(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

## n_1 = \sqrt{ \epsilon _1} ## .....(1) ,

## n_2 = 1 ## .....(2)

## \frac { \sin {\theta_i}}{ \sin {\theta_l} } = \frac { n_1}{n_2} = n_1 ## .....(3)

## \cos{\theta_1} = \frac { n_2}{n_1} = \frac1{ n_1} ## .....(4)

According to the question, the dielectric constant should be such that even when the incident angle is slightly less than ## \frac { \pi} 2 ## , the ray should come out of the rod without getting absorbed.

So, ## \theta _i \leq \frac { \pi} 2 ## .....(5)

Taking ##\theta _i = \frac { \pi} 2 ## , .....(6) I don't know why I am taking this.

## \frac1{ \sin {\theta_l} }= n_1 ## .....(7)

## \cos{\theta_1} = \frac1{ n_1} ## .....(8)

From (7) and (8), I get

## n_1 = \sqrt{ 2} ## .....(9)

From (1), ## \epsilon _1 = n_1^2 ## .....(10)

So, that dielectric constant = 2, option (c).

Is this correct?

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# Homework Help: Dielectric constant of a rod

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