AS Level Physics · Waves. A short explanation of the idea, the rules to remember, the mistake to avoid, a worked example and practice questions with answers.
All electromagnetic waves are transverse waves. In free space (a vacuum) they all travel at the same speed, c = 3.00 × 108 m s−1. They do not need a medium.
The regions of the spectrum differ only in wavelength and frequency. In order of decreasing wavelength they are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and γ-rays. Because c is fixed, a shorter wavelength always means a higher frequency.
You must know the rough wavelength range of each region, and that the eye sees only wavelengths from about 400 nm (violet) to 700 nm (red). The ranges of X-rays and γ-rays overlap.
Students mix up the two ends of the spectrum. Radio waves have the longest wavelength and lowest frequency; γ-rays have the shortest wavelength and highest frequency.
Answer: Infrared (wavelength 5.0 × 10−6 m)
Try each one, then open the answer.
Answer: C. f = c/λ = 3.0 × 108 ÷ 3.0 = 1.0 × 108 Hz (100 MHz, FM radio).
Answer: C. From shortest to longest: γ-rays, X-rays, ultraviolet, visible, infrared, microwaves, radio waves.
Answer: D. λ = c/f = 3.00 × 108 ÷ 1.0 × 1015 = 3.0 × 10−7 m = 300 nm. This is shorter than 400 nm, the violet end of the visible range, so it is ultraviolet.
← Doppler effect for sound wavesPolarisation →All rules on one pageStuck? Ask a question