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risingabove
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Homework Statement
If a copper kettle has a base of thickness 2.0mm and an area 3.0 x 10-2 m2 estimate the steady difference in temperature between the inner and outer surface of the base which
must be maintained to enable enough heat too pass through so that the temperature of 1 kg of water
rises of 0.25 K/s assume that there are no heat losses.
(ii) After reaching the temperature of 373K the water is allowed to boil under the same conditions for 120 seconds and the mass of water remaining in the kettle is 0.948kg.
Deduce a value for the specific latent heat of vaporization of water ( neglecting condensation of the steam in the kettle)
Homework Equations
Thermal conductivity of copper 3.8 x 102 W/m/C
Specific Heat Capacity of water 4.0 x 103 J/kg/K
Equations used
dQ/dt = kA(dΘ/dx)
where dQ/dt = rate of flow of heat
K = Thermal Conductivity
A = Area
dΘ = Change in Temperature
dx = Thickness
whereby dΘ/dx = Temperature gradient
Q = mCT
Where Q = Heat require
m = Mass of substance
C = Specific heat capacity
T = Temperature
Q= mL
Where Q = Heat Require
m = Mass
L = Latent Heat
The Attempt at a Solution
Firstly i used the specific heat capacity equation to find the rate of flow of heat
Q = 1 (4.2 x 103 J/kg/K ) 0.25 K/s
= 1050 J/s
Using the above answer i substitute it into the equation for thermal conductivity
1050 = 3.8 x 102 W/m/C (3.0 x 10-2 m2 )(dΘ/0.002m)
by simple calculations my answer = 0.18 degrees
Part (ii)
I am abit lost as to where to go from here... but I am thinking i will have to multiply 120 seconds by 0.25K/s which = 30 K/s
and used the 30K/s in the specific heat capacity equation ...( but I am thinking that doesn't make any sense)
By using the 373k and substituting it into the heat capacity equation
Q = 1(4.2 x 103 J/kg/K)373
= 1566600J
and using the answer above in the Latent heat of vaporization equation
1566600 = 0.948L
L = 1.6 x 106 J/kg/K
This seems wrong tho...
By the way is my answer correct for Part (i) ??
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