In frequency modulation

Options

A. the amplitude of modulated wave varies as frequency of carrier wave
B. the frequency of modulated wave varies as amplitude of modulating wave
C. the amplitude of modulated wave varies as amplitude of carrier wave
D. the frequency of modulated wave varies as frequency of modulating wave

Explanation

To solve the question regarding frequency modulation, we need to analyze the options provided and determine which statement correctly describes the relationship in frequency modulation. Here’s a step-by-step solution:

### Step 1: Understand Frequency Modulation
Frequency modulation (FM) is a technique used to encode information in a carrier wave by varying its frequency. In FM, the amplitude of the carrier wave remains constant while its frequency changes according to the amplitude of the modulating signal.

### Step 2: Analyze Each Option
1. **Option 1**: "The amplitude of modulated wave varies as frequency of carrier wave."
- This is incorrect because in frequency modulation, the amplitude of the carrier wave does not vary; only the frequency changes.

2. **Option 2**: "The frequency of modulated wave varies as amplitude of modulated wave."
- This is also incorrect. In frequency modulation, it is the frequency of the carrier wave that varies with the amplitude of the modulating signal, not the frequency of the modulated wave with respect to its amplitude.

3. **Option 3**: "Amplitude of modulated wave varies as amplitude of carrier wave."
- This statement is incorrect as well. The amplitude of the modulated wave in frequency modulation does not change; it remains constant.

4. **Option 4**: "The frequency of modulated wave varies as frequency of modulating wave."
- This statement is correct. In frequency modulation, the frequency of the carrier wave is varied in accordance with the frequency of the modulating signal.

### Step 3: Conclusion
The correct answer is **Option 4**: "The frequency of modulated wave varies as frequency of modulating wave." This accurately describes the principle of frequency modulation.