Light itself doesn’t necessarily have any temperature. For example, the colored lights emitted by the glowing tubes of an advertising sign don’t have any temperature associated with them. They are non-thermal light—that is, light that is not being emitted by a hot object because of its temperature.
To understand the complicated relationship between color and temperature, let’s begin by looking at thermal light. When you ignite a block of black charcoal in the grill, the temperature of that block gradually rises. Throughout the entire process, the block emits light, or more generally, electromagnetic radiation. At first the block is at room temperature and the radiation it emits is invisible infrared light. This light is actually thermal light, meaning that it is emitted by the block because of that block’s temperature and it carries with it thermal energy or heat. You don’t notice this thermal radiation because it’s invisible and dim. It’s indistinguishable from the thermal radiation that the other room-temperature objects around you emit.
But as the block warms up, its thermal radiation brightens and shifts toward shorter wavelengths and higher frequencies. A physicist would say that its “color” is shifting toward the “blue end” of the spectrum. You still can’t see this thermal radiation, but you can begin to feel its thermal energy with your hands or face. You feel warmed by it.
Once the block reaches about 400 or 500o C, you can begin to see a dim red glow. Now the thermal radiation from the block has spread into the far red edge of the visible portion of the spectrum. By 1300o C, the block appears full red and perhaps even a little orange. By 1800o C, it has the yellow glow of a candle and by 2500o C, it is bright yellow-white and burning fast.
Overall, the block emits a range of light that is characteristic of the block’s temperature. The hotter the block is, the shorter the wavelengths of that light—the more toward the “blue end” of the spectrum—and the brighter the light—the more thermal energy it carries. This thermal light doesn’t have a sharply defined wavelength or a simple color. It has a statistical spread of both wavelength and color that is an essential part of the randomness associated with thermal energy. If you were to trap this thermal light in a room full of perfect mirrors, it would be accurate to say that this light has a temperature; it was emitted by an object because of that object’s temperature and it retains all the characteristics associated with that temperature.
Reaction:
It happens if you begin filtering out certain colors from the light, or if you begin adding colors to the light with fluorescent or neon lamps, or light-emitting diodes, or even lasers. In that case you no longer have thermal light. The light’s spectrum of wavelengths and its brightness aren’t characteristic of any particular temperature any more. Thus if you send sunlight through a filter that transmits only red light and ask what temperature that red light has, the answer is that the red light is no longer thermal and has no temperature.
So your question only has meaning if both lights, red and violet, are thermal. A glowing object at about 1300o C will appear red, although it will be a special type of red because of the thermal spread of wavelengths it must contain. And a glowing object at about 15000o C will appear violet, as well as being unbelievably bright. Once again, that violet will not be a pure wavelength, but rather a broad spread of wavelengths that includes a vast amount of ultraviolet light as well as visible. In this special circumstance, you can say that the violet light truly is hotter than the red light.
Tuesday, February 27, 2007
What causes the smoke produced when you extinguish a candle flame?— SB, Plymouth, England
As the candle burns, its wax does more than simply melt. The liquid wax rises up the wick and vaporizes in the tremendous heat of the flame. It is this vaporized, gaseous wax that mixes with air and burns. The wick itself contributes very little to the flame; you are instead looking at burning wax vapor.
When you blow out a candle, the top of the wick remains extremely hot. You can see its incandescent glow for seconds after the flame is gone. It is still hot enough to vaporize wax and also to continue reacting with oxygen in the air via a flameless burning process—the blackened wick is effectively a piece of charcoal. But without an actual flame, most of the vaporized wax doesn’t burn properly. Instead, it condenses in the colder air around the wick to form first a mist of tiny liquid wax droplets and then solid particles.
Reaction:
Usually when lighted, candles usually causes flames but not that huge amount of flames can be produced. But as you turned of the flame, it usually causes flames and it condenses in the colder air and it causes certain droplets and solid particles.
