*Question E3A04:
In what direction does an electromagnetic wave travel?*  

*Correct Answer is  D: It travels at a right angle to the electric and magnetic fields*  

### AI Response: (may contain errors)  

Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation. 

### Correct Answer: D
- **Why it's correct**: Electromagnetic waves travel at a right angle to both the electric field ($E$) and the magnetic field ($B$). This relationship can be visualized using the right-hand rule, where if you point your thumb in the direction of the wave's travel, your index finger points in the direction of the electric field, and your middle finger (perpendicular to the index) points in the direction of the magnetic field.

### Why the other choices are incorrect:
- **A: It depends on the phase angle of the magnetic field**  
  - This is incorrect because the direction of wave travel is not influenced by the phase angle of the magnetic field. The wave travels in a fixed direction determined by the orientation of the fields.

- **B: It travels parallel to the electric and magnetic fields**  
  - This is incorrect because the electric and magnetic fields are not in the same direction as the wave propagation. They are perpendicular to the direction of travel.

- **C: It depends on the phase angle of the electric field**  
  - This is also incorrect for the same reason as option A. The phase angle does not determine the direction of wave travel; it only affects the timing of the oscillations.

### Useful Rule of Thumb:
- Remember the right-hand rule for electromagnetic waves:  
  - Thumb: Direction of wave propagation  
  - Index Finger: Direction of the electric field  
  - Middle Finger: Direction of the magnetic field  

This understanding is crucial for grasping the behavior of electromagnetic waves in various applications, including radio communications.