Wi-Fi lets phones, laptops, and game systems share information without wires by using radio waves. A router takes data from the internet, breaks it into packets, and sends those packets through the air as carefully shaped electromagnetic signals. Your device receives the signals, decodes the data, and rebuilds the video, image, or webpage you requested.
This matters because the same physics that carries a cat video also explains weak signals, lag, interference, and dead zones in a home.
Key Facts
- Wi-Fi is electromagnetic radiation, the same kind of wave family as visible light but with much lower frequency.
- Common Wi-Fi bands are near f = 2.4 GHz and f = 5 GHz, where 1 GHz = 1,000,000,000 Hz.
- Wave speed in air is approximately c = 3.0 x 10^8 m/s, and wavelength is λ = c/f.
- A 2.4 GHz Wi-Fi signal has wavelength λ ≈ 0.125 m, while a 5 GHz signal has wavelength λ ≈ 0.060 m.
- Modulation changes a carrier wave so it can carry information, and QAM encodes data by changing both amplitude and phase.
- OFDM splits data across many closely spaced subcarriers, which helps Wi-Fi resist echoes and interference.
Vocabulary
- Packet
- A packet is a small labeled chunk of digital data sent across a network and reassembled at the destination.
- Carrier wave
- A carrier wave is a steady radio wave that is modified to carry information.
- Modulation
- Modulation is the process of changing a wave property such as amplitude, frequency, or phase to encode data.
- QAM
- QAM, or quadrature amplitude modulation, is a method that encodes multiple bits by changing both the amplitude and phase of a signal.
- OFDM
- OFDM, or orthogonal frequency division multiplexing, is a technique that divides data among many subcarriers to improve reliable transmission.
Common Mistakes to Avoid
- Thinking Wi-Fi is the same as the internet: Wi-Fi is only the local wireless link between your device and router, while the internet is the larger network beyond your home.
- Assuming higher frequency always means better Wi-Fi: 5 GHz can carry data quickly, but 2.4 GHz often travels farther and passes through walls more easily.
- Ignoring wavelength when placing a router: walls, metal objects, and water can absorb or reflect radio waves, which can create weak spots and interference patterns.
- Believing a video is sent as pictures through the air: Wi-Fi sends encoded bits in packets, and the device reconstructs the compressed video frames after decoding them.
Practice Questions
- 1 Calculate the wavelength of a 2.4 GHz Wi-Fi signal using λ = c/f with c = 3.0 x 10^8 m/s.
- 2 A router sends data at 120 megabits per second. How long would it take to send a 60 megabit video file, ignoring overhead and errors?
- 3 A laptop has a stronger connection in the same room as the router than behind two thick walls. Explain using absorption, reflection, and frequency why the signal changes.