Please help~~
2011-03-05 8:26 pm
圖片參考：http://imgcld.yimg.com/8/n/HA00370005/o/701103050048413873386870.jpg
12. The following figure shows an apparatus for measuring the speed of light c. Light is incident at P on one face of an octagonal mirror M and then traverses a path PQRS, of total length L, before being reflected again from another face of M.
14. Two identical narrow slits S1 and S2 are illuminated by light of wavelength from a point source P.If, as shown in the figure above, the light is then allowed to fall on a screen, and if m is a positive integer, the condition for destructive interference at Q is that
A. l3- l4 = (2m+1)入/2
B. l3- l4 = m入
C. (l1+ l3) - (l2 + l4) = (2m+1) = 入/2
D. (l1+ l3) - (l2 + l4) = (2m+1) = m入
19. The figure shows an object O placed at the focus of a converging lens L. A concave mirror M is arranged on the other side of L and is 80 cm from it. If the focal length of L is 60 cm and the final image formed by this system is at infinity, what is the focal length of M?A. 20 cmB. 30 cmC. 40 cmD. 70 cm30. An aluminium ring hangs vertically from a thread with its axis pointing east-west. A coil is fixed near to the ring and coaxial with it.
回答 (2)
2011-03-05 9:31 pm
✔ 最佳答案
12. Your question is incomplete.14. Option AFor constructive interference, the two paths should have a difference of half of a wavelength, i.e. [(m+1/2).wavelength]
19. Because the object is placed at one of the foci of the lens, light rays after passing through the lens, are parallel. The parallel light rayw will then incident onto the concave mirror M. After reflection by M, the light rays wll converge at the focus of M (say, f').
If f' coincides with the focus of the lens, then light rays will be refracted parallel by the lens, forimg image at infinity.
Thus, it is clear that f + f' = 80where f is the focal length of the lens, and f' the focal length of the concave mirrori.e. f' = (80 -60) cm = 20 cmThe answer is option A
30 Your question is imcomplete.
2011-03-05 11:47 pm
12. M is rotated about its axis of symmetry as indicated and its angular velocity is adjusted until the light emerges in the same direction as when M is stationary. What is the smallest angular velocity at which this condition is achieved?
A. pi c/ 8L B. pi c/4L c. pi c/2L D. pi c/L
2011-03-05 15:48:12 補充：
30. What is the initial motion of the aluminium ring when the current in the coil is switched on?
A. remains at rest B. moves towards S
C. moves towards W D. moves towards E
A. pi c/ 8L B. pi c/4L c. pi c/2L D. pi c/L
2011-03-05 15:48:12 補充：
30. What is the initial motion of the aluminium ring when the current in the coil is switched on?
A. remains at rest B. moves towards S
C. moves towards W D. moves towards E
收錄日期: 2021-04-29 17:45:30
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20110305000051KK00484