A lift is often surrounded by metal. Conducting materials interact strongly with radio-frequency electromagnetic waves and can reflect or absorb much of the signal. This shielding effect reduces the strength of waves travelling between your phone and a mobile mast. Thick walls and the lift shaft can weaken the connection further. If the signal arriving at the phone becomes too weak compared with noise and interference, the device may lose its connection. The same basic physics is used deliberately in a Faraday cage, where conducting material shields an interior from external electric fields and electromagnetic signals.

The useful part of this physics is that it helps people predict and design real things. Engineers often begin with the same simplified model used in school, test where it works, then add more detail when measurements show that the real situation is more complicated.

Waves transfer energy and information without transferring matter from source to receiver overall. Frequency tells us how many oscillations pass each second, wavelength is the spacing between matching points, and wave speed links them through v = fλ. Different frequencies interact with materials differently, which is why engineers can choose particular parts of the electromagnetic spectrum—or particular sound frequencies—for sensing, communication, heating or imaging.