a body of mass m, specific heat s, temperature T kept in suTounding of temperature To.
Q= msT
Then
dQ dT
Rate of cooling, dt
= ms
dt

dT
Hence, ms oc (T- T)
dt

dT (. ms = constant)
<(T-T)
dt
(T- T) decreases, hence rate of fall of temperature
decreases,
AS time increase, T

must also decrease.

DIAGRAM (Fig. 15.01)

enclo0sure
PROCEDURE
1. Fill
(Stepwise)
between double wall
of the enclOsure with water and put the
the space 80°C.
on a laboratory table. heated to about it with
2. Fill the calorimeter two-third with water
with a stirrer in it. Cover
along
3. Suspend the calorimeter inside the enclosure
water andthe other in
a wooden lid having ahole in its middie.
thermometer in enclosure
4. Suspend from clamp and stand, one
calorimeter water.
5. Note least count of the thermometers. least count.
6. Set the stop clock/watch at zero and note its
188

Thermometer
Clamp
Stirrer
Lid
Calorimeter

Water
Double
Stand walled
enclosure

Fig. 15.01. Newton's law of cooling apparatus.

7. Note temperature (T,)of water in enclosure.
8. Start stirring the water in calorimeter to make it cool uniformly.
9. Just when calorimeter water has some convenient temperature reading say 700,
note it and start the stop clock/watch.
10. Continue stirring and note temperature after every one minute. The temperatu
falls quickly in the beginning.
11 Note enclosure water temperature after every five
minutes.
12. When fall of temperature becomes slow note temperature at interval of two mimu
for 10 minutes and then at interval of 5
minutes.
13. Stop when fall of temperature
becomes very slow.
14. Record your
observationsas given ahead.
OBSERVATIONS
Least count of enclosure water thermometer °C
Least count of
Least count of
calorimeter water thermometer °C
stop clock/watch
*... S.
RERMA
R LA

and temperature
for
time
Fble Timeforcooling Temperature of Temperature of Difference
mt) water in calorimeter twater in enclosure of temperatiure
TC) T, (°C) T-T(C)
(2) (3) (4) (5)
70 30 40

1
68 38
66 36

64 34

62 32
4
61 30 31
5
60 30
6
59 29
7
28
58
26
56
30 24
54
10
23
53
12 21
12
51
13
14 19
49
16 16
14.
46
15 18 14
30
44
16 20 12
30
42
17. 25
30
38
18. 30 6
30
36 5
19. 35
30
35 4
20. 40 30
34
21 45

aboveare as Sample. )
Note. The ideal observations given
then take its
CALCULATIONS enclosure will be found to remain
same. If not
1. Temperature of water in
5 of the table.
mean as To: and record it in column along
2. Find temperature difference (T- T)
temperature T(olumn 3), taking t called
2) and
(column 15.02, It is Fig.
t
Plot a graph between time The as shown in
graph comes to be
X-axisand T along Y-axis.
cooling curve' of the liquid.
 Graph between time and termperature
PHYSICH
Scale:
X-axis :1 om 5 minutes of t
Y-axis : t Gm # 5° Cof T

704
C 85
in COOLING CUAVE
(t) 60
Temperature

50

45

40

35

30
O0 5 10 15 20 25 30 35 40 45
Time (t) in minute

Fig. 15.02. Graph between time (t) and temperature ()-cooling curve.
RESULT
The temperature falls quickly in the beginning and then slowly as
ture goes on decreasing. difference of temper.
This is an agreement with Newton's law of cooling.
PRECAUTIONS (to be taken)
1 Double-walled enclosure should be
used to maintain surrounding at a
perature. constant tem
2.
Stirring should remain continuous for uniform
cooling.
SOURCESOF ERROR
1. Surrounding
temperature may change.