Huygens explained the missing backwave by taking the amplitude zero:
ABackwards
BForwards
CSideways
DDownwards
Answer & Solution
Correct answer: A. Backwards
1. The construction would otherwise give a wave running backwards.
2. Huygens assumed the wavelets are strongest straight ahead.
3. He took their amplitude to be zero in the backward direction.
_Source: NCERT Class 12 Physics Part II, Chapter 10, Wave Optics._
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