A source of sound of frequency 600 Hz is placed inside water. The speed of sound in water is 1500 m/s and in air it is 300 m/s. The frequency of sound recorded by an observer in air is :

Question

Accepted Answer

The correct answer to the question is Option 3: 600 Hz. Here is a detailed explanation supporting this answer:

1. **Explanation for Option 3 (600 Hz):**
   - The frequency of a sound wave is determined by the source of the sound and remains constant regardless of the medium through which it travels. This is because frequency is a property of the source, not the medium.
   - In this scenario, the source of sound has a frequency of 600 Hz and is placed inside water. When the sound travels from water to air, its speed changes due to the different properties of the two media, but its frequency remains unchanged.
   - Therefore, an observer in air will record the same frequency of 600 Hz, as frequency does not change when sound waves move from one medium to another.

2. **Explanation for why other options are incorrect:**
   - **Option 1 (3000 Hz):** This option suggests that the frequency increases when the sound moves from water to air. However, frequency is not affected by the change in medium; only the speed and wavelength change. Thus, 3000 Hz is incorrect.
   - **Option 2 (1500 Hz):** This option might be mistakenly chosen if one assumes that the frequency changes proportionally with the speed of sound in different media. However, as stated, frequency remains constant at 600 Hz, making 1500 Hz incorrect.
   - **Option 4 (120 Hz):** This option suggests a decrease in frequency, which is not possible when sound transitions between media. The frequency remains constant at 600 Hz, so 120 Hz is incorrect.

In conclusion, the frequency of sound recorded by an observer in air is 600 Hz, as frequency is a property of the source and does not change with the medium. This supports Option 3 as the correct answer.