Which one of the following phenomena CANNOT be exhibited by sound waves ?
- A.Reflection
- B.Refraction
- C.Interference
- D.Polarisation
Correct answer
Explanation
The correct answer is D, Polarisation. Sound in air is a longitudinal wave, and only transverse waves can be polarised.
Polarisation means restricting the vibrations of a wave to a single plane. That is possible only when the particles or fields vibrate at right angles to the direction the wave travels, as in light and other electromagnetic waves. In a sound wave travelling through air, the particles vibrate back and forth along the direction of travel, forming compressions and rarefactions, so there is no sideways vibration to filter. Polarisation is therefore the test that separates transverse waves from longitudinal ones.
A is wrong: sound reflects off hard surfaces, which is why we hear echoes and why SONAR works.
B is wrong: sound bends when it passes between layers of air at different temperatures, which is why it carries farther on cold nights.
C is wrong: two sound waves can combine to give louder and softer regions, and beats are an example of this.
Exam tip: Reflection, refraction, interference and diffraction happen to all waves; polarisation only to transverse waves such as light.
Practice Questions
View allWhich one of the following cell organelles contains DNA?
- A.Golgi apparatus
- B.Mitochondrion
- C.Lysosome
- D.Endoplasmic reticulum
Show answer
Mitochondria carry their own small, circular DNA and their own ribosomes. Mitochondria are the powerhouses of the cell, where aerobic respiration makes ATP.
Read the full explanation →Which set of vegetables is underground stem or modified stem of a plant?
- A.Potato, artichoke, round gourd
- B.Onion, garlic, carrot
- C.Potato, onion, garlic
- D.Potato, garlic, turnip
Show answer
All three are underground modified stems: the potato is a stem tuber, and onion and garlic are bulbs. A stem can be told from a root by its nodes and buds.
Read the full explanation →A sound wave having frequency of 300 Hz is travelling in an unknown medium. Its wavelength is not known. It travels a distance equal to 150 times its wavelength in time t. The value of t is :
- A.0.5 s
- B.1 s
- C.1.5 s
- D.2 s
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A wave moves forward by one wavelength in each cycle, so 150 wavelengths take 150 cycles, and 150 cycles at 300 per second take half a second.
Read the full explanation →A body floats in a liquid if the buoyant force is :
- A.equal to its weight.
- B.less than its weight.
- C.greater than its weight.
- D.zero.
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A floating body is in equilibrium, so the upward buoyant force exactly balances its weight. By Archimedes' principle, a body in a liquid is pushed up by a force equal to the weight of the liquid it displaces.
Read the full explanation →Which of the following are the different parts of a human brain ?
- A.Forefront brain, Standard brain and Hind brain
- B.Fore brain, Median brain and Rear brain
- C.Fore brain, Mid brain and Hind brain
- D.Precursor brain, Mean brain and Hind brain
Show answer
These are the three main divisions of the human brain. The fore brain is the largest part.
Read the full explanation →