Why does a flame burn upwards?

Why does a flame burn upwards?

We are familiar with how flames burn. Let it be a tear shaped candle flame or a forest fire, it always burns upwards. We will look into the details later, but the following image released by NASA says it all - 

An illustration of how candle burns on earth and in zero gravity

Courtesy: http://science.nasa.gov/

Gravity does the magic: 

Its obvious from the above illustration that gravity has a role to play. However, one can't help but wonder why a flame would go upwards where there is strong gravitation pull like on earth and remain spherical where there is no gravity like on a space station (Is there really no gravitational pull in space?). The answer is buoyancy.

When you start a fire, fuel combines with oxygen to release heat, light, carbon dioxide, water vapor, soot etc. The heat energy generated in this process heats up the air around the flame which in turn reduces its density** (a good analogy is water vapor which is hotter and less denser as against water which is colder and heavier).

This hot air around the flame then starts rising up and the surrounding colder heavier air rushes down into its place accelerating the hot air upwards which in turn causes the flame to shoot up (a good analogy here is a wooden log dipped in water. the buoyancy pushes the log to the surface). Basically the buoyancy shoots the flame up. It is this hot air rushing upwards that also causes fire to flicker.

The following image shows what happens to the air around a flame.

Hot air around the flame rises up shoots the flame upwards

However, in a micro gravity environment, there is no reason for the heavier air to fall down and rush into the place of the lighter air. So the flame just remains a spherical blob as you would imagine. 

So there you have it. A combination and gravity and gravity induced buoyancy causes the hot air to rise up causing the flames to point upwards here on earth.

**Just in case you are curious as to why hot air is less denser than cold air in the first place - the heat gives the molecules in the gas higher (kinetic) energy. So these molecules can move faster and further apart because they now have the energy needed to overcome their binding forces. The molecules being farther apart means that the material is less dense.

The jar of life

A message given by a professor in a wonderful way.....he compared life with a empty jar

"if u spent your all energy and time for small stuff, u never get a time to manage important things"...similar like "if u fill the empty jar with sand first, u never get a place to add golf balls are anything more"

the second video can describe clearly

Total Internal Reflection (TIR) using a Soda Bottle

Figure 1: Total Internal Reflection (TIR) causes light to bend through a stream of water.

 

Figure 2: A laser is pointed at a soda pop bottle with a hole at the bottom. Total internal reflection (TIR) is produced in a stream of water due to the water and light barrier.

The Video Explanation

Explanation

When light crosses into a new medium, some of the light will refract (bend) and some of it will reflect. The angle of refraction is given by Snell's Law:

Where n is the index of refrection, a property unique to each material. This, and the reflection, is shown in the following diagram.

Figure 4: Light refracts and reflects at the barrier between air and water.

Where θ1 is the angle of incidence, or the angle of the source of light, θr is the angle of reflection, and θ2 is the angle of refraction. However, Snell's Law will result in error when n1 is greater than n2. This is called a critical angle, and it is the minimum angle at which all light is reflected. The critical angle can be defined by:

This is the limiting case. If n1 ≥ n2, then θ2 = 90°.

Figure 5: At the critical angle, light travels through the plane where the two media meet.
In this case, nair = 1.00 nwater = 1.33. Therefore:

In this demo light will continually reflect through the stream of water creating total internal reflection (TIR). The stream of water will 'carry' the light though, to the end of the stream.

Figure 6: Total Internal Reflection (TIR) causes light to bend through a stream of water.

Total Internal Reflection is the principle behind fiber optics.

Figure 7: Total Internal Reflection is used to carry light in fiber optics.

For more information see Wikipedia's entry on Fiber Optics. http://en.wikipedia.org/wiki/Optical_fiber.

   Materials

• empty soda pop bottle (2 liter)
• tape
• hand drill
• drill bits
• water
• green laser
• bucket
• old books, etc for stands

Procedure

1. First set up the soda bottle by drilling a hole near the bottom of the bottle. Begin with a drill bit that has a diameter which is slightly larger than the diameter of the laser that will be used. We used a 1/4 inch drill bit, however sizes as small as 7/32 inch worked as well. 
2. First tape the hole and then fill the bottle with water. The cap will prevent leaking because it creates a vacuum in the bottle. 
3. Stand the soda bottle on top of a stack of books so the hole is facing the bucket. The laser should be placed in a binder clip so it stays on, and then set on a stack of books and papers. The laser should be lined up so that the laser light goes through the soda bottle, and into the center of the hole. See Figure 2 (top left picture) for details. 
4. Carefully remove the tape and then unscrew the top of the soda bottle. The light should reflect within the stream of water so that you could see at least a few points of reflection. The light should be visible through the entire stream. 
5. If the reflections of the light isn't clear, it may be necessary to expand the hole by drilling through the existing hole with a larger drill bit. This process may need to be repeated several times.

