Which of the following pairs of coils has zero coupling constant?

Options

A.
B.
C.
D. All of these

Answer

To solve the question regarding which pair of coils has a zero coupling constant, we need to understand the concept of mutual inductance and coupling constant. The coupling constant (L) between two coils is determined by the magnetic flux produced by one coil that links with the other coil.

### Step-by-Step Solution:

1. **Understanding Coupling Constant**: The coupling constant (L) between two coils is defined as the ratio of the magnetic flux (Φ) linking one coil due to the current (I) in the other coil. Mathematically, it is expressed as:
\[ L = \frac{\Phi}{I} \]

2. **Identifying Zero Coupling Constant**: A zero coupling constant indicates that there is no magnetic flux linking the two coils. This can occur when the magnetic field produced by one coil does not intersect or influence the other coil at all.

3. **Analyzing the Options**: We need to evaluate each pair of coils given in the options to determine which pair has zero coupling constant.

4. **Evaluating Option B**: According to the video solution, option B is suggested to be the correct answer. In this pair, the magnetic field produced by coil C1 is parallel to coil C2. Since the magnetic field lines do not pass through coil C2, the flux linking coil C2 is zero.

5. **Conclusion**: Therefore, since there is no magnetic flux linking coil C2 from coil C1, the coupling constant for this pair is zero. Hence, option B is the correct answer.

### Final Answer:
The pair of coils that has a zero coupling constant is **Option B**.