PHYSICS 5B Lecture 7: Physics 7
How much heat Is needed to raise 1°C In asubstance ?
*depend on the mass of the material
*
depend
on what material
Introduce
Specific heat Cv
Q= MxCvxot
=mcv
(Tt -Ti)
unit of G:Si =¥k ,Concential :5¥
Cv in general is Tdependent .
:dQ✓= MG (T)dT
Cr Econstant
e± Cr =4190 (51kg .k)for water
or G= Icall g. c
-Practical Heat Transfer Problem :Calorimetry
↳Figuring out what Is plus and what Is
.
minus
ex :place anot iron rod into acold water
Qcoid =-Q#+
heat in Ct )
,heat out C- )
t
heat gain by THeat lost by
The cold system the hot system
e± :An aluminum calorimeter with amass of 100g contains 250g of water .The calorimeter and water are In thermal
equilibrium at 10°C .Two metabolic blocks are placed into The water .One Is a50g piece of copper at 80°C .
The other block has amass of 285g and originally at atemperature of 100°C .The entire system
Stabilizes at aTemperature of 20°C
(a) Determine the specific heat of the unknown sample
(b) Guess The material of the unknown
*a÷;Ei⇒L¥¥s
t.MU#io09
final
initial
Calorimeter : to measure heat
Qc old
' -
-Qheut
Miho 4h00 Thao +Mm (
a,OTA,
=-Mcu C(u0[u -Mx C×0T×
[asog .'g# +(oo .94%0)(20 -ioj .
.[50g .34,50 (20 .so )-285g .↳Cao -iooj )
Solve for Cx
Cx =0.107 call g. (=448 J/kg .K
.:Likely to be Iron ,but we can't be 100% sure
↳using table 12.4 (specific heats of solids and liquids .)
