phy 3 條mock mc 急
- 天同Lv 77 年 前最佳解答
19. The fringe separation should be 入v/z
I don't think any one of the options is correct.
20. There is no force acting on l2 as it is outside the magnetic field.
I suppose the magnetic field is pointing into the paper, the magnetc force on l3 is upward by using Fleming's Left Hand Rule (Motor Rule).
Since the magnetic force = NBIl
Hence, the net force = mg - NBIl
35. Since kinetic energy of recoil nucleus = E
E = (1/2).(N-4)V^2 where V is the recoil speed
V^2 = 2E/(N-4)
By conservation of momentum,
chnage of momentum of recoil nucleus = change of momentum of alpha
(N-4)V = 4v where v is the speed of the alpha particle
squaring on both sides,
(N-4)^2V^2 = 16v^2
v^2 = (N-4)^2V^2/16
v^2 = [(N-4)^2/16].[2E/(N-4)]
v^2 = (N-4)E/8
kinetic energy of alpha particle