NEW SCIENCE BLOG!!

Hey there! :)
It's a new school year! (hooray/boo too)
Okay anyways, if you've been following until now, thanks so much! ^^ My new science journal is at http://20304joycechancs.blogspot.sg/.
It's on chemistry this time, cause after the bio and physics modules, the only science left is chemistry!! :D (yay/boo) hahas.

Dear readers

Dear readers,

It's the end of the year already!! (almost) One school year has passed already, which means... no lessons!! yay! :D
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Though I'll miss having lab lessons.. :|

Anyways. Stay tuned, for I'll most probably be setting up another science blog for next year's science module....... CHEMISTRY!!!!... (I think. Cause I've already had bio and Physics.)
I'll post the link up when the next school year starts.

A BIG THANK YOU to all you readers out there!!!! :D

Entry #11

Thermal transfer

There are three types of thermal heat transfer:

-Conduction

-Convection

-Radiation

All these take place in different substances. 

Conduction

Conduction is the process of thermal energy transfer without any flow of the material medium. 

Conductors and Insulators: Conductors and insulators have different mechanisms to transfer of thermal energy. All solids, gases, and liquids are made up of atoms and molecules. Metals contain free electrons  which move randomly between the atoms and molecules, while non-metals don't. Hence, this proves why metals are better conductors of heat. 

From: http://ed.edim.co/6084142/l1_transfer_of_thermal_energy2.pdf?Expires=1348621281&Signature=KYnjENJ2wCnTrHU~8uwJ9whjkpsroWBwXPYKvDobx-YQ0uqNyQlBaNJFXf9dXEnu7pToK0OcRI5fsmjvfsS6evoLVNbUMR6lu0oZdxILHtj4ESY7z9W65af3Y7rGTjw-BZbGUWAEawx6aWn1LfXaFICMQQuCM7YvCE~Ygs5NpCA_&Key-Pair-Id=APKAI3N2VAFIZ34RBHFA

How it works

When thermal energy is supplied to a substance/object, the molecules of the substance/object that is being heated vibrate vigorously. These particles collide with neighboring particles, making them vibrate as well. Kinetic energy of vibrating particles that are being heated is transferred to neighboring particles (can be linked to the Brownian motion of particles bombarding other particles).

When kinetic energy increases, the temperature increases as well. Hence, conducting thermal energy throughout the substance/object. 

Unique to metals

A faster mechanism of thermal energy transfer takes place at the same time by free electron diffusion. The free electrons gain kinetic energy and move faster. The fast-moving electrons then diffuse into cooler pars of the metal. 

in liquids and gases...

The process of conduction is inefficient. Liquid particles are further apart and collisions of particles are less frequent, even lesser in gas. 

Convection

Convection is the process of thermal energy transfer with the flow of the material medium, specifically by means of currents in a fluid (liquids or gases).  

In liquids, convection is the main process of conduction. 

How it works

When fluids are heated, they expand and become less dense, hence, the less dense fluid will rise (from the heating source, obviously). Cooler fluids being more dense will sink to replace the less dense fluids. This movement in fluid due to a difference in its density sets up a convection current. 

Example: Air-conditioners use this property. They are placed near the ceiling, as warmer air rises towards the ceiling, and hence, the air conditioners can cool this air, making the room cooler as the cooler air is less dense and sinks to our level. Same with the heaters you use in winter/cold country (although it is never cold here.. sigh...) 

Convection currents only occur in fluids (duh). Convection involves the bulk movement of fluids which carry the thermal energy around...? 

You can try the ballon and fire experiment... though, it could get messy! :D

Radiation

Radiation is the continual emission of infrared waves from the surface of all bodies, transmitted without the aid of a medium. This is how the heat of the sun gets to Earth. Space is a vacuum, hence, neither convection nor conduction can take place. (Now you get an idea of how hot the sun is!!)

The sun emits electromagnetic waves. A particular type of wave called infrared waves, makes us feel warm. All objects emit this (including YOU). The hotter the object, the greater the radiation.

In general, a good emitter is also a good absorber. Conversely, poor emitters are also poor absorbers. 

Emission occurs when the surrounding of the emitter is cooler than its surroundings, vice versa. Hence, emission and absorption of thermal energy by radiation depends on the surroundings (link to heat flows from a cooler place to a hotter place).

Factors affecting the rate of radiation

-Colour: Black vs White  (shown in the experiment with thermometers)

-Texture: Dull vs shiny

-Surface temperature

-Surface area

Entry #10

More on Heat!!

At freezing point, Length = 16cm

At boiling point, Length = 48

Difference in Length = 32cm

1ºC = 0.32cm

32u à 100 ºC

1ºC = 32÷100u

For 1ºC, no. of cm.

can also be calculated as 1cm, how many ºC.  

Thermometers are calibrated by first, using pure melting ice to determine the zero point (ice point) and then using boiling water to determine the boiling point (100 ºC)

From here, we can divide the scale into 100 equal parts.

Alternatively, we can also use this formula:

Source: http://www.one-school.net/Malaysia/UniversityandCollege/SPM/revisioncard/physics/heat/thermometer.html 

A Question....

Is water a suitable material to be used in a liquid glass thermometer??

No. Water has a very small range of temperature of 0ºC too 100ºC, which is the ice and steam point of water respectively. Also, water is less sensitive to heat, or in other words, water needs a lot of energy to expand than mercury for a change to be noticeable. (That's why in cold countries, only the surface of lakes are frozen, as water gains and loses heat slowly. This can also be attributed to the bottom of the lake maintaining a constant temperature.... that, I'm not too sure either. :p)

Entry #9

Temperature

The temperature is based on the idea of thermal equilibrium to quantify "hotness". 

