Which one of the following radiations has longer wavelength?
- (a)X-rays
- (b)Ultraviolet
- (c)Micro Wave
- (d)Infra-red
Correct — C, microwave. In the electromagnetic spectrum, wavelength increases (and frequency decreases) in the order X-rays, then ultraviolet, then visible, then infrared, then microwaves, then radio waves. Of the four options, microwaves have by far the longest wavelength — from about a millimetre up to tens of centimetres — longer than infrared, ultraviolet and X-rays.
- (a)X-rays — X-rays have the shortest wavelength of the four (roughly 0.01 to 10 nanometres) and the highest energy — the opposite of what is asked.
- (b)Ultraviolet — Ultraviolet wavelengths (about 10 to 400 nanometres) are shorter than infrared and far shorter than microwaves.
- (d)Infra-red — Infrared (about 700 nanometres to 1 millimetre) has a longer wavelength than UV and X-rays, but it is still shorter than microwaves, so it is not the longest here.
The electromagnetic spectrum arranges radiation by wavelength and frequency. Radio waves have the longest wavelength and gamma rays the shortest. Among the four in this question, microwave is the longest, followed by infrared, then ultraviolet, then X-ray.
A handy order of increasing wavelength is: gamma, X-ray, ultraviolet, visible, infrared, microwave, radio. Wavelength and frequency are inversely related through the relation that speed equals frequency times wavelength, and photon energy is proportional to frequency, so the longest-wavelength radiation also has the lowest frequency and energy.
- Order of increasing wavelength: gamma, then X-ray, then UV, then visible, then infrared, then microwave, then radio.
- Among X-ray, ultraviolet, infrared and microwave, the microwave has the longest wavelength.
- Wavelength and frequency are inversely related (speed equals frequency times wavelength).
- Longer wavelength means lower frequency, which means lower photon energy.
Wavelength grows X-ray to UV to infrared to microwave; the microwave is the longest of the four.
- Confusing the wavelength order with the energy or frequency order — they run in opposite directions.
- Assuming X-rays, being 'powerful', must have a long wavelength; in fact they have the shortest of the four.
Asked as which radiation has the longest or shortest wavelength (or the highest energy or frequency), testing the order of the electromagnetic spectrum.
Which one of the following types of waves are used in a night vision apparatus?
- (a) Radio waves
- (b) Microwaves
- (c) Infra-red waves
- (d) None of the above
Answer(c) Infra-red waves
Same electromagnetic-spectrum knowledge. There you must know that infrared is the band used in night-vision devices; here you place infrared and microwave in the spectrum to see that the microwave has the longer wavelength.
Consider the two statements given below: Statement-1: Infrared waves are also called heat waves. Statement-2: Water molecules readily absorb infrared waves. Select the correct answer using the code given below:
- (a) Both the statements are individually true and Statement-2 is the correct explanation of Statement-1.
- (b) Both the statements are individually true, but Statement-2 is not the correct explanation of Statement-1.
- (c) Statement-1 is true, but Statement-2 is false.
- (d) Statement-2 is true, but Statement-1 is false.
Answer(a) Both the statements are individually true and Statement-2 is the correct explanation of Statement-1.
Same electromagnetic-spectrum family — the infrared band. There the focus is on infrared as heat waves absorbed by water; here infrared is one of the four radiations you rank by wavelength, sitting between ultraviolet and microwave.
- practice — not a real PYQ
Which of the following electromagnetic radiations has the shortest wavelength?
- (a)X-rays
- (b)Ultraviolet
- (c)Infrared
- (d)Microwave
Answer(a) X-rays — they have the shortest wavelength and the highest energy of the four.
- practice — not a real PYQ
In the electromagnetic spectrum, which of the following has a higher frequency than visible light?
- (a)Infrared
- (b)Microwave
- (c)Ultraviolet
- (d)Radio waves
Answer(c) Ultraviolet — it has a shorter wavelength and higher frequency than visible light.