For transmission of e.m.wave of audible frequency, these waves are superimposed with waves of

Options

A. frequency less than 20 Hz
B. frequency less than 10 KHz.
C. frequency in the audible range.
D. radio-frequency.

Explanation

To solve the question, "For transmission of e.m. wave of audible frequency, these waves are superimposed with waves of," we need to analyze the options given and understand the concept of modulation in communication systems.

### Step-by-Step Solution:

1. **Understanding Audible Frequencies**:
- Audible frequencies are those that can be heard by the human ear, typically ranging from 20 Hz to 20 kHz.

2. **Challenges with Low Frequencies**:
- Transmitting signals at low frequencies (like those in the audible range) can lead to several issues:
- **Attenuation**: Loss of signal strength over distance.
- **Noise Addition**: Increased interference from environmental noise.
- **Antenna Size**: Larger antennas are required for lower frequencies, which is impractical.

3. **Need for Higher Frequency**:
- To overcome these challenges, we use modulation, where the audible frequency signal is superimposed onto a higher frequency carrier wave. This allows for better transmission characteristics.

4. **Choosing the Right Frequency**:
- The carrier wave must be of a frequency that is significantly higher than the audible range to effectively carry the information without distortion.
- Frequencies below 20 Hz (infrasound) and below 10 kHz would not be suitable as they do not provide the necessary advantages of higher frequencies.

5. **Conclusion**:
- The best option for superimposing with audible frequencies is to use **radio frequency** waves, which are typically in the range of megahertz (MHz) to gigahertz (GHz). This ensures efficient transmission with minimal loss and noise.

### Final Answer:
For transmission of e.m. wave of audible frequency, these waves are superimposed with waves of **radio frequency**.

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