Ground waves are polarised

Options

A. parallel to the earth's surface
B. normal to the earth's surface
C. at an angle `45^(@)` from earth's surface
D. in any direction

Explanation

To solve the question regarding the polarization of ground waves, we can break it down into a series of logical steps:

### Step-by-Step Solution:

1. **Understanding Ground Waves**: Ground waves are electromagnetic waves that travel along the surface of the Earth. They are used in communication systems, especially for long-range transmission.

2. **Polarization of Waves**: Polarization refers to the orientation of the electric field vector of an electromagnetic wave. The direction of polarization can affect how the wave interacts with the environment.

3. **Direction of Electric and Magnetic Fields**: In an electromagnetic wave, the electric field (E) and magnetic field (B) are perpendicular to each other and to the direction of wave propagation.

4. **Analyzing the Ground Wave Propagation**: For ground waves, the propagation occurs close to the Earth's surface. If we denote the direction of wave propagation as horizontal (parallel to the Earth's surface), we need to determine the orientation of the electric field.

5. **Determining Polarization**:
- If the ground wave is propagating horizontally, the electric field must be oriented vertically to maintain the perpendicular relationship between the electric and magnetic fields.
- This means the electric field is normal (perpendicular) to the Earth's surface.

6. **Conclusion**: Based on the analysis, the ground waves are polarized in a direction that is normal to the Earth's surface. Thus, the correct answer to the question is option B: Normal to Earth's surface.

### Final Answer:
Ground waves are polarized **normal to the Earth's surface**.

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