Which of the following is incorrect ?

Options

A. To hear distinct beat the difference in the frequencies of two sources should be less than 10.
B. There is alternate variation in the intensity of sound during beat formation.
C. To hear distinct beats the difference in the frequencies of two sources should be more than 10.
D. Beat frequency is the difference between the frequencies of two sources

Answer

To determine which statement is incorrect regarding the concept of beats in sound waves, we will analyze each option step by step.

### Step 1: Understanding Beat Frequency
Beat frequency is defined as the difference in frequencies of two sound waves. If we have two sound sources with frequencies \( f_1 \) and \( f_2 \), the beat frequency \( f_b \) can be expressed as:
\[ f_b = |f_2 - f_1| \]

### Step 2: Distinct Beats Hearing Threshold
To hear distinct beats, the difference in frequency between the two sound sources must be less than 10 Hz. This is because our auditory system can only distinguish sounds that are separated by a certain time interval. If the frequency difference is greater than 10 Hz, the beats become too rapid for our ears to distinguish.

### Step 3: Evaluating the Statements
1. **Statement A**: "To hear distinct beats, the frequencies of the two sources should be less than 10 Hz."
- This statement is **correct**. We can distinctly hear beats when the frequency difference is less than or equal to 10 Hz.

2. **Statement B**: "There is an alternate variation in the intensity of sound during beat formation."
- This statement is **correct**. When two sound waves interfere, they create a pattern of constructive and destructive interference, leading to variations in intensity.

3. **Statement C**: "To hear distinct beats, the difference in the frequency of the two sources should be more than 10 Hz."
- This statement is **incorrect**. As established, the difference must be less than or equal to 10 Hz for distinct beats to be heard.

4. **Statement D**: "Beat frequency is the difference between the frequencies of two sources."
- This statement is **correct**. The definition of beat frequency is indeed the absolute difference between the two frequencies.

### Conclusion
Based on the analysis, the incorrect statement is **Statement C**: "To hear distinct beats, the difference in the frequency of the two sources should be more than 10 Hz."

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