physics wave

Yuki

2013-12-16 6:40 am

1. Ans: D why is it not A?
圖片參考：http://imgcld.yimg.com/8/n/HA00274964/o/20131215223731.jpg
2. (6ei) ans: L1>L2
but I dun agree…the object is placed beyond 2F for L1 while it is placed withinF for L2... so L2 should have a larger focal length than L1?
圖片參考：http://imgcld.yimg.com/8/n/HA00274964/o/20131215223812.jpg
3. Ans: B
why is (3) incorrect?
圖片參考：http://imgcld.yimg.com/8/n/HA00274964/o/20131215223901.jpg
4. the amplitude of water particles on the nodal lines are smaller if two sources are used rather than one. does it disobey the law of conservation of energy? where does the energy go?

thanks!!

回答 (1)

天同

2013-12-16 7:59 pm

✔ 最佳答案

1. Option A should be the correct answer.

2. You are right that the focal length of L2 is longer than that of L1.

3. At t =0.05 s, the crest of the right-going wave and the trough of the left-going wave meet at C. After the waves pass over each other, the particle at mid-point of BC (call it B', say) will go downward, whereas particle at mid-point of CD (call it C', say) will go upward.
Thus, B' is actually moving in the downward direction, and C' is moving at the upward direction. They are not at rest (zero speed).

4. Interference is a process of re-distribution of wave energy. More energy goes to the antinodal lines and less energy goes to the nodal lines. There is no loss of energy.

2013-12-18 12:26:30 補充：
Your suppl question:
Particles along the nodal line are at rest if and only if the two waves producing the inteference pattern are of equal amplitudes.

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