Consider the following statements in respect of sound waves : I. The speed of sound waves decreases with an increase in temperature if the atmospheric pressure remains the same. II. The speed of sound waves increases with increasing humidity if the atmospheric pressure remains the same. III. The speed of sound waves is not affected by a change in atmospheric pressure, provided the temperature is kept constant. Which of the statements given above are correct?
- A.I and II only
- B.II and III only
- C.I and III only
- D.I, II and III
Correct answer
Explanation
The correct answer is B, II and III only. Sound travels faster in warmer air, so statement I is wrong, while II and III are right.
The speed of sound in a gas is v = √(γP/ρ). At a fixed temperature, raising the pressure raises the density in the same proportion, so P/ρ stays the same and the speed does not change, which is statement III. Raising the temperature lowers the density at the same pressure, so the speed rises, by roughly 0.6 m/s for each degree Celsius. Humid air is lighter than dry air because water vapour molecules weigh less than nitrogen and oxygen molecules, so sound also travels faster on a humid day.
A, I and II only, wrongly includes statement I and leaves out III.
C, I and III only, wrongly includes statement I and leaves out II.
D, I, II and III, wrongly accepts that heat slows sound down.
Exam tip: the speed of sound rises with temperature and humidity and does not depend on pressure; about 332 m/s in air at 0°C.
Practice Questions
View allConsider the following actions :
1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously
2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive
3. Detection of the tilt of the smartphone which results in the rotation of display between portrait and landscape mode
In how many of the above actions is the function of accelerometer required?
- A.Only one
- B.Only two
- C.All three
- D.None
Show answer
An accelerometer measures acceleration, including the pull of gravity, and each of the three actions depends on reading it. An accelerometer is a small sensor, today usually a MEMS (micro-electro-mechanical system) chip, that senses changes in speed and the direction of gravity.
Read the full explanation →Consider the following statements :
1. Carbon fibres are used in the manufacture of components used in automobiles and aircrafts.
2. Carbon fibres once used cannot be recycled.
Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
Show answer
Carbon fibre is widely used in cars and aircraft for its strength and low weight, and it can be recovered and recycled.
Read the full explanation →Which 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
Show answer
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 →