jkang wrote:A wave has a phase velocity of 2c (where c = the speed of light in a vacuum). How is this possible?
I have two possible explanations: 1. The wave has entered a theoretical material with a refractive index of 0.5. 2. The wave manages to have an incredibly short period.
If neither of those is true then I'm clueless.
Sorry, neither are correct. As a hint, phase is the key word here.
Re: Optics B/C
Posted: March 13th, 2017, 10:22 am
by Adi1008
jkang wrote:
Avogadro wrote:
jkang wrote:A wave has a phase velocity of 2c (where c = the speed of light in a vacuum). How is this possible?
I have two possible explanations: 1. The wave has entered a theoretical material with a refractive index of 0.5. 2. The wave manages to have an incredibly short period.
If neither of those is true then I'm clueless.
Sorry, neither are correct. As a hint, phase is the key word here.
The Theory of Relativity says that information cannot travel faster than the speed of light. The refractive index is a measure of the phase velocity of light, which does not carry information, so it is able to be less than 1.
Re: Optics B/C
Posted: March 13th, 2017, 1:07 pm
by jkang
Adi1008 wrote:
jkang wrote:
Avogadro wrote:
I have two possible explanations: 1. The wave has entered a theoretical material with a refractive index of 0.5. 2. The wave manages to have an incredibly short period.
If neither of those is true then I'm clueless.
Sorry, neither are correct. As a hint, phase is the key word here.
The Theory of Relativity says that information cannot travel faster than the speed of light. The refractive index is a measure of the phase velocity of light, which does not carry information, so it is able to be less than 1.
This is correct. Because phase velocity doesn't contain information, it has the ability to travel faster than c. The Wikipedia for refractive index has your answer almost word for word. Your turn!
Re: Optics B/C
Posted: March 15th, 2017, 2:12 pm
by Adi1008
jkang wrote:
Adi1008 wrote:
jkang wrote:
Sorry, neither are correct. As a hint, phase is the key word here.
The Theory of Relativity says that information cannot travel faster than the speed of light. The refractive index is a measure of the phase velocity of light, which does not carry information, so it is able to be less than 1.
This is correct. Because phase velocity doesn't contain information, it has the ability to travel faster than c. The Wikipedia for refractive index has your answer almost word for word. Your turn!
What is the smallest time delay required between two waves of 400nm light to obtain complete destructive interference?
Re: Optics B/C
Posted: March 15th, 2017, 3:33 pm
by Tom_MS
Adi1008 wrote: What is the smallest time delay required between two waves of 400nm light to obtain complete destructive interference?
You can answer I just wanted to give it a shot.
6.67*10^-16 seconds. This is using the distance over time definition of the speed of light with a 200nm distance to create fully destructive interference.
Re: Optics B/C
Posted: March 15th, 2017, 3:36 pm
by Adi1008
Tom_MS wrote:
Adi1008 wrote: What is the smallest time delay required between two waves of 400nm light to obtain complete destructive interference?
You can answer I just wanted to give it a shot.
6.67*10^-16 seconds. This is using the distance over time definition of the speed of light with a 200nm distance to create fully destructive interference.
That's correct; your turn!
Re: Optics B/C
Posted: March 17th, 2017, 8:20 am
by Tom_MS
Adi1008 wrote:That's correct; your turn!
A certain lens has an index of refraction of 1.5, a front lens radius of 0.09 m, and a back surface lens of -0.04 m according to the cartesian sign convention. If it is 0.10 m thick, determine the front vertex power.
Re: Optics B/C
Posted: March 19th, 2017, 11:07 am
by Sean_Sylvester1
Tom_MS wrote:
Adi1008 wrote:That's correct; your turn!
A certain lens has an index of refraction of 1.5, a front lens radius of 0.09 m, and a back surface lens of -0.04 m according to the cartesian sign convention. If it is 0.10 m thick, determine the front vertex power.
Using the lensmakers formula and its derivation for thick lenses, I came up with an answer of 13.42 diopters
Re: Optics B/C
Posted: March 19th, 2017, 2:54 pm
by Tom_MS
Sean_Sylvester1 wrote:
Tom_MS wrote:
Adi1008 wrote:That's correct; your turn!
A certain lens has an index of refraction of 1.5, a front lens radius of 0.09 m, and a back surface lens of -0.04 m according to the cartesian sign convention. If it is 0.10 m thick, determine the front vertex power.
Using the lensmakers formula and its derivation for thick lenses, I came up with an answer of 13.42 diopters
Almost. To find the front vertex power you need to subtract the equivalent focal length by the distance from the front of the lens to the first principal plane.
Re: Optics B/C
Posted: March 19th, 2017, 4:38 pm
by Sean_Sylvester1
Tom_MS wrote:
Sean_Sylvester1 wrote:
Tom_MS wrote:
A certain lens has an index of refraction of 1.5, a front lens radius of 0.09 m, and a back surface lens of -0.04 m according to the cartesian sign convention. If it is 0.10 m thick, determine the front vertex power.
Using the lensmakers formula and its derivation for thick lenses, I came up with an answer of 13.42 diopters
Almost. To find the front vertex power you need to subtract the equivalent focal length by the distance from the front of the lens to the first principal plane.
Is it 64 diopters then? Since the equivalent focal length is the inverse of power and then subtract .09 from that