Physics waves 一問

Q: trough + trough 係 maxima 定 minima??
A: It is maxima.
Constructive interference indicates two waves exactly overlapping each other. That is, a crest overlaps a crest and a trough overlaps with a trough. In fact, when the crests overlaps, the troughs will automatically overlapping as the wavelengths of the two waves are the same.

Destructive interference occurs when a crest overlaps with a trough.

Q: 點解係除3，唔係除1.5?
A: The (120.8cm) maximum is 3 orders higher than the (26.3 cm) maximum. This is how the 3 comes in. In other words, if the order of the (26.3cm) max is m, then the order of the (120.8cm) max is (m+3).

Q: 如果maxima = constructive interference 既話, 一個wavelength裡唔係應該有2個maxima咩?
A: No, you cannot say that. It is completely a wrong concept.
By maximum or minimum, we refer to the intensity maximum or minumun. That is, a bright or dark fringe. You cannot isolate a wave. Be aware that at the point of maximium intensity, the wave is actually continuously passing through the point. Do not construe that a crest or trough is stationary at that point.

Q: 點解係(1)(lamda), 唔係(0.5)(lamda)?
A: In general, it should be (lamds)/2 for destructive interference to occur. As I do not have the complete question, I don't know whether there is other factors involved that might shift the interference pattern by half a wavelength.

樓主放心 concept無錯 trough+trough的確係constructive interference樓主ge錯係錯係唔理解條題目je

05果條係microphone A同microphone B收到ge wave ge interference
假設係依刻microphone A收到ge wave係crest
microphone B要一樣收到crest先會做到constructive interference
所以mark低左ge position係 係果刻microphone B收到ge signal同為crest ge地方
兩個crest之間ge距離咪即係一個wavelengh lor~

08果條係問緊'IN the first-order spectrum'
即係佢問緊係依個spectrum入面intensity最弱ge light ge wavelengh幾多
原本如果就咁用white light射去個diffraction grating ge話
係angular position 33度出現ge光應該係green light
咁但係而家係果個位係minimum intensity
原因係thin film個path difference令green light做左destructive interference
所以intensity就係最弱
所以樓主只要當佢係問緊係angular position 33度出現ge光ge wavelengh係幾多咁計就得ga la