Electromagnetic radiation and light

Light is a electromagnetic radiation. It travels in wave form with infinite number of energy pockets called “photons”. As we all know, a wave form has amplitude, frequency and wave length as its main parameters.

Main Parameters:

  1. Amplitude
  2. Frequency
  3. Cycle
  4. Wavelength
Rays of Light
Electromagnetic wave


Amplitude: The maximum displacement of a periodic wave.
Frequency: The number of occurrences within a given time period. (No. of cycles per second – hertz).
Cycle: It is defined as the single complete execution of a periodically repeated process.
Wavelength: It is simply the length of one complete cycle. (Normally the range varies from nanometer to kilometer)

These parameters are indeed defines or categorizes the broad spectrum of electromagnetic radiation which includes visible light.

The speed of all electromagnetic radiation or EM waves in vacuum is 299,792,458 meters per second. So no matter what the parameters are, if waves start from a point at a time, they will reach the other point at the same time.

Relation between frequency and wavelength:

Speed (Velocity) of EM wave = Wavelength • Frequency

Since the speed of EM wave is constant, the wavelength is inversely proportional to the frequency and vice versa.
Take this example. Let’s say, the speed of light is 20 and the initial value for wavelength and frequency are 5 and 4 respectively.

By equation, 20 = 5 • 4, Changing wavelength and frequency,

20 = 2 • 10
20 = 10 • 2

You can see that, from the above example, if the wavelength reduces the frequency increases to equal the speed of light on other side and vice versa.

Spectrum of electromagnetic radiation

Note: These values are approximate only. These is no exact boundary defined for each category. The limits extend beyond the values shown here.

The above picture shows the spectrum of electromagnetic radiation which includes visible light.

The speed of electromagnetic radiation or EM waves in vacuum is 299,792,458 meters per second. Since the light is a kind of EM wave, it has the same speed. Even though the speed is same, the factors like “how far it can travel” and “what it can travel through” majorly depends upon the wavelength and frequency. The amplitude tells us how strong the wave is. i.e. The high amplitude visible light will look brighter than a low amplitude visible light even if they have same wavelength and frequency.

Here are some examples:

1. The light wave cannot travel through a solid rock or a concrete building. That’s how we get shadows. Shadow is actually the absence of light. But at the same time, light can travel through the glass. This is because the property of glass itself like density.
2. Gamma-rays are high energy waves. They can travel through solid rock, low density concrete or anything. But it struggles to travel through high density materials like lead etc. That’s why lead and high density concretes are used as insulators for many radiation protection purposes.

Wave propagation:

For example, Imagine dropping a big stone into a pond of water. The waves are generated at the impact point and start moves outwards in all directions. The energy of the wave at the impact point is very high and as it move outwards its energy diminishes at constant rate. At some point of time, you can’t even see the wave traveling. This is in the case of water wave, a category of mechanical waves.

Now just take the theme and apply it to EM waves. The strength of the wave diminishes at constant rate as it travels and is defined by the inverse-square law.

Inverse-square law  explained:

In general, the inverse-square law states that the power intensity of an expanding wave is inversely proportional to the square of the distance from the source.
i.e. Intensity 1 / Distance2

The above picture explains this phenomenon and you can see that the intensity of the blue light is reducing as the distance of the screen from the light source increases.

The actual formula for intensity is “power divided by area”.
i.e. I = P / A

Since the radiation expands in all directions, it forms a sphere.

That’s all for this topic. I hope this helped you. Click here to read other topics or search your topic below.

You can read some unmatched stuffs about EM radiation here at NASA.