Process to thermal equilibrium:

When 2 objects of different temperatures are placed in contact with each other, heat will flow from the hotter object to the cooler object unit they have the same temperature. This is NOT necessarily the mid-temperature. When they are in this state, they are in thermal equilibrium.

The temperature of a substance increases when the average velocity of the particles increase. The heat causes an increase of vibrations of particles in the substance.

Temperature Scales

Fahrenheit (ºF)

Celsius/Centigrade (ºC)

Kelvins (K)

All these scales have 2 things in common: A zero point and a scale. 

Celsius/Centigrade: Has 2 fixed points: Melting point of ice (Ice point) and Boiling point of water                        (Steam point)

Fahrenheit: Ice point is 32ºF, Steam point is 212ºF

Kelvin: Same scale as Centigrade scale, change of temperature of 1ºC = change of temperature of 1K. The Kelvin scale only has 1 fixed point, which is the absolute zero, or the point where particles stop moving and cease to have temperature. (0K)

IMPORTANT CONVERSION!!

0K = -237.15ºC

100K = -173.15ºC

Difference = 237.15

ºC = K-273.15

K = ºC-273.15

Thermometers

A thermometer is any device that has a physical property that changes with temperature. 

The range of temperature is the Highest - Lowest temperature reading on the scale. 

Some physical properties

1. Volume of liquid

2. Electrical resistance of metal

3. Pressure of gases in constant vol container

4. Conductivity of a semi-conductor device

Properties of a thermometer

-Sensitivity (How small a change it can register)

-Responsiveness (How fast it registers)

-Range (How wide the range of temperature it can measure)

Okay.... so that's all for now. (Hope everything came out right... my handwriting is nearly unreadable. Xp Was in a rush.)

Entry #8

Heat

Four things that I need to learn for this unit:

1. Kinetic model of matter (Or kinetic theory)

2. Temperature and heat (Thermal energy)

3. Thermometer properties (Reading scales)

4. Thermal energy transfer (The process and rates)

Kinetic Theory

First off, we shall talk about the 3 states of matter. By now, the three states of matter should be very familiar. As I had mentioned in the sound post, the particles of the three states of matter are different, hence, their different qualities. 

Solids

Has fixed shape and volume

Has High density

Normally hard and rigid

Incompressible

The molecules in solids are tightly packed together and have very strong molecular bonds, hence giving them a high density.

Liquids

Has fixed volume

Has no fixed shape

Incompressible

Relatively high density

The molecules of liquids are loosely packed together and can slide over each other, with weaker molecular bonds than solids, hence, they have no fixed shape.

Gas

Has no fixed shape or volume

Compressible

Low density

The molecules of gas have very weak molecular bonds, hence the molecules can move about freely to expand or to be compressed. 

Now, that aside, let's continue to the Brownian motion.

Brownian motion

Particles are constantly moving in random motions. Their movements are unpredictable. Air molecules move around and bombard dust particles, thus we can see dust flying around in front of the projector/bright light because the dust particles are being bombarded by the air molecules. 

Einstein explained that it is not the dust particles (or any other particles) that possess the energy to move, but that it is the air molecules that possess the kinetic energy.

The exact distribution of energy for each particle may not be constant, but the average distribution of energy stays constant.

Before moving on, some processes to take note of...

(I hope you can read my handwriting.... ^^'')

You may ask "What is the difference between evaporation and vaporization?" Now, vaporization takes place at a fixed temperature. Evaporation on the other hand, takes place all the time, any time (any time the substance feels like, anyways. XD..............Just kidding. ) <--- LAME

Okay, back to work.

Particles in constant motion

Molecules are attracted and repelled by mutual forces of attraction and repulsion respectively. When molecules heat up, their kinetic energy increases and when they cool down, their kinetic energy decreases. 

Now, linking back to the three states of matter: 

Solids: Molecules vibrate about fixed positions only. They are held together by very strong intermolecular bonds. Molecules are also closely packed together in a regular pattern, resulting in high density.

Liquids: Molecules are randomly arranged with the particles slightly further apart as compared to solids, resulting in relatively high densities. They are free to move about but are confined within a vessel. 

Gas: The molecules re very far apart. They are randomly arranged and will occupy any available space. This results in low densities. There is very little attraction between molecules and they will move about randomly at very high speeds.

Another Experiment!

This experiment is on the rate of temperature change.

Materials

-Hot water

-1 Silver metallic cups

-1 black metallic cup

-Covers

-Plastic beaker

-2 thermometers

-Laptop!! :)

In the first experiment, we are trying to find out how the color of the container affects the rate of temperature change.

Step 1: Using the plastic beaker, collect 100cm3 of hot water and pour it into the silver metallic cup. Do the same for the black cup.

Step 2: Place the covers on the cups and stick the thermometers into the hot water through the hole in the cover (remember to use a retort stand so that the thermometer is suspended!). 

Step 3: Record the temperature at the start of the experiment, and record the temperature for every minute.

And so the wait begins.....

....Finally!!

Yay. so now, you have the results....

From the data collected, we can see that the color DOES affect the rate of temperature change. The water in the silver cup loses heat faster than the water in the black cup. Hence, we can conclude that black is a better radiator of heat. :D

You can use the laptop to tabulate/make a graph with the data collected so that it is easier to compare.