ขอต้อนรับ ผู้มาเยือน กรุณา ล็อกอิน หรือ สมัครสมาชิก

ล็อกอินด้วยชื่อผู้ใช้ รหัสผ่่าน และระยะเวลาใช้งาน

 
Advanced search

41486 Posts in 6257 Topics- by 9141 Members - Latest Member: a duty
Pages: 1   Go Down
Print
Author Topic: GR8677.072  (Read 2574 times)
0 Members and 1 Guest are viewing this topic.
conantee
SuperHelper
*****
Offline Offline

Posts: 1400

เราเป็นอย่างไร สังคมเป็นอย่างนั้น


« on: January 06, 2010, 12:35:23 PM »

72. The measured index of refraction of x-rays in rock salt is less than one. This is consistent with the theory of relativity because
(A) relativity deals with light waves traveling in a vacuum only
(B) x-rays cannot transmit signals
(C) x-rays photons have imaginary mass
(D) the theory of relativity predates the development of solid-state physics
(E) the phase velocity and group velocity are different
Logged
conantee
SuperHelper
*****
Offline Offline

Posts: 1400

เราเป็นอย่างไร สังคมเป็นอย่างนั้น


« Reply #1 on: October 13, 2010, 08:34:39 AM »

You can do this by eliminating choices.
(B) is obviously wrong. x-ray can transmitted signals - like other photons (radio wave, visible light etc.)
(D) is also wrong. The theory of relativity can be applied to solid-state physics
(C) is wrong. This requires a bit of knowledge in relativity. Photons actually has zero rest mass - not imaginary mass.
(A) is wrong. Relativity applies to in other medium too, just like Newtonian mechanics or E&M. There are several questions in relativity class on light in material with n>1.

The correct answer is (E). The phase velocity is the velocity of phase. It can be greater than c since it does not represent the speed of physical object, while the group velocity does.

The correct answer is (E). 63 of 100 people answered this question correctly.
Logged
Pages: 1   Go Up
Print
Jump to: