## AngelicDragon 2 years ago We never learned this!!! I'll give a medal to whoever can help me!!! I've read and re-read my lessons like 7 times it's not there! The paths of the light waves that interfere to cause first-order lines A. differ in length by the wavelength of the light. B. are parallel lines. C. are the same length. D. differ in length by one-half of the wavelength of the light.

1. AngelicDragon

@Mashy Help Me!!! *Insert Anime crying* ='(

2. AngelicDragon

well anyone works but still

3. Mashy

you need to know what causes those bright and dark fringes in interference.. can you tell me why you get interference in the first place?

4. AngelicDragon

the interference occurs when waves either cancel each other out or reinforce each other

5. Mashy

and when do they reinforce each other? i mean what condition?

6. AngelicDragon

Two coherent waves traveling along two different paths to the same point will interfere destructively if there is a difference in distance traveled that is equivalent to a half number of wavelengths. And two coherent waves traveling along two different paths to the same point will interfere constructively if there is a difference in distance traveled that is equivalent to a whole number of wavelengths.

7. AngelicDragon

I that out of this site: http://www.physicsclassroom.com/Class/light/U12l3e.cfm (My lessons aren't that specific)

8. Mashy

there you go.. so now try to answer the questoin :P

9. AngelicDragon

So it would be A

10. Mashy

11. AngelicDragon

oh yeah. oops

12. Mashy

no .. answer me.. think !!

13. AngelicDragon

A little pushy aren't we? Okay. Fine. It COULD be C but if they were the same length then they would most likely cancel each other out. (I've learned for several years in a row that usually when something(s) are the same in measurement they tend to cancel each other out.)

14. AngelicDragon

So I still wanna stick with A even though I'm still considering C as a small possibility

15. AngelicDragon

Are you still there @Mashy ?

16. Shames

A. differ in length by the wavelength of the light.