    Notes

• This is an messy experiment. Be ready to adjust the bucket which catches the stream of water. 
• Also be aware that the stream's curvature will change as the water level decreases. It will bend closer to the bottle, and the bucket may need to be adjusted again. When the water level is a little above the hole there will be no total internal reflection although the stream will continue. Place the cap back on, or put the bottle inside of the bucket. 
• Make sure to have lots of paper towels! Towels or rags could be useful too. However, this mess is water, and therefore easy to clean up. 
• Some resources suggest putting a drop of food coloring in the bottom of the bucket to match the laser light, giving the appearance that the water has permanently 'trapped' the colored light. This is a magic trick, and may cause students to misunderstand what total internal reflection is.

  References

http://wildcat.phys.northwestern.edu/vpl/optics/snell.htmlThis site contains an applet which allows the user to change the angles and indices of refraction. It is a more simple and straight version compared to Stony Brook's (the link below).
http://www.eserc.stonybrook.edu/ProjectJava/snell/This site is an applet which allows the user to change the angles and indices of refraction in order to observe reflection and refraction. There is a 'simpler version' option.
http://en.wikipedia.org/wiki/Total_internal_reflection
The Wikipedia entry on Total Internal Reflection
http://hyperphysics.phy-astr.gsu.edu/Hbase/phyopt/totint.html
An explanation of total internal reflection with drawings. It includes a calculator which determines the critical angle when the indices of reflection are provided.
http://www.glenbrook.k12.il.us/gbssci/phys/CLass/refrn/u14l3b.html
This is a tutorial on Total Internal Reflection with many drawings to explain the concepts.

Using the high-low side driver IR2110 - explanation and plenty of example circuits

Using the high-low side driver IR2110 - explanation and plenty of example circuits

In many situations, we need to use MOSFETs configured as high-side switches. Many a times we need to use MOSFETs configured as high-side and low-side switches. Such as in bridge circuits. In half-bridge circuits, we have 1 high-side MOSFET and 1 low-side MOSFET. In full-bridge circuits we have 2 high-side MOSFETs and 2 low-side MOSFETs. In such situations, there is a need to use high-side drive circuitry alongside low-side drive circuitry. The most common way of driving MOSFETs in such cases is to use high-low side MOSFET drivers. Undoubtedly, the most popular such driver chip is the IR2110. And in this article/tutorial, I will talk about the IR2110.

You can download the IR2110 datasheet from the IR website. Here's the download link:

www.irf.com/product-info/datasheets/data/ir2110.pdf

First let’s take a look at the block diagram and the pin assignments and pin definitions (also called lead assignments and lead definitions):

Fig. 1 - IR2110 block diagram (click on image to enlarge)

Fig. 2 - IR2110 Pin/Lead Assignments (click on image to enlarge)

Fig. 3 - IR2110 Pin/Lead Definitions (click on image to enlarge)

Notice that the IR2110 comes in two packages – 14 pin through-hole PDIP package and the 16-pin surface mount SOIC package.

Now let's talk about the different pins.

VCC is the low-side supply and should be between 10V and 20V. VDD is the logic supply to the IR2110. It can be between +3V to +20V (with reference to VSS). The actual voltage you choose to use depends on the voltage level of your input signals. Here’s the chart:

Fig. 4 - IR2110 Logic "1" Input Threshold vs VDD (click on image to enlarge)

It is common practice to use VDD = +5V. When VDD = +5V, the logic 1 input threshold is slightly higher than 3V. Thus when VDD = +5V, the IR2110 can be used to drive loads when input “1” is higher than 3 point something volts. This means that it can be used for almost all circuits, since most circuits tend to have around 5V outputs. When you’re using microcontrollers the output voltage will be higher than 4V (when the microcontroller has VDD = +5V, which is quite common). When you’re using SG3525 or TL494 or other PWM controller, you are probably going to have them powered off greater than 10V, meaning the outputs will be higher than 8V when high. So, the IR2110 can be easily used.

You may lower the VDD down to about 4V if you’re using a microcontroller or any chip that gives output of 3.3V (eg dsPIC33). While designing circuits with the IR2110, I had noticed that sometimes the circuit didn’t work properly when IR2110 VDD was selected as less than +4V. So, I do not recommend using VDD less than +4V.

In most of my circuits, I do not have signal levels which have voltages less than 4V as high and so I use VDD = +5V.

If for some reason, you have signals levels with logic “1” having lower than 3V, you will need a level converter / translator that will boost the voltage to acceptable limits. In such situations, I recommend boosting up to 4V or 5V and using IR2110 VDD = +5V.

Now let’s talk about VSS and COM. VSS is the logic supply ground. COM is “low side return” – basically, low side drive ground connection. It seems that they are independent and you might think you could perhaps isolate the drive outputs and drive signals. However, you’d be wrong. While they are not internally connected, IR2110 is a non-isolated driver, meaning that VSS and COM should both be connected to ground.

HIN and LIN are the logic inputs. A high signal to HIN means that you want to drive the high-side MOSFET, meaning a high output is provided on HO. A low signal to HIN means that you want to turn off the high-side MOSFET, meaning a low output is provided on HO. The output to HO – high or low – is not with respect to ground, but with respect to VS. We will soon see how a bootstrap circuitry (diode + capacitor) – utilizing VCC, VB and VS – is used to provide the floating supply to drive the MOSFET. VS is the high side floating supply return. When high, the level on HO is equal to the level on VB, with respect to VS. When low, the level on HO is equal to VS, with respect to VS, effectively zero.

