sarmita
Posts: 2
Joined: Sun Sep 11, 2005 3:48 am

pl. give some explanations for the following GRE question. Or if it is possible, pl. derive the solution:)

GR8677:Q3. For blue light, a transparent material has a relative permittivity (dielectric constant) of 2.1 and a relative permeability of 1.0. If the speed of light in a vacuum is c, the phase velocity of blue light in an unbounded medium of this material is

thermalEquilibrium
Posts: 12
Joined: Thu Sep 15, 2005 2:37 pm
Hey ,

use the fact that the speed of light in a medium is c=1/(e u)^0.5

where e, and u are epsilon and mu

for a vacuum i will use e_o and u_o

for this dielectric e=2.1 e_o , u=u_o

c=1/(2.1e_o u_o)^0.5, but c_o=1/(e_o u_o)

therefore c=c* 1/(2.1)^0.5

i think there is a slight mistake in how the problem is presented. The wording of
For blue light, a transparent material has a relative permittivity (dielectric constant) of 2.1 and a relative permeability of 1.0.
doesnt quite make sense.... i assume they mean that the dielectric constant outside the material is 1.0

sarmita
Posts: 2
Joined: Sun Sep 11, 2005 3:48 am

### thanks for the reply

hi
Thanks for the reply.

i think the problem is ok. As we know that sometimes the relative permittivity is called the dielectric constant of the material.

U have done a good job. ur approach is perfectly o.k.

actually my problem is i am out of touch of physics more than 5years. i am starting from the base, as u can say from undergraduate level. i have forgotten many things. if u kindly give inputs like this it would be of great pleasure for me.

thanks again.

yosofun
Posts: 87
Joined: Mon Oct 31, 2005 5:50 am
the solution posted here is very detailed and may help you:
http://grephysics.yosunism.com/disp.php ... l=1&prob=3