Which part of the electromagnetic spectrum has the longest wavelength?
- A.Radio waves
- B.Infrared rays
- C.Ultraviolet rays
- D.Gamma rays
Correct answer
Explanation
The correct answer is A, radio waves. Their wavelength runs from about a tenth of a metre up to many kilometres, which makes them the longest and therefore the lowest in frequency and energy of the whole spectrum; they are used in broadcasting, mobile telephony and radio astronomy. Option B is wrong because infrared lies between visible light and microwaves, from about 700 nanometres to a millimetre, so it is far shorter than radio waves. Option C is wrong because ultraviolet lies on the short side of visible light, from about 10 to 400 nanometres. Option D is wrong because gamma rays stand at the opposite end of the spectrum from radio waves, shorter than about 0.01 nanometre, with the highest frequency, the highest energy and the greatest penetrating power of all.
Read the full article: Electromagnetic Waves and the Spectrum: Exam Notes
Practice Questions
View allElectromagnetic waves were first produced and detected in the laboratory by which scientist?
- A.James Clerk Maxwell
- B.Heinrich Hertz
- C.Michael Faraday
- D.Guglielmo Marconi
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In 1887 he used a spark gap oscillator to generate waves and a loop with a gap to detect them, and he measured their wavelength and showed that they behaved like light in reflection and refraction, which confirmed the theory.
Read the full explanation →Which of the following statements about electromagnetic waves is correct?
- A.They are longitudinal waves and need a material medium
- B.They are transverse waves and can travel through vacuum
- C.They are deflected by a strong magnetic field
- D.Their speed in vacuum depends on their frequency
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In an electromagnetic wave the electric field, the magnetic field and the direction of propagation are mutually perpendicular, and because the wave is made of fields and not of vibrating particles it needs no medium, which is how sunlight crosses empty space while sound cannot.
Read the full explanation →Which electromagnetic radiation has the highest frequency and the greatest penetrating power?
- A.X-rays
- B.Gamma rays
- C.Microwaves
- D.Visible light
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They have the shortest wavelength of the spectrum and therefore the highest frequency and energy, and being uncharged and very energetic they pass through several centimetres of lead, which is why thick shielding is needed in radiotherapy rooms.
Read the full explanation →Which of the following arranges the radiations in order of increasing wavelength?
- A.Gamma rays, X-rays, ultraviolet, infrared, radio waves
- B.Radio waves, infrared, ultraviolet, X-rays, gamma rays
- C.X-rays, gamma rays, infrared, ultraviolet, radio waves
- D.Infrared, ultraviolet, radio waves, X-rays, gamma rays
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The spectrum in order of rising wavelength runs gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves, and the option follows that sequence with the visible and microwave bands left out.
Read the full explanation →X-rays were discovered by which scientist?
- A.Wilhelm Conrad Roentgen
- B.Henri Becquerel
- C.William Herschel
- D.Paul Villard
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In 1895 he noticed that a screen coated with a fluorescent salt glowed when a discharge tube was working nearby even though the tube was covered, and he called the unknown radiation X-rays; he received the first Nobel Prize in Physics in 1901 for the discovery.
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