A high signal to LIN means that you want to drive the low-side MOSFET, meaning a high output is provided on LO. A low signal to LIN means that you want to turn off the low-side MOSFET, meaning a low output is provided on LO. The output on LO is with respect to ground. When high, the level on LO is equal to the level of VCC, with respect to VSS, effectively ground. When low, the level on LO is equal to the level on VSS, with respect to VSS, effectively zero.

SD is used as shutdown control. When this pin is low, IR2110 is enabled – shutdown function is disabled. When this pin is high, the outputs are turned off, disabling the IR2110 drive.

Now let’s take a look at the common IR2110 configuration for driving MOSFETs in both high and low side configurations – a half bridge stage.

Fig. 5 - Basic IR2110 circuit for driving half-bridge (click on image to enlarge)

D1, C1 and C2 along with the IR2110 form the bootstrap circuitry. When LIN = 1 and Q2 is on, C1 and C2 get charged to the level on VB, which is one diode drop below +VCC. When LIN = 0 and HIN = 1, this charge on the C1 and C2 is used to add the extra voltage – VB in this case – above the source level of Q1 to drive the Q1 in high-side configuration. A large enough capacitance must be chosen for C1 so that it can supply the charge required to keep Q1 on for all the time. C1 must also not be too large that charging is too slow and the voltage level does not rise sufficiently to keep the MOSFET on. The higher the on time, the higher the required capacitance. Thus, the lower the frequency, the higher the required capacitance for C1. The higher the duty cycle, the higher the required capacitance for C1. Yes, there are formulae available for calculating the capacitance. However, there are many parameters involved, some of which we may not know – for example, the capacitor leakage current. So, I just estimate the required capacitance. For low frequencies such as 50Hz, I use between 47µF and 68µF capacitance. For high frequencies like 30kHz to 50kHz, I use between 4.7µF and 22µF. Since we’re using an electrolytic capacitor, a ceramic capacitor should be used in parallel with this capacitor. The ceramic capacitor is not required if the bootstrap capacitor is tantalum.

D2 and D3 discharge the gate capacitances of the MOSFET quickly, bypassing the gate resistors, reducing the turn off time. R1 and R2 are the gate current-limiting resistors.

+MOSV can be up to a maximum of 500V.

+VCC should be from a clean supply. You should use filter capacitors and decoupling capacitors from +VCC to ground for filtering.

Now let’s look at a few example application circuits of the IR2110.

Fig. 6 - IR2110 circuit for high-voltage half-bridge drive (click on image to enlarge)

Fig. 7 - IR2110 circuit for high-voltage full-bridge drive with independent switch control (click on image to enlarge)

In Fig. 7 we see the IR2110 being used to drive a full bridge. The functionality is simple and you should understand it by now. A common thing that is often done is that, HIN1 is tied/shorted to LIN2 and HIN2 is tied/shorted to LIN1, enabling the control of all 4 MOSFETs from 2 signal inputs, instead of 4 as shown below in Fig. 8.

Fig. 8 - IR2110 circuit for high-voltage full-bridge drive with tied switch control - control with 2 input signals (click on image to enlarge)

Fig. 9 - Using the IR2110 as a single high-voltage high-side driver (click on image to enlarge)

In Fig. 9 we see the IR2110 being used as a single high-side driver. The circuit is simple enough and follows the same functionality described above. One thing to remember is that, since there is no low-side switch, there must a load connected from OUT to ground. Otherwise the bootstrap capacitors can not charge.

Fig. 10 - Using the IR2110 as a single low-side driver (click on image to enlarge)

Fig. 11 - Using the IR2110 as a dual low-side driver (click on image to enlarge)

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If you've had failures with IR2110 and had driver after driver, MOSFET after MOSFET get damaged, burn and fail, I'm pretty sure that it's due to you not using gate-to-source resistors, assuming of course that you designed the IR2110 driver stage properly. NEVER OMIT THE GATE-TO-SOURCE RESISTORS. If you're curious, you can read about my experience with them here (I have also explained the reason that the resistors prevent damage):

http://tahmidmc.blogspot.com/2012/10/magic-of-knowledge.html

Most order-able thing in world

Physics gives wonders, if u know all properties means. we can argue in our own way to make convenient answers.
Are u ....confused.....read the conversation given below...

Teacher asked to a student, give me 4 examples for liquids
student: Baby rabbits, Baby Cats, Baby rats, Water,....etc
Teacher: What???.....water is liquid, ok....how rabbits,cats,rats...are becomes liquids???
student: "Liquids takes the shape of the container while maintain the constant volume". That"s It. Baby rabbits,cats,rats doing same...."So Baby rabbits,cats,rats are liquids."

...that"s why i like physics.:)
..............................................by Reddyprasad.R

See the video......if u have doubts means