My explanation of Thermal Properties!

[Baladya]

Ari Ben Canaan asked me to explain Thermal Properties for him, so i thought i should share it with you too
I m sorry its a bit unorganized but thats the best i could do and i hope it helps u
If you see anyone in need of an explanation, plz send him a link of this topic



THERMAL PROPERTIES


Well first of all know that everything expands when heated. And they all contract when cooled. Water however, contracts when cooled until it reaches 4*C then it becomes to expand when cooled more.

There are diff ways to measure temp:

1-Liquid in Glass (alchohol or mercury)

Thermometrs are characterised by Sensitivity: which is that when a small amount of heat is given to a liquid, it expands a lot. In this case alchohol expands more. Another way to make it more sensitive is to make the bulb big and the narrow glass tube

Another characteristic is Range and it means till what temp can the liquids expand without getting boiled or become solid. For example Mercury has a freezing point of -38 so it would be useless in Antartica cuz it will freeze. Alchohol has a boiling point of 78, so its not good for hot places cuz it will boil easily

Linearity is that the thermometer is correctly calibrated. So if the temp increases to 30*C, the thermometer will show exactly 30
Also accuracy, which pretty much depends on linearity, which means that it should show correct temps. (i dont realy no the diff between accuracy and linearity)

Calibration of the thermometer is by putting it in MELTING ice and marking the point of the liquid. Put it in STEAM and mark it. Then divide it to 100 diff marks

2-Thermocouple can be used to measure too... It is small so it can fit into small areas, and cuz its small so its fast. It can read up to 1000*C so its good for industry. Its digital so it can be read on a remote dial...
I can't find a good pic but this is what it consists of :                \/ -------------------------- --------------------------------
                                                                                                                                                                                                                         |
                                                             (hot conjunction (the object)                                                                                                       V
                                                                                                                                                                                                                         |
                                                                                                            /\ ---------connected to beaker of ice hear) ----------------

Look, the upper wire and the wire under the Voltmeter are made of copper. the one between the ice and hot is made of constantan.


3- Bimetallic strip can measure temp too but u just have to know that it is used in stuff like iron (for clothes). What happens is that when u connected to power, two stripes gets heated, as they get more heated on of them expands more and breaks contact, and so 'cut' a circuit and the heating element stops getting current and just stop

I will tell you more but just lemme study for some time xD

Edit:
Now we will discuss Thermal Capacity:

Thermal Capacity is the amount of heat needed to heat up an object. SPECIFIC heat capacity is: The amount of heat needed to RAISE THE TEMP OF 1 KG OF THE OBJECT BY 1*C.

Experiment for heat capacity:

- For a block of metal : A block of metal with a heater in and a thermometer (there is gaps in it to fit them). The heater should be connected to a voltmeter and an ammeter. Put insulation, bla bla... Now record the initial temp and final temp, and record the total time THE HEATER WAS ON. Now just apply the rule c=E/(m*(t2-t1)).
C is the specufic heat capacity, m=mass, t2=final temp, t1=initial. Remember that E(energy) can be calculated like this(very imp): E=VxIxT
So We have Voltage and Current (from voltmeter and ammeter on heater) and we know the total time the heater was on. Multiply them to get E. then just apply the rule...


MELTING AND BOILING:


http://www.antonine-education.co.uk/New_items/Gateway/p1_energy_for_the_home_files/image001.gif

So WTF is that... Lemme tell you. As u can see and as u know that when u give smth energy, it becomes hotter, which is exactly what happening in the first line. However the second line shows no change in temp tho we are still giving energy!! WHY? In the first part the energy given was used to make the particles vibrate more... However now that the MELTING POINT is reached, the energy is instead used to loosen the bond between the atoms. Remember, vibrations mean more temp but here its used to loosen the bonds not to add vibrations. Also u have to know that when its used for vibrations it is KINETIC ENERGY, but when its used to loosen the bonds its POTENTIAL ENERGY. Also, the part where the temp is constant shows melting, so there will be BOTH solid and liquid (its still melting). However when it reaches the point where the graph starts to climb again, all the solid is liquid now.
Again the same thing in th beggining happens now, the temp is rising until it reaches boiling point where the energy is instead... bla bla

So, what is this energy called and what is its formula? That my friend willl be in the next episode... (jk xD I will tell u after lunch )

Edit:
The extra energy stored by the water at 0*C, as opposed to ice at 0*C, is the LATENT HEAT OF FUSION
This is they summary of what i explained above!!
The heat required to melt a unit mass of solid, and turned it into liquid is known as the SPECIFIC latent heat of fusion of that solid (symbol L) and is measured in J/Kg or J/g
For gases its called Latent heat of vaporisation

Experiment about Latent Heat:

1-Latent Heat of Fusion of Ice:
a-Weight a beaker without the heater.
b-Dry the ice on a cloth and put into beaker
c-switch heater, start stopwatch
d-stir
e-measure the time taken for the ice to melt
f-weight the beaker plus the water

Very important to know that the FORMULA OF LATENT HEAT IS: L=E/m
this is a bit similar to the previous experiment, all u gotta do is calculate E by VxIxt then divide by m (which is mass of beaker and water - mass of beaker)

2-Latent Heat of Vapourisation of Water:
a- water in beaker
b-weight water+beaker
c-switch on heater
d-WHEN THE WATER BOILS, start the stopwatch and let the water boil for a few minutes
e-weight again

last weight-initial =m and u know the rest......


WATER:
A couple of things u need to know is as i said how it expands below 4C, and that water has  a very hight specific heat capacity. This makes it an excelent coolant for machines, bla bla. And this is what makes the temperature of seas and oceans temperature almost steady as they need enormous energy just to increase a couple of degrees.
There is a confusion around the word steam. Steam is colourless and its at 100C. It occurs when u are boiling water in a kettle. THIS IS EXTREMEMLY DANGEROUS. However in a short time it condenses and turn into water droplets which form the whit clouds u see (and u think its steam but its not).

Last thing is bioling is at BIOLING temperature only and molecules from every part of the liquid vapourises (every part means the particles on top and bottom).
Evapouration however happen at any temperature simultaneously and only the particles on the surface vapourise (cuz only these particles have ENOUGH energy to escape)


HOPE THIS HELPS  
Baladya