The smoke that you see is primarily these unburned wax particles. They are tiny, translucent spheres that float around in the air like dust particles. They have a strong smell that most of us find irritating, so we like it when the candle’s wick stops burning quickly and cools off so that the wax vaporization process ceases. Check out Lou's Book: How Things Work, The Physics of Everyday Life
When you blow out a candle, the top of the wick remains extremely hot. You can see its incandescent glow for seconds after the flame is gone. It is still hot enough to vaporize wax and also to continue reacting with oxygen in the air via a flameless burning process—the blackened wick is effectively a piece of charcoal. But without an actual flame, most of the vaporized wax doesn’t burn properly. Instead, it condenses in the colder air around the wick to form first a mist of tiny liquid wax droplets and then solid particles.
Reaction:
Usually when lighted, candles usually causes flames but not that huge amount of flames can be produced. But as you turned of the flame, it usually causes flames and it condenses in the colder air and it causes certain droplets and solid particles.
The smoke that you see is primarily these unburned wax particles. They are tiny, translucent spheres that float around in the air like dust particles. They have a strong smell that most of us find irritating, so we like it when the candle’s wick stops burning quickly and cools off so that the wax vaporization process ceases. Check out Lou's Book: How Things Work, The Physics of Everyday Life
Check out Lou's Book: How Things Work, The Physics of Everyday Life
If you fell into a swimming pool full of Jello, would you be able to swim to the other side? — LM, Charlottesville, VA
That question certainly takes me back. Jello was one of the big mysteries of my childhood. At school, I was taught that there are exactly three phases of matter: solid, liquid, and gas. According to my teachers, everything fit neatly into one of those categories. But what about Jello?! To which of these black & white categories did Jello belong? I asked my teachers, and just about everyone else, but no one would tell me. I felt like a subversive, a rebel, and a troublemaker.
What I didn’t know is that rigid categories often oversimplify the world and neglect wonderfully interesting possibilities. 30 years later, I can tell you that Jello actually spans the range from liquid to solid, depending mostly on its concentration. When it’s sufficiently dilute, it’s definitely a thin liquid. When it’s highly concentrated, it’s definitely a stiff, elastic solid. And then there’s the complicated in between.
Reaction:
The basic distinction between a solid and a liquid is how a material responds to stress—how it responds to having its different parts pushed in different directions. If a material flows when stressed and ultimately rearranges itself so as to eliminate the stress, then it’s technically a liquid. If instead it deforms temporarily and then springs back elastically when the stress is removed, then it’s technically a solid.
But the distinction isn’t perfectly sharp; it depends on how patient you are. Some materials respond elastically to stresses of short duration, but flow liquid-like when stressed for long periods of time. Jello is just such a material. When you smack Jello with a spoon, it jiggles elastically; it behaves like a rubbery solid. But if you squeeze Jello for hours in a stack of serving plates in your refrigerator, it gradually deforms; it behaves like a thick liquid. Officially, a material that flows eventually is a liquid and one that never, ever flows is a solid, but who wants to wait that long?
With that long introduction, it’s time to answer your question. Whether or not you can swim across the pool of Jello answer depends on how concentrated the Jello is. If the Jello is sufficiently dilute that it behaves as a liquid, you’ll be able to swim through it. It may take some time, but you’ll eventually get to the other side.
But if the Jello is so concentrated that it behaves as a solid, the best you can do is to dig your way across. The pool might as well be full of dirt.
And between the two extremes of concentration lie a range of possibilities and levels of patience. As the Jello gets more and more concentrated, the time it takes to flow lengthens and the patience you’ll need to swim across the pool increases. Eventually, you’ll need infinite patience, and then it’s time to beginning digging through what is effectively solid Jello.
That question certainly takes me back. Jello was one of the big mysteries of my childhood. At school, I was taught that there are exactly three phases of matter: solid, liquid, and gas. According to my teachers, everything fit neatly into one of those categories. But what about Jello?! To which of these black & white categories did Jello belong? I asked my teachers, and just about everyone else, but no one would tell me. I felt like a subversive, a rebel, and a troublemaker.
