Which among the following is true for propagation of sound waves ?
- A.Sound can travel in vacuum and it is a transverse wave in air.
- B.Sound cannot travel in vacuum and it is a longitudinal wave in air.
- C.Sound can travel in vacuum and it is a longitudinal wave in air.
- D.Sound cannot travel in vacuum and it is a transverse wave in air.
Correct answer
Explanation
The correct answer is B, sound cannot travel in vacuum and it is a longitudinal wave in air. Sound is a mechanical wave, so it needs a medium, and in air its particles vibrate along the direction of travel.
A sound wave moves as a series of compressions and rarefactions: the air particles are pushed together and pulled apart along the line in which the wave travels, which makes it longitudinal. With no particles to pass the vibration on, sound cannot cross a vacuum; the classic bell-jar experiment shows a ringing bell fall silent as the air is pumped out. In air at room temperature sound travels at about 343 m/s, faster in water and faster still in steel. Light, an electromagnetic wave, needs no medium and is transverse.
A and C are wrong because sound cannot travel in a vacuum. D is wrong because sound in air is longitudinal, not transverse; air cannot carry transverse waves.
Exam tip: sound = mechanical, longitudinal, needs a medium; light = electromagnetic, transverse, travels through vacuum.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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