All light has both particle-like and wave-like properties. How an instrument is designed to sense the light influences which of these properties are observed. An instrument that diffracts light into a spectrum for analysis is an example of observing the wave-like property of light. The particle-like nature of light is observed by detectors used in digital cameras—individual photons liberate electrons that are used for the detection and storage of the image data.
One of the physical properties of light is that it can be polarized. Polarization is a measurement of the electromagnetic field's alignment. In the figure above, the electric field in red is vertically polarized. Think of a throwing a Frisbee at a picket fence. In one orientation it will pass through, in another it will be rejected.
This is similar to how sunglasses are able to eliminate glare by absorbing the polarized portion of the light. The terms light, electromagnetic waves, and radiation all refer to the same physical phenomenon: electromagnetic energy.
This energy can be described by frequency, wavelength, or energy. All three are related mathematically such that if you know one, you can calculate the other two. Radio and microwaves are usually described in terms of frequency Hertz , infrared and visible light in terms of wavelength meters , and x-rays and gamma rays in terms of energy electron volts.
This is a scientific convention that allows the convenient use of units that have numbers that are neither too large nor too small. The number of crests that pass a given point within one second is described as the frequency of the wave.
One wave—or cycle—per second is called a Hertz Hz , after Heinrich Hertz who established the existence of radio waves. A wave with two cycles that pass a point in one second has a frequency of 2 Hz. Electromagnetic waves have crests and troughs similar to those of ocean waves. The distance between crests is the wavelength.
The shortest wavelengths are just fractions of the size of an atom, while the longest wavelengths scientists currently study can be larger than the diameter of our planet! An electromagnetic wave can also be described in terms of its energy—in units of measure called electron volts eV. An electron volt is the amount of kinetic energy needed to move an electron through one volt potential.
Moving along the spectrum from long to short wavelengths, energy increases as the wavelength shortens. Consider a jump rope with its ends being pulled up and down. More energy is needed to make the rope have more waves. Top of Page Next: Wave Behaviors. Laser beams are light beams but they are different to the light beams that come from torches or the headlights of cars. The most obvious difference is that laser beams do not spread out very much as they travel.
They continue in a beam that hardly gets bigger as it travels, whereas the beam from a torch spreads out as it travels from the torch. Also, laser beams consist of one pure colour only, whereas the white light from a torch globe is a mixture of most of the colours of the spectrum. The other major difference is that the electromagnetic waves in the laser beam all vibrate in step, whereas the waves in the light from a torch light are random and out of step.
The laser beam is said to be coherent light. What this means may be illustrated by comparing it to sound waves. White light is like the noise made by hitting all the keys of a piano at once. Laser light, however, is like a pure note made by a flute, which could be called coherent sound.
Because light travels in straight lines at a fixed speed, lasers are used by architects and builders to measure distances and to get buildings level and in the correct positions. Looking directly into a laser beam can be very dangerous becase it can burn the retina.
Eye surgeons can use a laser beam instead of a scalpel when performing operations. Very high-powered lasers are used in industry to cut sheets of metal or sheets of plastic to exact shapes and sizes or, in tailoring, to cut many layers of cloth at once. Lasers are also used in CD players to scan the surface of the CD to produce music, and in shopping centres to scan the barcodes of things being purchased.
Cable television is a method of receiving television broadcasts through an underground cable, rather then receiving the broadcast using an antenna on the roof of the house. Cables with copper wires can provide a telephone service, but copper wires cannot cope with the huge amount of information that is required for a television picture.
The underground cables transmitting a television signal use optical fibres. Optical fibres are extremely thin fibres of pure, very clear, silica glass. If a ray of light is shone into one end of an optical fibre, it will travel down the fibre for a long distance. This vibration creates a wave which has both an electric and a magnetic component. An electromagnetic wave transports its energy through a vacuum at a speed of 3.
The propagation of an electromagnetic wave through a material medium occurs at a net speed which is less than 3.
This is depicted in the animation below. The mechanism of energy transport through a medium involves the absorption and reemission of the wave energy by the atoms of the material. When an electromagnetic wave impinges upon the atoms of a material, the energy of that wave is absorbed. The absorption of energy causes the electrons within the atoms to undergo vibrations. After a short period of vibrational motion, the vibrating electrons create a new electromagnetic wave with the same frequency as the first electromagnetic wave.
0コメント