What I didn’t know is that rigid categories often oversimplify the world and neglect wonderfully interesting possibilities. 30 years later, I can tell you that Jello actually spans the range from liquid to solid, depending mostly on its concentration. When it’s sufficiently dilute, it’s definitely a thin liquid. When it’s highly concentrated, it’s definitely a stiff, elastic solid. And then there’s the complicated in between.
Reaction:
The basic distinction between a solid and a liquid is how a material responds to stress—how it responds to having its different parts pushed in different directions. If a material flows when stressed and ultimately rearranges itself so as to eliminate the stress, then it’s technically a liquid. If instead it deforms temporarily and then springs back elastically when the stress is removed, then it’s technically a solid.
But the distinction isn’t perfectly sharp; it depends on how patient you are. Some materials respond elastically to stresses of short duration, but flow liquid-like when stressed for long periods of time. Jello is just such a material. When you smack Jello with a spoon, it jiggles elastically; it behaves like a rubbery solid. But if you squeeze Jello for hours in a stack of serving plates in your refrigerator, it gradually deforms; it behaves like a thick liquid. Officially, a material that flows eventually is a liquid and one that never, ever flows is a solid, but who wants to wait that long?
With that long introduction, it’s time to answer your question. Whether or not you can swim across the pool of Jello answer depends on how concentrated the Jello is. If the Jello is sufficiently dilute that it behaves as a liquid, you’ll be able to swim through it. It may take some time, but you’ll eventually get to the other side.
But if the Jello is so concentrated that it behaves as a solid, the best you can do is to dig your way across. The pool might as well be full of dirt.
And between the two extremes of concentration lie a range of possibilities and levels of patience. As the Jello gets more and more concentrated, the time it takes to flow lengthens and the patience you’ll need to swim across the pool increases. Eventually, you’ll need infinite patience, and then it’s time to beginning digging through what is effectively solid Jello.
Saturday, February 10, 2007
Physics Experiments and Inventions
Calculating the heart rate with a pulse plethysmograph
Introduction
Suitable for
Ages 7 - 18
KS2
KS5
When the heart beats, a pressure wave moves out along the arteries at a few metres per second (appreciably faster than the blood actually flows). This pressure wave can be felt at the wrist, but it also causes an increase in the blood volume in the tissues, which can be detected by a plethysmograph. This word comes from the Greek "plethysmos" for increase and is a term for a "fullness" (ie change in volume) measuring device. Over the years, all sorts of Heath-Robinson devices have been used but described here is a photoelectric pulse plethysmograph, which is robust and easy to make and which will allow the beating of the heart to be recorded without the need to make direct electrical connections to the body.
Equipment required
PC with PicoLog datalogging software installed
PC oscilloscope or data logger
Sensor
Amplifier
Experiment setup
Sensor
The sensor consists of a light source and photodetector; light is shone through the tissues and variation in blood volume alters the amount of light falling on the detector. The source and detector can be mounted side by side to look at changes in reflected light or on either side of a finger or earlobe to detect changes in transmitted light. The particular arrangement here uses a wooden clothes peg to hold an infra red light emitting diode and a matched phototransistor . The infra red filter of the phototransistor reduces interference from fluorescent lights, which have a large AC component in their output.
Figure 1: Sensor
The peg is drilled with 3mm holes to take the led, the phototransistor, the pair of wires linking the two and the 2-core screened output cable. The holes for the led and phototransistor are drilled in one go so that they line up. The ends of each side of the peg are filed on the inside to enlarge the gap and pieces of black closed-cell foam (cannibalized from a mouse mat and punched with 3mm holes) are stuck in place (Super Glue / Crazy Glue) to improve grip and make a (more or less) light-tight seal against the skin. At this point, the spring should be adjusted so that the peg will grip an ear lobe while at the same time not being so tight that it excludes blood from a finger. Pieces of strip-board glued to the peg are used to make connections to the wires; two copper strips wide for the led (anode and cathode connections) and three for the phototransistor side (collector, emitter and led cathode, and led anode - led wires coming through the peg from the other side). The light-emitting diode (Siemens SFH487) and the phototransistor (Siemens SFH309FA) are wedged in their holes and soldered to their respective pieces of strip board. Neither component is critical and many other types will work. The wires are then soldered in place; the screen of the connecting lead is soldered to the emitter and cathode copper pad. Once everything has been checked and proved to work, the connections and the backs of the components should be covered with a bead of an opaque silicone rubber caulk which will insulate and keep out extraneous light. All bare wires should be covered.
