The presence of dangerous gases in mines can be detected using the phenomenon of

Options

A. echo
B. doppler effect
C. beats
D. resonance

Answer

To solve the question about detecting dangerous gases in mines, we need to identify the phenomenon that allows us to differentiate between gases based on sound properties. Here’s a step-by-step solution:

### Step 1: Understand the Question
The question asks about a phenomenon used to detect the presence of dangerous gases in mines. We need to analyze the options provided: echo, Doppler effect, beats, and resonance.

**Hint:** Identify what each phenomenon entails and how it relates to sound and gases.

### Step 2: Analyze the Options
1. **Echo**: This is the reflection of sound waves. While it can help in determining distances, it does not help in identifying gas types.

2. **Doppler Effect**: This phenomenon involves the change in frequency of a wave in relation to an observer moving relative to the source of the wave. It is not specifically used for gas detection.

3. **Beats**: This phenomenon occurs when two sound waves of slightly different frequencies interfere with each other, creating a pattern of sound that fluctuates in volume. This can be used to detect differences in the speed of sound in different gases.

4. **Resonance**: This is the amplification of sound when the frequency of a force matches the natural frequency of a system. It does not directly relate to gas detection.

**Hint:** Focus on how sound behaves differently in various gases and which option relates to that behavior.

### Step 3: Identify the Correct Phenomenon
The correct answer is **beats**. When sound travels through different gases, it travels at different speeds, leading to different frequencies. If two sound sources (one from a normal air environment and another from a gas-filled environment) are compared, they will produce beats if their frequencies differ. This indicates the presence of different gases.

**Hint:** Remember that beats are a result of interference between two sound waves, which can indicate differences in the medium they travel through.

### Step 4: Conclusion
Thus, the presence of dangerous gases in mines can be detected using the phenomenon of **beats**. This method relies on the fact that the speed of sound varies with the type of gas present, leading to distinguishable frequencies when compared.

**Final Answer:** The presence of dangerous gases in mines can be detected using the phenomenon of **beats**.

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