Sound — Set 6
Physics · ध्वनि · Questions 51–60 of 60
The reference intensity I0 used in air for the decibel scale is commonly taken as?
Correct Answer: A. 0 W/m^2
The reference intensity I0 in air is commonly 1 × 10^-12 watts per square meter. It is close to the threshold of hearing for a typical young person. Using this reference allows sound levels to be compared consistently.
An increase of 10 dB in sound level corresponds to an intensity ratio of?
Correct Answer: C. 10 times
Decibel level uses a logarithmic scale based on intensity ratios. A 10 dB increase means the intensity becomes 10 times larger. A 20 dB increase would therefore mean 100 times intensity.
If two tuning forks of frequencies f1 and f2 are sounded together, the beat frequency is?
Correct Answer: D. |f1 - f2|
Beat frequency equals the absolute difference between the two frequencies. This gives how many loudness maxima occur per second. Musicians use slow beats to fine tune instruments to the same frequency.
For an open organ pipe of length L, the fundamental frequency is?
Correct Answer: B. f = v/4L
In an open pipe, the fundamental mode fits half a wavelength in the length. That means λ equals 2L, so f equals v divided by 2L. Higher modes are integer multiples of this fundamental frequency.
For a pipe closed at one end and open at the other, the fundamental frequency is?
Correct Answer: C. f = v/4L
In a closed pipe, the fundamental mode fits a quarter wavelength in the length. That means λ equals 4L, so f equals v divided by 4L. This makes the fundamental frequency lower than an open pipe of the same length.
A pipe closed at one end supports which harmonics prominently?
Correct Answer: D. Only odd harmonics
A closed pipe has a node at the closed end and an antinode at the open end. This boundary condition allows only odd multiples of the fundamental frequency. So the 3rd, 5th, and 7th harmonics are present while even ones are missing.
Mach number is defined as?
Correct Answer: A. Speed of object divided by speed of sound
Mach number compares an object's speed to the speed of sound in the same medium. It is defined as object speed divided by sound speed. Mach 2 means the object is moving at twice the speed of sound.
The eardrum is also known as the?
Correct Answer: C. Tympanic membrane
The eardrum is called the tympanic membrane. It vibrates when sound waves strike it. These vibrations are passed onward to the middle ear bones.
Human hearing is generally most sensitive around frequencies of?
Correct Answer: B. About 20–40 MHz
The ear is most sensitive to sounds in the few kilohertz range. This is commonly around about 2 to 4 kHz for many people. Many speech sounds fall near this region, helping communication.
For a point sound source in free space, intensity generally varies with distance r as?
Correct Answer: D. I ∝ 1/r^2
Sound energy from a point source spreads over a larger area as distance increases. The area of a sphere grows as r squared, so intensity falls as 1 over r squared. Doubling distance therefore reduces intensity to about one quarter in ideal conditions.