Figure 2: Constructing the sensor
Amplifier
The amplifier (see figure 3) uses an LM358 dual op amp to provide two identical broadly-tuned band pass stages with gains of 100. Again, the type of op amp is not particularly critical, as long as it will work at 6V and drive the output rail to rail. The signal frequencies are boxed in by movement artefacts at the low end (generated by the peg moving and distorting the underlying tissues; light pegs are better) and at the top end by mains-hum interference. The circuit runs from a single 6 Volt battery and the output zero is offset by about 1 Volt by referring everything to an internal common line at a voltage set by a pair of forward-biased silicon diodes. This is convenient for interfaces with a 0-5Volt input. The potentiometer allows the overall gain to be adjusted so as to prevent clipping on large signals. Components are not critical but the two 2.2 µF capacitors must be able to stand some reverse bias so they should be non-polarized or tantalum. The circuit can easily be made up on a small piece of strip
Figure 3: Pulse plethysmograph amplifier circuit
Carrying out the experiment
Connect the output of the amplifier to the input of the interface and run PicoLog set to record 500 samples at 20ms intervals. Switch on and clip the peg to an earlobe or index finger; wait for about 10 seconds to allow the circuit to settle and then start recording. Adjust the potentiometer so that the output is about 2 Volts peak, the trace should then look like that in figure 4, with each pulse wave clearly visible. This was acquired using an ADC200 but with its capability of 100Ms/s it is overkill for this circuit, which should work with DrDAQ, all of the PC oscilloscopes and all but the slowest voltage-input data loggers.
Reaction and recommendation:
As I have read and research about the experiment of Dr.Gj Compton, it may really help a lot in terms of health practices and can also be used by different hospitals nowadays. Because in this experiment it can easily measure beating of the heart and also the pulse rate, change of blood volume in the tissues. can be easy to be recorded and to know without the need to make direct electrical connections to the body. And it can be used by children that ranges from 7-18 years of age. And it really helps because it can save lives of many people who are using it. And it can also be used by animals, it would also be of interest to those studying the medical physics and electronic instrumenttations.
Two problems are common when using a pulse plethysmograph: movement will cause the trace to swing around wildly, so persuade the subject not to move as much and if the subject is very cold (pale, pinched looking) the circulation at the extremities may be reduced to the point where there is very little signal.
A useful feature of Picolog is that, if the alarm is set to trigger at about 1 Volt, there will be a beep in time with the heart beat. Having proved that everything is working, the device can be used for such investigations as comparing individual resting heart rates, following heart rate changes during and after exercise and looking at the changes in heart rate that occur as the subject breaths in and out. For example, figure 5 shows 100 seconds of deep, slow breathing. Two effects, synchronised with ventilation, are visible: variations in heart rate can be seen as changes in the spacing between the pulse waves and variations in the stroke volume of the heart can be seen as changes in the amplitudes of the pulse waves.
Introduction
Suitable for
Ages 7 - 18
KS2
KS5
When the heart beats, a pressure wave moves out along the arteries at a few metres per second (appreciably faster than the blood actually flows). This pressure wave can be felt at the wrist, but it also causes an increase in the blood volume in the tissues, which can be detected by a plethysmograph. This word comes from the Greek "plethysmos" for increase and is a term for a "fullness" (ie change in volume) measuring device. Over the years, all sorts of Heath-Robinson devices have been used but described here is a photoelectric pulse plethysmograph, which is robust and easy to make and which will allow the beating of the heart to be recorded without the need to make direct electrical connections to the body.
