The figure above [ link] shows how light is separated into different colors with a prism—a piece of glass in the shape of a triangle with refracting surfaces.
Upon entering one face of the prism, the path of the light is refracted bent , but not all of the colors are bent by the same amount. The bending of the beam depends on the wavelength of the light as well as the properties of the material, and as a result, different wavelengths or colors of light are bent by different amounts and therefore follow slightly different paths through the prism.
The violet light is bent more than the red. Upon leaving the opposite face of the prism, the light is bent again and further dispersed. If the light leaving the prism is focused on a screen, the different wavelengths or colors that make up white light are lined up side by side just like a rainbow [link]. In fact, a rainbow is formed by the dispersion of light though raindrops; see The Rainbow feature box. Because this array of colors is a spectrum of light, the instrument used to disperse the light and form the spectrum is called a spectrometer.
Continuous Spectrum. When white light passes through a prism, it is dispersed and forms a continuous spectrum of all the colors. Although it is hard to see in this printed version, in a well-dispersed spectrum, many subtle gradations in color are visible as your eye scans from one end violet to the other red. When Newton described the laws of refraction and dispersion in optics, and observed the solar spectrum, all he could see was a continuous band of colors.
With this device, Wollaston saw that the colors were not spread out uniformly, but instead, some ranges of color were missing, appearing as dark bands in the solar spectrum. He mistakenly attributed these lines to natural boundaries between the colors. In , German physicist Joseph Fraunhofer , upon a more careful examination of the solar spectrum, found about such dark lines missing colors , which led scientists to rule out the boundary hypothesis [link].
Visible Spectrum of the Sun. They did this by passing their light through various apparently transparent substances—usually containers with just a bit of thin gas in them. These gases turned out not to be transparent at all colors: they were quite opaque at a few sharply defined wavelengths. Something in each gas had to be absorbing just a few colors of light and no others.
All gases did this, but each different element absorbed a different set of colors and thus showed different dark lines. If the gas in a container consisted of two elements, then light passing through it was missing the colors showing dark lines for both of the elements.
This discovery was one of the most important steps forward in the history of astronomy. What would happen if there were no continuous spectrum for our gases to remove light from? What if, instead, we heated the same thin gases until they were hot enough to glow with their own light? When the gases were heated, a spectrometer revealed no continuous spectrum , but several separate bright lines.
Of course this happens without any user intervention, so as long as Airtel has any spectrum and a license in the circle, users are unlikely to notice the difference. The oldest of these is obviously 2G, while 4G is still evolving. These technologies were developed to take advantage of different bands, and this means that you can't just use a technology on any band at will. Bands might be roads, but only specific types of vehicles can travel on them.
That's why your phone needs a modem that can operate on multiple frequencies, so that it can connect to all the bands, and transmit your voice, messages, and data. Initially, LTE required a higher frequency for the greater data speeds it offered, but technology advances made it possible to use MHz instead. Does the frequency matter? So there are a lot of different frequency bands auctioned across different circles, and these bands power different technologies. But are there any differences between the bands?
Apart from the fact that the communication technology was developed for certain bands, what are the advantages of using - for example, the MHz for 4G over the MHz band? As explained right at the start, the higher the frequency, the more the energy is required for the wave.
This is true for any kind of spectrum, not just the telecom spectrum. So for example, the Wi-Fi network in your house can be either 2. Fewer devices operate on 5GHz, so there is very little interference in your Wi-Fi network at this frequency, but on the other hand, the range for a 2. The light emitted by hydrogen atoms is red because, of its four characteristic lines, the most intense line in its spectrum is in the red portion of the visible spectrum, at nm.
With sodium, however, we observe a yellow color because the most intense lines in its spectrum are in the yellow portion of the spectrum, at about nm. Such emission spectra were observed for many other elements in the late 19th century, which presented a major challenge because classical physics was unable to explain them.
Thus the energy levels of a hydrogen atom had to be quantized ; in other words, only states that had certain values of energy were possible, or allowed. If a hydrogen atom could have any value of energy, then a continuous spectrum would have been observed, similar to blackbody radiation.
In , a Swiss mathematics teacher, Johann Balmer — , showed that the frequencies of the lines observed in the visible region of the spectrum of hydrogen fit a simple equation that can be expressed as follows:. As a result, these lines are known as the Balmer series. A mathematics teacher at a secondary school for girls in Switzerland, Balmer was 60 years old when he wrote the paper on the spectral lines of hydrogen that made him famous.
Unfortunately, scientists had not yet developed any theoretical justification for an equation of this form. In , a Danish physicist, Niels Bohr —; Nobel Prize in Physics, , proposed a theoretical model for the hydrogen atom that explained its emission spectrum. Using classical physics, Niels Bohr showed that the energy of an electron in a particular orbit is given by.
In that level, the electron is unbound from the nucleus and the atom has been separated into a negatively charged the electron and a positively charged the nucleus ion.
In this state the radius of the orbit is also infinite. The atom has been ionized. In his final years, he devoted himself to the peaceful application of atomic physics and to resolving political problems arising from the development of atomic weapons. As n decreases, the energy holding the electron and the nucleus together becomes increasingly negative, the radius of the orbit shrinks and more energy is needed to ionize the atom.
Because a hydrogen atom with its one electron in this orbit has the lowest possible energy, this is the ground state the most stable arrangement of electrons for an element or a compound , the most stable arrangement for a hydrogen atom.
Any arrangement of electrons that is higher in energy than the ground state. Except for the negative sign, this is the same equation that Rydberg obtained experimentally.
Because a sample of hydrogen contains a large number of atoms, the intensity of the various lines in a line spectrum depends on the number of atoms in each excited state. In contemporary applications, electron transitions are used in timekeeping that needs to be exact. Telecommunications systems, such as cell phones, depend on timing signals that are accurate to within a millionth of a second per day, as are the devices that control the US power grid.
Global positioning system GPS signals must be accurate to within a billionth of a second per day, which is equivalent to gaining or losing no more than one second in 1,, years. Quantifying time requires finding an event with an interval that repeats on a regular basis. To achieve the accuracy required for modern purposes, physicists have turned to the atom. Consider the spectrum as shown below.
The top spectrum shows a narrow segment of Sun's spectrum of ultraviolet UV light. This representation has been modeled after the visible spectra. Remember that our eyes can't see ultraviolet light; however, as with the visible spectra shown above, the horizontal axis the x-axis shows the energy or "color" of the observed light. The spectrum covers wavelengths of energy between and angstroms. In that representation, we can see where the emission by the Sun is most active, but again we see little about the intensity of the radiation.
There is no quantitative measure of the light emitted as a function of energy. The graph below the Sun's UV spectrum shows the same information in a more quantitative format. As with the other spectra, the x-axis indicates the energy of the observed light.
However, instead of indicating the observed energies with light bands, the graph shows the intensity of the radiation on the y-axis. While the graph isn't as colorful as those shown in a "photographic" format, this representation tells us much about the UV emission of the Sun. Compare the two representations of the solar UV spectrum.
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