A shortcoming of Huygen's model could not

Options

A. explaining the absence of the backwave
B. determine the shape of the wavefront for a plane wave
C. explain the point source emitting waves uniformly in all directions
D. All of the above

Explanation

To address the question regarding the shortcomings of Huygens' model, we will analyze the key points and provide a structured solution.

### Step-by-Step Solution

1. **Understanding Huygens' Principle**:
Huygens' principle states that every point on a wavefront can be considered a source of secondary wavelets. The new wavefront is formed by the envelope of these wavelets.

2. **Identifying the Shortcomings**:
One major shortcoming of Huygens' model is its inability to explain the absence of back waves. Huygens assumed that when a wavefront propagates, it only moves forward and does not produce any waves behind it.

3. **Explaining the Absence of Back Waves**:
In reality, when a wavefront travels, the particles at the back of the wavefront are still oscillating. This means that while there are secondary wavelets produced at the back, their effects cancel each other out due to destructive interference. Therefore, there is no net effect of a back wave.

4. **Conclusion**:
Huygens' model fails to account for the oscillations of particles at the back of the wavefront, leading to the conclusion that it cannot explain the absence of back waves.

### Final Answer:
The shortcoming of Huygens' model is that it could not explain the absence of back waves, as it assumed that no waves are produced behind the propagating wavefront.

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