During superposition of two waves of nearly equal frequencies , beat frequency is defined as the

Options

A. Sum of frequencies of interfering waves
B. Number of times the resultant intensity becomes maximum or minimum is one second
C. Average of frequencies of interfering waves
D. Number of times the resultant amplitude becomes maximum or minimum in one second .

Answer

To solve the question regarding the definition of beat frequency during the superposition of two waves of nearly equal frequencies, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Wave Superposition**:
- When two waves with frequencies \( \nu_1 \) and \( \nu_2 \) are superimposed, they interfere with each other. The resulting wave is a combination of the two.

**Hint**: Remember that superposition refers to the addition of two or more waves to form a resultant wave.

2. **Defining Beat Frequency**:
- Beat frequency is defined as the frequency of the amplitude variations (maxima and minima) of the resultant wave formed by the interference of the two waves.

**Hint**: Focus on how the interference of two waves leads to variations in amplitude over time.

3. **Mathematical Expression**:
- The beat frequency \( f_{beat} \) can be mathematically expressed as:
\[ f_{beat} = |\nu_1 - \nu_2| \]
- This means that the beat frequency is the absolute difference between the two frequencies.

**Hint**: The absolute value indicates that we are interested in the magnitude of the difference, regardless of which frequency is higher.

4. **Analyzing the Options**:
- Option A states that beat frequency is the sum of the frequencies. This is incorrect.
- Option B states that it is the number of times the resultant intensity becomes maxima or minima in one second. This is misleading because it should refer to amplitude, not intensity.
- Option C suggests that it is the average of the frequencies. This is also incorrect.
- Option D correctly states that it is the number of times the resultant amplitude becomes maximum or minimum in one second.

**Hint**: Carefully evaluate each option based on the definition and properties of beat frequency.

5. **Conclusion**:
- The correct definition of beat frequency is that it is the number of times the resultant amplitude becomes maximum or minimum in one second, which corresponds to option D.

**Hint**: Always relate the definitions to the physical phenomena they describe.

### Final Answer:
The beat frequency is defined as the number of times the resultant amplitude becomes maximum or minimum in one second, which corresponds to option D.