Equipment required
PC with PicoLog datalogging software installed
PC oscilloscope or data logger
Sensor
Amplifier
Experiment setup
Sensor
The sensor consists of a light source and photodetector; light is shone through the tissues and variation in blood volume alters the amount of light falling on the detector. The source and detector can be mounted side by side to look at changes in reflected light or on either side of a finger or earlobe to detect changes in transmitted light. The particular arrangement here uses a wooden clothes peg to hold an infra red light emitting diode and a matched phototransistor . The infra red filter of the phototransistor reduces interference from fluorescent lights, which have a large AC component in their output.
Figure 1: Sensor
The peg is drilled with 3mm holes to take the led, the phototransistor, the pair of wires linking the two and the 2-core screened output cable. The holes for the led and phototransistor are drilled in one go so that they line up. The ends of each side of the peg are filed on the inside to enlarge the gap and pieces of black closed-cell foam (cannibalized from a mouse mat and punched with 3mm holes) are stuck in place (Super Glue / Crazy Glue) to improve grip and make a (more or less) light-tight seal against the skin. At this point, the spring should be adjusted so that the peg will grip an ear lobe while at the same time not being so tight that it excludes blood from a finger. Pieces of strip-board glued to the peg are used to make connections to the wires; two copper strips wide for the led (anode and cathode connections) and three for the phototransistor side (collector, emitter and led cathode, and led anode - led wires coming through the peg from the other side). The light-emitting diode (Siemens SFH487) and the phototransistor (Siemens SFH309FA) are wedged in their holes and soldered to their respective pieces of strip board. Neither component is critical and many other types will work. The wires are then soldered in place; the screen of the connecting lead is soldered to the emitter and cathode copper pad. Once everything has been checked and proved to work, the connections and the backs of the components should be covered with a bead of an opaque silicone rubber caulk which will insulate and keep out extraneous light. All bare wires should be covered.
Figure 2: Constructing the sensor
Amplifier
The amplifier (see figure 3) uses an LM358 dual op amp to provide two identical broadly-tuned band pass stages with gains of 100. Again, the type of op amp is not particularly critical, as long as it will work at 6V and drive the output rail to rail. The signal frequencies are boxed in by movement artefacts at the low end (generated by the peg moving and distorting the underlying tissues; light pegs are better) and at the top end by mains-hum interference. The circuit runs from a single 6 Volt battery and the output zero is offset by about 1 Volt by referring everything to an internal common line at a voltage set by a pair of forward-biased silicon diodes. This is convenient for interfaces with a 0-5Volt input. The potentiometer allows the overall gain to be adjusted so as to prevent clipping on large signals. Components are not critical but the two 2.2 µF capacitors must be able to stand some reverse bias so they should be non-polarized or tantalum. The circuit can easily be made up on a small piece of strip
Figure 3: Pulse plethysmograph amplifier circuit
Carrying out the experiment
Connect the output of the amplifier to the input of the interface and run PicoLog set to record 500 samples at 20ms intervals. Switch on and clip the peg to an earlobe or index finger; wait for about 10 seconds to allow the circuit to settle and then start recording. Adjust the potentiometer so that the output is about 2 Volts peak, the trace should then look like that in figure 4, with each pulse wave clearly visible. This was acquired using an ADC200 but with its capability of 100Ms/s it is overkill for this circuit, which should work with DrDAQ, all of the PC oscilloscopes and all but the slowest voltage-input data loggers.
Reaction and recommendation:
As I have read and research about the experiment of Dr.Gj Compton, it may really help a lot in terms of health practices and can also be used by different hospitals nowadays. Because in this experiment it can easily measure beating of the heart and also the pulse rate, change of blood volume in the tissues. can be easy to be recorded and to know without the need to make direct electrical connections to the body. And it can be used by children that ranges from 7-18 years of age. And it really helps because it can save lives of many people who are using it. And it can also be used by animals, it would also be of interest to those studying the medical physics and electronic instrumenttations.
