The direction of poynting vector represents

Options

A. The direction of electric field
B. The direction of magnetic field
C. The direction of propagation of EM wave
D. The direction opposite to the propagation of EM wave

Answer

To solve the question regarding the direction of the Poynting vector, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Poynting Vector**:
The Poynting vector (denoted as **S**) represents the directional energy flux (the rate of energy transfer per unit area) of an electromagnetic field.

2. **Mathematical Expression**:
The Poynting vector is given by the formula:
\[ \mathbf{S} = \frac{1}{\mu} \mathbf{E} \times \mathbf{B} \]
where:
- **E** is the electric field vector,
- **B** is the magnetic field vector,
- **μ** is the permeability of the medium.

3. **Direction of the Poynting Vector**:
The direction of the Poynting vector is determined by the cross product of the electric field and the magnetic field. The result of a cross product is always perpendicular to the plane formed by the two vectors.

4. **Relation to EM Wave Propagation**:
In electromagnetic waves, the electric field **E** and magnetic field **B** oscillate perpendicular to each other and also perpendicular to the direction of wave propagation. Therefore, the Poynting vector, which indicates the direction of energy flow, points in the direction of wave propagation.

5. **Evaluating the Options**:
- **Option 1**: Direction of electric field - Incorrect.
- **Option 2**: Direction of magnetic field - Incorrect.
- **Option 3**: Direction of propagation of EM wave - Correct.
- **Option 4**: Direction opposite to the propagation of EM wave - Incorrect.

6. **Conclusion**:
The correct answer is that the direction of the Poynting vector represents the direction of propagation of the electromagnetic wave.

### Final Answer:
The direction of the Poynting vector represents the direction of propagation of the electromagnetic wave.

---