Which type of electromagnetic wave has the longest wavelength?
AGamma rays
BVisible light
CRadio waves
DX-rays
Radio waves have the longest wavelengths (from about 1 millimeter to hundreds of kilometers) and the lowest frequencies in the electromagnetic spectrum.
Question 2 True / False
All electromagnetic waves travel at the same speed in a vacuum.
TTrue
FFalse
Answer: True
In a vacuum, all EM waves — from radio to gamma — travel at the speed of light, approximately 3 × 10⁸ m/s.
Question 3 Short Answer
What determines whether an electromagnetic wave is classified as visible light, infrared, or ultraviolet?
Think about your answer, then reveal below.
Model answer: Its frequency (or equivalently, its wavelength). Visible light has frequencies between about 4.3 × 10¹⁴ Hz and 7.5 × 10¹⁴ Hz. Lower frequencies are infrared; higher frequencies are ultraviolet.
The electromagnetic spectrum is organized by frequency and wavelength. Each named region (radio, microwave, infrared, visible, ultraviolet, X-ray, gamma) corresponds to a specific range of frequencies.