Assertion : Wave number is the number of waves per units length.
Reason : Wave number `=(1)/(lambda)`.

Options

A. If both Assertion and Reason are true and the Reason is correct expanation of the Assertion.
B. If both Assertion and Reason are true but the Reason is not correct expanation of the Assertion.
C. If Assertion is true, but the Reason is false.
D. If Assertion is false but the Reason is true.

Answer

To solve the assertion and reason question, we will analyze both statements step by step.

### Step 1: Understanding the Assertion
The assertion states that "Wave number is the number of waves per unit length."
- **Wave number (k)** is defined as the number of wavelengths in a unit distance. It quantifies how many complete waves fit into a given length.

### Step 2: Understanding the Reason
The reason states that "Wave number = 1/λ."
- Here, λ (lambda) represents the wavelength, which is the distance over which the wave's shape repeats. The wave number (k) is indeed defined as the reciprocal of the wavelength:
\[ k = \frac{1}{\lambda} \]
This means that for a given wavelength, the wave number tells us how many wavelengths fit into one unit of length.

### Step 3: Analyzing the Relationship
Now we can connect the assertion and reason:
- Since wave number is defined as the number of waves per unit length, and since we have established that \( k = \frac{1}{\lambda} \), it follows that the assertion is correct because the wave number indeed represents the number of waves in a unit length.

### Step 4: Conclusion
Both the assertion and the reason are true, and the reason provides a correct explanation for the assertion.

### Final Answer:
- Both the assertion and the reason are true, and the reason correctly explains the assertion.

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