Two problems are common when using a pulse plethysmograph: movement will cause the trace to swing around wildly, so persuade the subject not to move as much and if the subject is very cold (pale, pinched looking) the circulation at the extremities may be reduced to the point where there is very little signal.
A useful feature of Picolog is that, if the alarm is set to trigger at about 1 Volt, there will be a beep in time with the heart beat. Having proved that everything is working, the device can be used for such investigations as comparing individual resting heart rates, following heart rate changes during and after exercise and looking at the changes in heart rate that occur as the subject breaths in and out. For example, figure 5 shows 100 seconds of deep, slow breathing. Two effects, synchronised with ventilation, are visible: variations in heart rate can be seen as changes in the spacing between the pulse waves and variations in the stroke volume of the heart can be seen as changes in the amplitudes of the pulse waves.
Saturday, February 3, 2007
physics ultrasound
Ultrasound
Ultrasound is sound with a frequency greater than the upper limit of human hearing, this limit being approximately 20 kilohertz (20,000 hertz).
Approximate frequency ranges corresponding to ultrasound, with rough guide of some applications
A fetus in its mother's womb, viewed in a sonogram (brightness scan)
Ability to hear ultrasound
Some animals, such as dogs, dolphins, bats, and mice have an upper frequency limit that is greater than that of the human ear and thus can hear ultrasound. Children can hear some high-pitched sounds that older adults cannot hear, as in humans the upper limit pitch of hearing gets lower with age (a cell phone company has used this to create ring signals only able to be heard by younger humans[1]). This frequency limit is caused by the middle ear that acts as a low-pass filter. If ultrasound is fed directly into the skull bone and reaches the cochlea without passing through the middle ear, much higher frequencies (up to about 200 kHz) can be heard. This effect (sometimes called ultrasonic hearing) was first discovered by divers exposed to a high-frequency (ca. 50 kHz) sonar signal.
Sonogram of a fetus at 14 weeks (Profile)
Diagnostic sonography
A fetus, aged 29 weeks, in a "3D ultrasound"
Main article: Medical Sonography
Medical sonography (ultrasonography) is a useful ultrasound-based diagnostic medical imaging technique used to visualize muscles, tendons, and many internal organs, their size, structure and any pathological lesions. They are also used to visualize a fetus during routine and emergency prenatal care. Ultrasound scans are performed by medical health care professionals called sonographers. Obstetric sonography is commonly used during pregnancy.
Ultrasound is generally regarded as a "safe test" because it does not use ionising radiation as in x-rays, nuclear medicine, or CT. But it is a form of energy, and scans should only be performed for a suitable medical indication by trained operators (sonographers). Scans performed for baby photos are considered by the profession to be unethical.
The biggest danger of ultrasound is often considered to be misdiagnosis by untrained operators.
A study on rodent fetus brains that are exposed to ultrasound showed signs of damage. Speculation on human fetuses can be in a range of no significant complications to variety of mental and brain disorder. The study shows that rodent brain cells failed to grow to their proper position and remained scattered in incorrect parts of the brain. The conditions of this experiment are different from typical fetal scanning because of the long dwell times. Care should be taken to use low power settings and avoid pulsed wave scanning of the fetal brain unless specifically indicated in high risk pregnancies.
Diagnostic Sonography is dangerous if not treated with the absolute competence.
Ultrasound and animals
Bats
Bats use a variety of ultrasonic ranging (echolocation) techniques to detect their prey.
Dogs
The dog whistle is used to call to a dog. It makes ultrasound at a frequency in the range of 16000 Hz to 22000 Hz that dogs can hear.
Dolphins and whales
It is well known that dolphins and some whales can hear ultrasound and have their own natural sonar system.
