THERMAL FLASKKKK
Friday, September 5, 2008
Posted by xiaowei aunty at 5:56 AM
APPLICATION OF THERMAL ENERGY TRANSFER
CONDUCTION
Using the conductors and insulators of heat, humans have invented many useful things, that are commonly used in our lifes.
Conductors of heat....
1.cooking utensils
2.soldering iron rods
3.heat exchangers
Insulators of heat.....
1.handles of appliances and untensils
2.table mats
3.sawdust
4.wooden ladles
5.woollen clothes
6.fibreglass, felt and expanded polystyrene foam
CONVECTION
Using convection, many daily electrical appliances are invented.
1.electrical kettles
--the heating coil of the kettle is placed at the bottom of the kettle to aid transfer of thermal energy in water using convection current. As heating of the water takes place, water that are near the heating coils heats up first, causing it to rise and cooler water sinks. And a convection current occurs...
2.Household hot water systems
--the water heated up by the bunsen burner, as hot water rises up, it is sent to tubes then to the sprinklers/taps..
3.air conditioners
--air conditioners are always installed near the ceiling of the a room to facilitate setting up of convection currents. as it gives out cool dry air into the room, and sinks, hot air rises and is drawn into the air conditioner to have it cooled, as air recirculates and the temperature of the air will eventually fall to the desired level.
4.refrigerator
--as the fridge keeps food cold and fresh it needs the help of an air conditioner, therefore its theory of using convection current is also the same as the air conditioners.
RADIATION
many things ae made useful in our daily lifes.
1. teapots
--as shiny surfaces are bad emmiters of radiation, shinny teapots can keep tea warm for a longer period of time as compared to dull coloured containers.
2.greenhouse
--it is useddin cold climate countries to help plants grow better by trapping heat. During the day infrared radiation from the sun is trapped in the greenhouse, warming up the soil and plants in the greenhouse. as contents in the greenhouse gets warm, they start to emit infrared radiation.
3.vacuum flask
--the sophisicated design of the thermal flask is used to keep liquid warm for a long period of time, with the aid of the theory of radiation.
Posted by xiaowei aunty at 5:11 AM
CSI TO THE RESCUEEEEE!!!!
Tuesday, September 2, 2008
I am TOTALLY IN LOVE with CSI!! WHOOOTSS!! HAHAHAAA...oh, and yeh...You know, i wasn't wasting my time chasing just another series, but this show has shown me how science plays a BIG role in solving cases!
In the series, i found devices that crime scene investigators use to spot evidences with the aid of thermal radiation. Well....read up on how they work!!!
Thermal Radiation. Also of value to the forensic scientist is the sensitivity of materials to radiation in the thermal (IR) infrared portion of the electromagnetic spectrum. This heat-seeking ability is responsible for such diverse phenomena as night vision and IR luminescence. Some inks, when exposed to blue-green light, will absorb the radiation and will re-radiate infrared light. This technique utilizes infrared-sensitive film to record the light emanating from the surface of an illegally altered document. IR luminescence has also been used successfully to reveal writing that has been erased. Another important application of infrared photography arises from the differences in IR absorption by different inks. Techniques of IR photography, as well as oblique lighting, have also been used successfully in order to reveal the contents of a document that has been charred in a fire.
Posted by xiaowei aunty at 11:56 PM
CONVECTION AND RADIATION
CONVECTION
Convection is the transfer of thermal energy by means of currents in a fluid(liquid or gas). Convection currents occur only in fluids such as liquids and gases but not in solids, this is because convection involves the bulk movement of the fluids which carry thermal energy with them. For an example, boiling of water. How the water nearer the flame gets heated up and is moved up by the currents to allow cool water to sink and get heated up. And so the cycle goes on...
RADIATION
Radiation is the continual emmision of infarered waves from the surface of all bodies, transmitted without the aid of a medium. Unlike conduction and convection, radiation does not require a medium for energy transfer, which means it can take place in vacuum. For example how thermal energy from the Sun reaches Earth by the process of radiation. The sun emits EM waves , that makes us feel warm are called infrared and thermal energy from the Sun are called radiant heat. In fact, all objects emit some radiant heat, the hotter the object, the greater the amount of radiant heat emitted.
Also, all objects and surfaces obsorbs infrared radiation and the absorbtion will cause the temperature rise! And of course, radiation is emitted by all objects and surfaces, and thus causing the drop in temperature.
Generally, a good emitter of radiant heat, is also a goos absorber of radiant heat, and vice versa.
There are 3 factors that attects the rate of infrared radiation
1. Colour and texture of the surface
-Dull, black surfaces are better absorbers of infrared radiation than shiny, white surfaces.
2. Surface temperature
-The higher the temperature of the surface of the object relative to the surronding temperature, the higher the rate of infrared radiation.
3. Surface area
-Object with the larger surface area will emit infrared radiation at a higher rate.
Posted by xiaowei aunty at 11:18 PM
CONDUCTION
CONDUCTION
Conduction is a process of thermal energy transfer without any flow of the material medium.
For an example, how heat is transferred from the flame of a stove, to the whole pot, while cooking. Thermal energy is transferred without any movement of the material medium.
As different materials conducts heat at different rates, materials which conducts heat at a faster rate are called conductors of heat, whereas materials which conducts heat at a slower rate are called insulators.
How it worked in solids??
As all solids are made up of molecules, when molecules of an are is heated up, it vibrates vigorously and thus collides with the neighbouring molecules, making them vibrate as well. Thus, kinetic energy of the vibrating molecules at the hot are is transferred to the neighbouring particles.
The difference in metals and non-metals are that metals contains many free electrons which move randomly between atoms, while non-metals do not have such free electrons. These free electrons gain kinetic energy and move faster as a result causing the cool areas to heat up faster: free electrons diffusion.
And how it worked in liquids and gases??
Although thermal energy can be conducted from hot regions to cool regions in liquid and gas, however, it is inefficient. Particles in liquids and gas are spaced further apart than those in solids, therefore causing collisions between particles to be less frequent and vigorous. Transfer of Kinetic energy is therefore slowed down, and explains why air is a worse conductor as compared to water, and water being a worse conductor than a solid.
Posted by xiaowei aunty at 10:44 PM
CHAPTER 8--transfer of thermal energy
In this chapter, i learnt how thermal energy is tranferred in solid, liquid and gas.
Also, i got to know that thermal energy ALWAYS flows from a region og higher temperature to a region of lower temperature. And the transfer of energy is only possible when there is a difference in temperature in specific areas. Energy is transferred in 3 processes, CONDUCTION, CONVECTION and RADIATION.
Posted by xiaowei aunty at 9:03 AM
CSI CSI CSI CSI CSI
Oh! while working on this physics blog, i was watching, um.... CSI!! WOW!! ok....and i watched this episode which actually used the Brownian Motion to aid in the solving of a murder case. In this episode, a man called adam was in a conversation with a nurse(a suspect), when adam was doing a pottery piece, when carving the clay. The conversation caused the air molecules around to vibrate, causing the pottery piece to have differing depths and widths, when play back using the device, will be heard as sound, also known as the conversation between the nurse and adam. WELL.....JUST WATCH!!! pay CLOSE ATTENTION at 13:15 to 13:45! when the lady explains how Brownian Motion comes into play and slowly solving the case, by listening to the playback!!
Posted by xiaowei aunty at 8:12 AM
