Sound Test - 31

Below are the answers and the corresponding explanations.

(a) True. Sound requires a medium to travel through. Since vacuum is devoid of any medium, sound cannot travel through it.

(b) False. The number of oscillations per second of a vibrating object is known as its frequency. Time period is the time
required to complete one oscillation.

(c) False. Loudness of a sound is proportional to the square of the amplitude of its vibration. When the amplitude of
vibration of a sound is large, the sound is very loud. The sound is feeble for small amplitude.

(d) True. Humans cannot hear sounds of all frequencies. Human can hear a sound whose frequency falls in the range of
20 Hz - 20,000 Hz. The sound having frequency out of this range is inaudible to humans.

(e) False. The pitch of a sound is proportional to its frequency. As the frequency of vibration increases,
the pitch of the sound also increases and vice versa. A sound is said to be high pitched if its frequency of vibration is high
and is low pitched for a small frequency of vibration.

(f) False. Unwanted or unpleasant sounds are known as noise. Sounds that are melodious and pleasing to ear are known as music.

(g) True. Unwanted or unpleasant sounds are known as noise. If one is subjected to loud unpleasant sound
continuously for a long time, then it may cause temporary hearing impairment.

Answer is A.

The intensity or loudness of a sound depends upon the extent to which the sounding body vibrates, i.e., the amplitude of vibration. A sound is louder as the amplitude of vibration is greater. Loudness is measured in units called decibels.

Answer is C.

The top of the tabla drum is covered with a stretched, layered leather membrane held in place by leather braces. The wooden pegs between the braces and the drum adjust the tension in the braces, thus controlling the pitch of the instrument.
Hence, to increase the pitch of the sound produced the player tightens the skin by stretching the string around it.

The answer is B.

Amplitude is the maximum distance covered by an oscillating body. To complete one oscillation, the body has to start from the mean position, then goes to the maximum distance on one side, then comes back to the mean position, then goes to the maximum position on the other side, and finally comes back to the mean position.

Time Period (T) is the number of seconds per waveform, or the number of seconds per oscillation.  It is clear that frequency and period are reciprocals. 
In this case, A bicycle wheel spins 25 times in 5 seconds. 
That is, the frequency is given as $$f=\frac { 25 }{ 5 } =5Hz$$.
Time period = $$\frac { 1 }{ f } =\frac { 1 }{ 5 } =0.20s$$
Hence, the frequency is 5 Hz and the time period is 0.20 seconds.

The maximum amount that a particle moves away from its rest position is called amplitude.
Amplitude is the maximum displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position. It is equal to one-half the length of the vibration path. 
For a transverse wave, such as the wave on a plucked string, amplitude is measured by the maximum displacement of any point on the string from its position when the string is at rest. For a longitudinal wave, such as a sound wave, amplitude is measured by the maximum displacement of a particle from its position of equilibrium. 

Answer is B.

Sound needs something to travel through to get from one place to another. In the space, since there is no air, sound cannot travel above the surface. So, there are no sounds in the space. 
The space has no air because its gravity is too weak to hold an atmosphere. Hence, if an enemy spaceship exploded 'they will not hear anything as there is no medium for sound to travel, but they can see the explosion because light can travel through space as light needs no medium to travel.
Renu is correct.

Answer is A.

When tuning a violin, a string is tightened which means that the length of the string is shortened.
When the length of a string is changed, it will vibrate with a different frequency. Shorter strings have higher frequency and therefore higher pitch. When a musician presses his finger on a string, he shortens its length. The more fingers he adds to the string, the shorter he makes it, and the higher the pitch will be. That is, higher frequency. 
Hence, the statement is true.

Hint: The time period is the inverse of the frequency.

Step – 1: Get relationship between frequency and time period

The time period is shown as,

So, $$time\ period = \dfrac{1}{frequency}$$

Step – 2: Put value in the equation 

Here, mosquito generates average rate of 500 vibrations per second. So, frequency will be 500.

$$time\ period = \dfrac{1}{frequency}$$

$$= \dfrac{1}{500}$$

 $$= 0.002\ second$$

$$Answer:$$

Hence, option A is the correct answer.

Frequency is inverse of the time period ,