The Energy of Different Kinds of Rays
Sufficiently energetic rays can collide and materialize. Like particles, electromagnetic waves also come in “lumps.” Rays are the track or trajectory of these energy lumps. Unlike atoms, electromagnetic waves in free space can be subdivided without losing their characteristics. Therefore the lumps need a different name. The lumps or quanta of electromagnetic waves are called photons.
The word “photon” comes from the Greek word for light. The same word applies to the quanta of all kinds of electromagnetic waves, whether they are the kind that we can see or not.
We may say that photons are “particles” like electrons or protons or neutrons, but some of their characteristics differ. Electrons, protons, and neutrons are material particles, that is, they have mass whether they are moving or not. As they move faster they become more massive because their kinetic energy adds to their mass. Photons have a mass equivalent to their energy, but they have that mass only because they move at the speed of light. Material particles occupy a certain amount of space and usually force other material particles to seek some other location. Any number of photons can fit together in the same space and they all tend to follow the same trajectory, without forcing other photons out of line. In this aspect rays are like lines. A geometric line has zero width. One can bundle many lines together without increasing the width at all.
Photons move along rays like traffic on a highway.
Highway traffic may be mixed, consisting of lightweight economy cars, sports cars, touring cars, heavy luxury cars, buses, light and heavy trucks, and tractor-trailer rigs with 18 wheels or more. These vehicles have a range of sizes and differ in the amounts of cargo they can carry.
Photons differ according to the energy they carry. From less energetic to more energetic these are the photons of radio waves, microwaves, millimeter waves, heat, light, ultraviolet rays, soft X-rays, and hard X-rays or gamma rays.
Traffic on a highway can be slack or intense depending on the time of day or night and on the type of day, whether it is a workday, weekend, or holiday. The intensity of traffic is distinct from the type of traffic. Parkways exclude trucks and buses, but the traffic still ranges in intensity. Similarly, rays may be weak even if their photons have high energy, or intense even if their photons have low energy.
A ray is a track of photons, and photons are packets of waves. Waves vibrate. Vibration means that something is going back and forth or around and around. A cycle is one complete back-and-forth movement or one complete circuit. The vibration rate is also called the frequency, the number of times per second that the movement goes through cycles. Physicists give rates of vibration in a unit named after Heinrich Rudolf Hertz (German physicist, 1857–1894). A cycle per second is called a hertz.
The energy of a photon is proportional to its vibration rate. To get a ray’s energy in watt-seconds or joules, multiply the vibration rate in hertz times Planck’s constant, 662.606 876 micro-micro-micro-micro-micro-microjoule-seconds.
Planck’s constant is a very small number. The vibration rate for electromagnetic waves is usually a large number of cycles per second, but Planck’s constant is so small that the product of the vibration rate and Planck’s constant is almost always a small number. This means that it takes many photons to make up an intense ray, even if the photons are very energetic.
Let’s compare vibration rates using units of one megahertz (MHz), which means one million vibrations per second. Radio waves vibrate relatively slowly. The range for AM radio is from 0.522 MHz to 1.620 MHz. The standard FM radio tunes between 88 MHz and 108 MHz. The waves in a microwave oven vibrate at 2 450 MHz. The only waves we can see are light waves. Their rate of vibration lies between 430 million and 750 million MHz. Gamma rays vibrate more rapidly than any other electromagnetic waves.
We often describe a wave by its length rather than its vibration rate.
The length is the distance between any identifiable feature of a wave and the next repetition of that feature. For instance, the wavelength is the distance from one crest or peak to the next crest or peak. One obtains the same wavelength measuring from one trough or valley to the next trough or valley. Things are a little more complicated if one measures from the midpoint between a crest and trough. The wavelength is the distance from one midpoint to the next on rising slopes, or from one midpoint to the next on falling slopes.
Wavelength and vibration rate are inversely related. The product of wavelength and vibration rate is the speed of the wave. Electromagnetic waves travel in free space at a speed we know as the speed of light. Wavelength is the speed divided by the vibration rate, and the vibration rate is the speed divided by the wavelength. Low-frequency radio waves have long wavelengths and the high-frequency waves of gamma rays have short wavelengths. Photons have wavelengths ranging from long to short as the photon energy increases.
