Ultrasonic and Infrasonic Waves: The sound having frequency 20 Hz to 20 KHz is called audible sound Human ear cannot hear sound of frequencies lying outside this range. The limits of audibility of sound vary from individual. Generally the upper limit decreases with increase of age of individual, usually and people can not hear sound of frequency more than 15 kHz.
Sound of frequencies below 20 Hz are called infrasonics, while frequencies beyond 20 kHz are called ultrasonics. Ultrasonics can be heard by dogs, cat bats etc. Bats detect the path by means of ultrasonics. Ultrasonics can be used for diagnosis of tumour and other abnormalities within our body. This is known as ultrasonography. Ultrasonics are used to curve various diseases and to measure depth of oceans to detect submarines.
If speed of infrasonics, a audible and ultrasonics waves are `v_(i),v_(a)andv_(u)` then

Options

A. `v_(i)gtv_(a)gtv_(u)`
B. `v_(i)=v_(a)=v_(u)`
C. `v_(i)ltv_(a)ltv_(u)`
D. `v_(i)gtv_(a),v_(u)gtv_(a)`

Answer

To solve the problem regarding the relationship between the speeds of infrasonic, audible, and ultrasonic waves, we can follow these steps:

### Step 1: Understand the Definitions
- **Infrasonic Waves**: Frequencies below 20 Hz.
- **Audible Waves**: Frequencies between 20 Hz and 20 kHz (typically around 15-16 kHz for older individuals).
- **Ultrasonic Waves**: Frequencies above 20 kHz.

### Step 2: Recall the Wave Speed Formula
The speed of a wave (v) is given by the formula:
\[ v = \lambda \times f \]
where \( \lambda \) is the wavelength and \( f \) is the frequency of the wave.

### Step 3: Analyze the Relationship Between Frequency and Wavelength
- For a given medium, the speed of sound is generally constant. Therefore, if the frequency increases, the wavelength must decrease to maintain the same speed.
- **Ultrasonic waves** have the highest frequency, which means they have the shortest wavelength.
- **Audible waves** have a medium frequency and thus a medium wavelength.
- **Infrasonic waves** have the lowest frequency, which corresponds to the longest wavelength.

### Step 4: Compare the Speeds
Since the speed of sound is constant in a given medium, the speeds of infrasonic, audible, and ultrasonic waves can be compared:
- \( v_i \) (speed of infrasonic) = \( v_a \) (speed of audible) = \( v_u \) (speed of ultrasonic).

### Conclusion
The order of the speeds of the three types of waves is:
\[ v_i = v_a = v_u \]

### Final Answer
Thus, the order of the speeds is:
\[ v_i = v_a = v_u \]

---