Which one of the following is NOT an electromagnetic wave ?
- A.Light wave
- B.Radio wave
- C.Sound wave
- D.Micro wave
Correct answer
Explanation
The correct answer is C, Sound wave. Sound is a mechanical wave that needs a medium to travel, while the other three are electromagnetic waves.
Sound travels as a longitudinal wave of compressions and rarefactions in air, water or solids, which is why it cannot pass through a vacuum. Its speed in air is about 343 metres per second at 20°C. Electromagnetic waves are transverse oscillations of electric and magnetic fields; they need no medium and all travel at about 3 × 10^8 metres per second in a vacuum. In order of increasing frequency the electromagnetic spectrum runs radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
A is wrong: visible light is the part of the electromagnetic spectrum our eyes can detect.
B is wrong: radio waves are the longest-wavelength electromagnetic waves, used for broadcasting.
D is wrong: microwaves are electromagnetic waves between radio waves and infrared, used in ovens, radar and mobile networks.
Exam tip: sound needs a medium and is longitudinal; light, radio and microwaves cross a vacuum and are transverse.
Practice Questions
View allThe speed of the wind is measured by
- A.wind vane
- B.wind rose
- C.barometer
- D.anemometer
Show answer
An anemometer measures how fast the wind is blowing; its name comes from the Greek word anemos, meaning wind.
Read the full explanation →Brilliance of diamond is due to
- A.interference of light
- B.diffraction of light
- C.polarization of light
- D.total internal reflection of light
Show answer
Light that enters a cut diamond is reflected again and again inside it before it escapes, which makes the stone sparkle.
Read the full explanation →Which one of the following is NOT true for an electromagnetic wave ?
- A.Electromagnetic wave transports energy and momentum
- B.Electromagnetic wave can be polarized and reflected
- C.Electromagnetic wave is longitudinal
- D.Electromagnetic wave propagation is described by the varying electric and magnetic fields
Show answer
Electromagnetic waves are transverse, not longitudinal, so this statement is false. In an electromagnetic wave the electric field and the magnetic field oscillate at right angles to each other and both at right angles to the direction in which the wave travels.
Read the full explanation →Which one of the following frequency ranges is sensitive to human ears ?
- A.0-200 Hz
- B.20-20,000 Hz
- C.200-20,000 Hz only
- D.2,000-20,000 Hz only
Show answer
The normal human ear hears sound from about 20 hertz to 20,000 hertz, the audible range. Frequency, measured in hertz, is the number of vibrations per second, and it decides the pitch of a sound: the higher the frequency, the shriller the note.
Read the full explanation →The frequency of ultrasound waves is
- A.less than 20 Hz
- B.between 20 Hz and 2 kHz
- C.between 2 kHz and 20 kHz
- D.greater than 20 kHz
Show answer
Ultrasound is sound with a frequency above 20,000 Hz, the upper limit of human hearing. Humans hear sound between about 20 Hz and 20 kHz.
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