Hi!!!
When we try to see a candle flame through a straight pipe , we can see it very clearly but, in the case of a bent pipe we cannot see it because light travels in a straight line and never bends. We are able to see because of light and it cannot pass through a Bent tube, as a result we cannot see the candle flame. This property of light of traveling in a straight line is known as The Rectilinear propagation of light. Thus, the candle flame cannot be seen through a bent tube as light doesn't bend.
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