The fundamental source of e.m. waves

Options

A. is varying magnetic field
B. constant magnetic and electric fields
C. are continous oscillations of electric charge
D. is planets

Answer

### Step-by-Step Solution:

1. **Understanding Electromagnetic Waves (EM Waves)**:
- Electromagnetic waves (EM waves) are transverse waves that consist of oscillating electric and magnetic fields. They can propagate through a vacuum, meaning they do not require a medium to travel.

2. **Identifying the Fundamental Source**:
- We need to determine the fundamental source of EM waves from the given options:
1. Varying magnetic field
2. Constant magnetic and electric field
3. Continuous oscillations of electric charge
4. Planets

3. **Analyzing Each Option**:
- **Option 1: Varying Magnetic Field**:
- While a varying magnetic field can contribute to the generation of EM waves, it is not the fundamental source by itself, as it requires an oscillating electric field.

- **Option 2: Constant Magnetic and Electric Field**:
- A constant field does not lead to the generation of EM waves. EM waves are produced by changing fields, not constant ones.

- **Option 3: Continuous Oscillations of Electric Charge**:
- This is the correct option. When an electric charge oscillates, it creates a changing electric field, which in turn generates a magnetic field. The continuous oscillation of electric charge leads to the creation of both electric and magnetic fields that propagate as EM waves.

- **Option 4: Planets**:
- Planets themselves do not generate EM waves in the context of electromagnetic radiation. They may reflect or absorb EM waves but are not a source of them.

4. **Conclusion**:
- The fundamental source of electromagnetic waves is the continuous oscillations of electric charge (Option 3).

### Final Answer:
The fundamental source of electromagnetic waves is **continuous oscillations of electric charge**.

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