Fish
Several types of fish can detect ultrasound. Of the order Clupeiformes, members of the subfamily Alosinae (shad), have been shown to be able to detect sounds up to 180 kHz, while the other subfamilies (e.g. herrings) can hear only up to 4 kHz.[6]
Moths
There is evidence that ultrasound in the range emitted by bats causes flying moths to make evasive manoeuvres, because bats eat moths. Ultrasonic frequencies trigger a reflex action in the noctuid moth that cause it to drop a few inches in its flight to evade attack. [3]
Rodents/Insects
Ultrasound generator/speaker systems are sold with claims that they frighten away rodents and insects, but there is no scientific evidence that the devices work. Controlled tests on some of the systems have shown that rodents quickly learn that the speakers are harmless. The frequency used however is often within the range that most children can hear, and can cause headaches.
Mosquitoes
There is a theory that ultrasound of certain frequencies, while not audible to humans, repel mosquitoes. There are computer programs available on the internet that claim to use this phenomenon for pest-control. There have been mixed reports about the effectiveness of this method towards mosquito-control.
Reaction:
Ultrasound also has therapeutic applications, which can be highly beneficial when used with dosage precautions. Ultrasounds usually uses a special kind of radiation that really helps a lot in examining and treating any conditions that a human can experience. Radiation in physic has many uses like in some machineries that are being used in some institutions.
According to Radiology Ultrasounds are useful in the detection of Pelvic abnormalities and can involve techniques known as abdominal (transabdominal) ultrasound, vaginal (transvaginal or endovaginal) ultrasound in women, and also rectal (transrectal) ultrasound in men.
Treating benign and malignant tumors and other disorders, via a process known as Focused Ultrasound Surgery (FUS) or HIFU, High Intensity Focused Ultrasound. These procedures generally use lower frequencies than medical diagnostic ultrasound (from 250 kHz to 2000 kHz), but significantly higher time-averaged intensities. The treatment is often guided by MRI, as in Magnetic Resonance guided Focused Ultrasound.
More powerful ultrasound sources may be used to clean teeth in dental hygiene or generate local heating in biological tissue, e.g. in occupational therapy, physical therapy and cancer treatment.
Extracorporeal shock wave lithotripsy uses a powerful focused ultrasound source to break up kidney stones.Focused ultrasound sources may be used for cataract treatment by phacoemulsification. Additional physiological effects of low-intensity ultrasound have recently been discovered, e.g. the ability to stimulate bone-growth and its potential to disrupt the blood-brain barrier for drug delivery.
Ultrasound is used in UAL (= ultrasound-assisted lipectomy), or liposuction.
Doppler ultrasound is being tested for use in aiding tissue plasminogen activator treatment in stroke sufferers. This procedure is called Ultrasound-Enhanced Systemic Thrombolysis.
Ultrasound is sound with a frequency greater than the upper limit of human hearing, this limit being approximately 20 kilohertz (20,000 hertz).
Approximate frequency ranges corresponding to ultrasound, with rough guide of some applications
A fetus in its mother's womb, viewed in a sonogram (brightness scan)
Ability to hear ultrasound
Some animals, such as dogs, dolphins, bats, and mice have an upper frequency limit that is greater than that of the human ear and thus can hear ultrasound. Children can hear some high-pitched sounds that older adults cannot hear, as in humans the upper limit pitch of hearing gets lower with age (a cell phone company has used this to create ring signals only able to be heard by younger humans[1]). This frequency limit is caused by the middle ear that acts as a low-pass filter. If ultrasound is fed directly into the skull bone and reaches the cochlea without passing through the middle ear, much higher frequencies (up to about 200 kHz) can be heard. This effect (sometimes called ultrasonic hearing) was first discovered by divers exposed to a high-frequency (ca. 50 kHz) sonar signal.
Sonogram of a fetus at 14 weeks (Profile)
Diagnostic sonography
A fetus, aged 29 weeks, in a "3D ultrasound"
Main article: Medical Sonography
Medical sonography (ultrasonography) is a useful ultrasound-based diagnostic medical imaging technique used to visualize muscles, tendons, and many internal organs, their size, structure and any pathological lesions. They are also used to visualize a fetus during routine and emergency prenatal care. Ultrasound scans are performed by medical health care professionals called sonographers. Obstetric sonography is commonly used during pregnancy.
