Electromagnetic Waves and Communication

Radio, visible light, and X-rays are the same kind of wave at different frequencies. They can cross empty space because changing electric and magnetic fields sustain one another.

This lesson supports Chapter 20 of Physics for Beginners. Keep the physical picture in view, write the units, and check the direction of every vector before trusting a calculation.

All electromagnetic waves travel at \(c\) in vacuum

In vacuum, \[c=f\lambda\] with \(c\approx3.00\times10^8\text{ m/s}\). Higher frequency means shorter wavelength. In matter, the wave can travel more slowly, but its frequency remains fixed as it crosses a boundary.

The spectrum is ordered by frequency

From low to high frequency, the usual order is radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma ray. Photon energy is \(E=hf\), so higher-frequency radiation has greater energy per photon. Ionizing ability becomes important at the high-frequency end.

Communication places information on a carrier

A transmitter modulates a carrier wave by changing amplitude, frequency, phase, or a digital code. An antenna launches the signal, a channel carries it, and a receiver recovers the information. Noise can corrupt a signal, so communication systems use filtering and error checks.

Worked example

A radio wave has frequency \(100\text{ MHz}=1.00\times10^8\text{ Hz}\). In vacuum, \(\lambda=c/f=(3.00\times10^8)/(1.00\times10^8)=3.00\text{ m}\).

Watch the idea in action

Khan Academy gives a focused explanation of the chapter’s central idea. Pause before each calculation and predict the next step on paper.

Practice questions

1. Write the vacuum wave relation.
2. What happens to wavelength when frequency increases in vacuum?
3. List the spectrum from radio through gamma rays.
4. How is photon energy related to frequency?
5. What is modulation?
6. Why do digital systems use error checks?

Answers

1. \(c=f\lambda\).
2. It decreases.
3. Radio, microwave, infrared, visible, ultraviolet, X-ray, gamma ray.
4. \(E=hf\), so energy increases with frequency.
5. Changing a carrier to encode information.
6. To detect or repair errors caused by noise.

Keep studying

Return to the Physics for Beginners learning hub, or move between the previous chapter lesson and the next chapter lesson. Each lesson opens in a new tab so the hub stays available.