phy questions...plz come come

Xxx

2011-09-05 1:25 am

3 phy questions...plz explain the reason why this is the answer~~~ detail!!!
http://imageshack.us/g/717/31608121.png/

更新1:

再加:: http://imageshack.us/photo/my-images/577/98333957.png/

更新2:

第一題其實我唔明你講咩.. 條題目係想問咩???(唔使translate做中文...) 可唔可以晝出黎..? 我唔明點解無啦啦有個2.pi???1/8???咩黎

更新3:

可唔可以晝下第一題???(最好晝啦) 因為我唔太明點解wavelength 一時係8,一時係1/8...

更新4:

sorry~打錯..係一時4, 一時1/8

更新5:

我寄左另外一題的補充問題比你... 答案是b...我想知點解唔係a 因為那裡的位置有限,希望你能解答回答我的補充問題

更新6:

thanks very much!!!!thanks very much!!!!

更新7:

你還有2題問題未回答.. http://imageshack.us/photo/my-images/577/98333957.png/ and 另外一題私下sd左比你謝謝!!!

更新8:

SORRY~係仲有一題.. http://imageshack.us/photo/my-images/577/98333957.png/

更新9:

SORRY~原來只有一題未答~ http://imageshack.us/photo/my-images/577/98333957.png/

回答 (1)

天同

2011-09-05 3:25 am

✔ 最佳答案

1. Option B

wavelength = 8/2 m = 4 m
Distance between two crests along the wall = 4/sin(pi/6) m = 8 m
Hence, point 1 m apart along the wall = (1/8) wavelength = (2.pi)/8 radians = pi/4 radians

2. Option B

If you sketch out the resultant wave, the peak of the resultant first occurs at position of 1/8 period on the time axis.
Since the first peak of wave P occurs at 1/4 period along the time axis, the difference in time of the two waves = (1/4 - 1/8) period = 1/8 period, which corresponds to a phase difference of 360/8 degrees = 45 degrees

3. Option A

It is clear from the graphs of P and Q that the peak of P appears earlier in time than the peak of Q by 1/4 period, which corresponds to a phase difference of 2.pi/4 radians = pi/2 radians
.

2011-09-04 20:36:16 補充：
1. The question is to find the phase difference between 2 points 1 metre apart on the wall.

2011-09-04 20:39:14 補充：
Since 1 wavelength (which is 2.pi radians in phase angle) corresponds to a distance of 8 m apart along the wall, by simple proportion, distance of 1 m on the wall corresponds to (2.pi)/8 radians.

2011-09-04 22:49:10 補充：
The diagram is already given in the question.
SImply, the distance between 2 crests measured ALONG THE WALL is 8m. But this corresponds to 1 wavelength, and 1 wavelength corresponds to phase angle of 2.pi radian (pi = 3.14159...)

2011-09-04 22:51:57 補充：
(cont'd)... hence, the phase angle between 2 points 1 m apart ALONG THE WALL, by proportion, = (1m/8m) x (2.pi) radians = (2.pi/8) radians = pi/4 radians.

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