Ultrasound is generally regarded as a "safe test" because it does not use ionising radiation as in x-rays, nuclear medicine, or CT. But it is a form of energy, and scans should only be performed for a suitable medical indication by trained operators (sonographers). Scans performed for baby photos are considered by the profession to be unethical.
The biggest danger of ultrasound is often considered to be misdiagnosis by untrained operators.
A study on rodent fetus brains that are exposed to ultrasound showed signs of damage. Speculation on human fetuses can be in a range of no significant complications to variety of mental and brain disorder. The study shows that rodent brain cells failed to grow to their proper position and remained scattered in incorrect parts of the brain. The conditions of this experiment are different from typical fetal scanning because of the long dwell times. Care should be taken to use low power settings and avoid pulsed wave scanning of the fetal brain unless specifically indicated in high risk pregnancies.
Diagnostic Sonography is dangerous if not treated with the absolute competence.
Ultrasound and animals
Bats
Bats use a variety of ultrasonic ranging (echolocation) techniques to detect their prey.
Dogs
The dog whistle is used to call to a dog. It makes ultrasound at a frequency in the range of 16000 Hz to 22000 Hz that dogs can hear.
Dolphins and whales
It is well known that dolphins and some whales can hear ultrasound and have their own natural sonar system.
Fish
Several types of fish can detect ultrasound. Of the order Clupeiformes, members of the subfamily Alosinae (shad), have been shown to be able to detect sounds up to 180 kHz, while the other subfamilies (e.g. herrings) can hear only up to 4 kHz.[6]
Moths
There is evidence that ultrasound in the range emitted by bats causes flying moths to make evasive manoeuvres, because bats eat moths. Ultrasonic frequencies trigger a reflex action in the noctuid moth that cause it to drop a few inches in its flight to evade attack. [3]
Rodents/Insects
Ultrasound generator/speaker systems are sold with claims that they frighten away rodents and insects, but there is no scientific evidence that the devices work. Controlled tests on some of the systems have shown that rodents quickly learn that the speakers are harmless. The frequency used however is often within the range that most children can hear, and can cause headaches.
Mosquitoes
There is a theory that ultrasound of certain frequencies, while not audible to humans, repel mosquitoes. There are computer programs available on the internet that claim to use this phenomenon for pest-control. There have been mixed reports about the effectiveness of this method towards mosquito-control.
Reaction:
Ultrasound also has therapeutic applications, which can be highly beneficial when used with dosage precautions. Ultrasounds usually uses a special kind of radiation that really helps a lot in examining and treating any conditions that a human can experience. Radiation in physic has many uses like in some machineries that are being used in some institutions.
According to Radiology Ultrasounds are useful in the detection of Pelvic abnormalities and can involve techniques known as abdominal (transabdominal) ultrasound, vaginal (transvaginal or endovaginal) ultrasound in women, and also rectal (transrectal) ultrasound in men.
Treating benign and malignant tumors and other disorders, via a process known as Focused Ultrasound Surgery (FUS) or HIFU, High Intensity Focused Ultrasound. These procedures generally use lower frequencies than medical diagnostic ultrasound (from 250 kHz to 2000 kHz), but significantly higher time-averaged intensities. The treatment is often guided by MRI, as in Magnetic Resonance guided Focused Ultrasound.
More powerful ultrasound sources may be used to clean teeth in dental hygiene or generate local heating in biological tissue, e.g. in occupational therapy, physical therapy and cancer treatment.
Extracorporeal shock wave lithotripsy uses a powerful focused ultrasound source to break up kidney stones.Focused ultrasound sources may be used for cataract treatment by phacoemulsification. Additional physiological effects of low-intensity ultrasound have recently been discovered, e.g. the ability to stimulate bone-growth and its potential to disrupt the blood-brain barrier for drug delivery.
Ultrasound is used in UAL (= ultrasound-assisted lipectomy), or liposuction.
Doppler ultrasound is being tested for use in aiding tissue plasminogen activator treatment in stroke sufferers. This procedure is called Ultrasound-Enhanced Systemic Thrombolysis.
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