The word “photon” comes from the Greek word for light. The same word applies to the quanta of all kinds of electromagnetic waves, whether they are the kind that we can see or not.
We may say that photons are “particles” like electrons or protons or neutrons, but some of their characteristics differ. Electrons, protons, and neutrons are material particles, that is, they have mass whether they are moving or not. As they move faster they become more massive because their kinetic energy adds to their mass. Photons have a mass equivalent to their energy, but they have that mass only because they move at the speed of light. Material particles occupy a certain amount of space and usually force other material particles to seek some other location. Any number of photons can fit together in the same space and they all tend to follow the same trajectory, without forcing other photons out of line. In this aspect rays are like lines. A geometric line has zero width. One can bundle many lines together without increasing the width at all.
Photons move along rays like traffic on a highway.
Highway traffic may be mixed, consisting of lightweight economy cars, sports cars, touring cars, heavy luxury cars, buses, light and heavy trucks, and tractor-trailer rigs with 18 wheels or more. These vehicles have a range of sizes and differ in the amounts of cargo they can carry.
Photons differ according to the energy they carry. From less energetic to more energetic these are the photons of radio waves, microwaves, millimeter waves, heat, light, ultraviolet rays, soft X-rays, and hard X-rays or gamma rays.
Traffic on a highway can be slack or intense depending on the time of day or night and on the type of day, whether it is a workday, weekend, or holiday. The intensity of traffic is distinct from the type of traffic. Parkways exclude trucks and buses, but the traffic still ranges in intensity. Similarly, rays may be weak even if their photons have high energy, or intense even if their photons have low energy.
A ray is a track of photons, and photons are packets of waves. Waves vibrate. Vibration means that something is going back and forth or around and around. A cycle is one complete back-and-forth movement or one complete circuit. The vibration rate is also called the frequency, the number of times per second that the movement goes through cycles. Physicists give rates of vibration in a unit named after Heinrich Rudolf Hertz (German physicist, 1857–1894). A cycle per second is called a hertz.
The energy of a photon is proportional to its vibration rate. To get a ray’s energy in watt-seconds or joules, multiply the vibration rate in hertz times Planck’s constant, 662.606 876 micro-micro-micro-micro-micro-microjoule-seconds.
Planck’s constant is a very small number. The vibration rate for electromagnetic waves is usually a large number of cycles per second, but Planck’s constant is so small that the product of the vibration rate and Planck’s constant is almost always a small number. This means that it takes many photons to make up an intense ray, even if the photons are very energetic.
Let’s compare vibration rates using units of one megahertz (MHz), which means one million vibrations per second. Radio waves vibrate relatively slowly. The range for AM radio is from 0.522 MHz to 1.620 MHz. The standard FM radio tunes between 88 MHz and 108 MHz. The waves in a microwave oven vibrate at 2 450 MHz. The only waves we can see are light waves. Their rate of vibration lies between 430 million and 750 million MHz. Gamma rays vibrate more rapidly than any other electromagnetic waves.
We often describe a wave by its length rather than its vibration rate.
The length is the distance between any identifiable feature of a wave and the next repetition of that feature. For instance, the wavelength is the distance from one crest or peak to the next crest or peak. One obtains the same wavelength measuring from one trough or valley to the next trough or valley. Things are a little more complicated if one measures from the midpoint between a crest and trough. The wavelength is the distance from one midpoint to the next on rising slopes, or from one midpoint to the next on falling slopes.
Wavelength and vibration rate are inversely related. The product of wavelength and vibration rate is the speed of the wave. Electromagnetic waves travel in free space at a speed we know as the speed of light. Wavelength is the speed divided by the vibration rate, and the vibration rate is the speed divided by the wavelength. Low-frequency radio waves have long wavelengths and the high-frequency waves of gamma rays have short wavelengths. Photons have wavelengths ranging from long to short as the photon energy increases.