Notes

Electromagnetic Radiation:

In the quantum model of the atom, an electron in a higher electron level (further from the nucleus) has more energy than one in a lower level (closer to the nucleus). The quantum model specifically states that electrons can jump from one energy level to another — from high to low or low to high. When an electron drops from a high energy level to a lower one, it emits a packet of light energy, called a photon. The photon given off from an electron when it moves from a higher to lower energy level will differ depending on which energy level it has moved from.

An interesting application of this phenomenon is the laser, where the energy supplied to the atoms excites the electrons into higher orbits. Photons are emitted when the electrons give off the extra energy and return to their usual lower orbits. Fluorescent lights and neon signs use the same principle to emit light.

Light from these energy level transitions exists as electromagnetic radiation, which behaves like a wave.
Let's go over some of the basic concepts related to waves. Look at the two waveforms shown here. Both of them start at the rest line from point O, reach the highest point P, pass through the rest line again, reach the lowest point, and then come back to rest again. This makes one complete cycle, which a wave repeats over and over.

The highest point of a wave is called the crest. The points P and R represent the two crests in consecutive wave cycles. The height of P from the rest line of a wave is called its amplitude. Notice the different amplitudes of the two waves.

The distance between two consecutive crests, such as P and R, is called the wavelength of the wave. Note that the wavelength of the first wave (about 2.5 units) is longer than that of the second wave (about 1.5 units). A wavelength is represented by the Greek letter lambda (λ).

The number of wave cycles that pass through a specific point within a given time period is the frequency of the wave. It is represented by the Greek letter nu (n) and the unit of measurement is Hertz (Hz)—representing cycles per second. Since it has a shorter wavelength, the second wave has a higher frequency than the first wave.
The electromagnetic spectrum contains the familiar spectrum of visible light plus a wide array of nonvisible forms of radiation. The visible spectrum consists of different frequencies of light, corresponding to different colors. These are the colors you can see in a rainbow. Their order is the same in all rainbows, ranging from the lowest to highest frequency: red, orange, yellow, green, blue, indigo, and violet. The handy acronym ROY G. BIV can help you remember the order. All colors in the visible spectrum combine to form white light.

The remaining frequency ranges in the electromagnetic spectrum include radio waves, microwaves, infrared rays, ultraviolet rays, x–rays, and gamma rays.

In a vacuum, all waves in the electromagnetic spectrum travel at 2.998 × 108 meters/second — the speed of light.

Learn more about the electromagnetic spectrum.
Electromagnetic waves are categorized according to their wavelengths and frequencies. Wavelengths of different types of radiant energy can be smaller than the radius of an atom or can extend over hundreds of meters. The following table shows the different regions in the electromagnetic spectrum and their corresponding frequencies and wavelength
You now know that in the electromagnetic spectrum, radio waves have the longest wavelengths, ranging from a few inches to the length of a football field. These waves, invisible and completely undetectable to humans, have totally changed the way we live.

With the exception of light, you probably come across radio waves in your daily life more than any other wave from the electromagnetic spectrum. Broadcast TV signals are carried by radio waves. So are the signals for your cell phone, cordless phones, and of course your radio. Radio waves can transmit conversations, music, and pictures over millions of miles, all the way out into space! Let's find out how.
When an electric current passes through a length of a conductor, such as a radio transmitter, the electrons in the conductor gain energy and begin to oscillate, that is, move back and forth rapidly. The oscillating electrons produce both an electric field (E) and a magnetic field (B).

When the oscillating electrons move, the direction of these fields—and the forces they exert—change continuously. The constantly changing fields propagate as a radio wave. These waves are picked up by receiving antennas in television sets or radios. The oscillating fields cause electrons in antennas to oscillate in turn with the same frequency. These electrons generate an oscillating electric current in the antenna.
According to quantum mechanics, electrons oscillating in an atom do not give off waves continually. They must change energy levels to emit light. Nevertheless, classical electromagnetic waves, like radio waves, do share some common characteristics with light.

As was explained earlier, electrons in an atom emit light when they move from a higher energy level to a lower energy level. The frequency of the emitted light is directly proportional to the energy given off by the electrons. The higher the energy given off by the electron transition, the higher the frequency of the emitted light. This energy is expressed by the equation E=hv, where h represents Planck's constant, which is 6.626 × 10-34 Joule seconds (Js). This equation is known as Planck's law.

The frequency used in this equation is mathematically related to the wavelength of the radiation. The relationship between frequency and wavelength is the same for all types of electromagnetic radiation, from high energy gamma rays to long wavelength radio waves. It's the same relationship no matter how the radiation is generated.
In the radio wave simulation, you observed that when the frequency of the radio wave increased, its wavelength decreased. Since this pattern is the same for all electromagnetic waves, we can conclude that the wavelength and frequency of a wave are inversely proportional to each other: As frequency increases, wavelength decreases, and as frequency decreases, wavelength increases.

When the frequency and wavelength of an electromagnetic wave are multiplied, the product is equal to the speed of light, which is constant in a vacuum. This relationship is expressed by the following equation:
c = λv
In the equation, c denotes the speed of light, which is 2.998 × 108 meters/second. Lambda (λ) is the wavelength of the electromagnetic wave, and nu (ν) is its frequency. From this equation, we can derive the following equations to calculate the wavelength and frequency of a wave.
λ = c / ν and ν = c / λ
We can use this equation, c = λν, to calculate the frequency of a wave. Let's see how.

The wavelength of a specific photon in the infrared spectrum is
2 × 10-5 meters. Given that the speed of light is
2.998 × 108 meters/second, what would be the frequency of this infrared wave?
Solution:
Using the equation c = λν, we can derive ν = c / λ.
Replacing the values of c and λ in the above equation, we get
ν = 2.998 × 108 / 2 × 10-5 = 1.499 × 1013 Hz
We can use the same equation to calculate the wavelength of a wave. Let's see how.

The frequency of a wave in the ultraviolet region is 3.5 × 1015 Hz. Given that the speed of light is 2.998 × 108 meters/second, let's find the wavelength.
Solution:
Using the equation c = λν, we can derive λ = c / ν.
Replacing the values of c and n in the above equation, we get
λ = 2.998 × 108 / 3.5 × 1015 = 8.566 × 10-8 m
Visible light, which is necessary for our survival, is in fact only a small subset of the radiant energy that travels through space as electromagnetic waves. Electromagnetic radiation is made up of waves that are characterized by their amplitudes, wavelengths, and frequencies.

We're most familiar with the visible spectrum but, along with visible light, electromagnetic radiation also includes radio waves, microwaves, infrared rays, ultraviolet rays, x–rays, and gamma rays.

Electromagnetic waves with long wavelengths, such as radio waves, are produced by oscillating electrons. The frequency of the wave is directly proportional to the oscillation frequency of the electron. On the atomic scale, radiation is also emitted by alterations in quantum energy states. This happens when electrons change their energy states, moving to atomic orbitals with higher or lower energy values.