A Sound wave travels from air to water. The angle of incidence is \(\alpha_{1}\) and the angle of reflection is \(\alpha_{2}\) If the snell's Law is valid then, (A) \(\alpha_{1} \geq \alpha_{2}\) (B) \(\alpha_{1}=\alpha_{2}\) (C) \(\alpha_{1}>\alpha_{2}\) (D) \(\alpha_{1}<\alpha_{2}\)

Short Answer

Expert verified
(C) \(\alpha_{1} > \alpha_{2}\)

Step by step solution

01

Write down Snell's Law formula

Recall that Snell's Law states the relationship between the angles of incidence, refraction, and the refractive indices of the two mediums. The formula for Snell's Law is: \[ n_1 \sin\alpha_{1} = n_2 \sin\alpha_{2} \]
02

Relate the refractive indices to the speed of sound in each medium

Refractive index is the ratio of the speed of light in a vacuum to the speed of light in a given medium. For sound waves, we can use a similar ratio by defining the index of refraction as the ratio of the speed of sound in the reference medium (air) to the speed of sound in the given medium. Using this definition, we can write the refractive indices of air and water as \(n_1 = \frac{v_{air}}{v_{air}}\) and \(n_2 = \frac{v_{air}}{v_{water}}\), where \(v_{air}\) and \(v_{water}\) are the speeds of sound in air and water, respectively.
03

Insert the refractive indices into Snell's Law formula

Now, substitute the expressions for refractive indices into Snell's Law formula: \[ \frac{v_{air}}{v_{air}} \sin\alpha_{1} = \frac{v_{air}}{v_{water}} \sin\alpha_{2} \]
04

Simplify the equation

Notice that \(v_{air}\) cancels out on both sides of the equation, leaving: \[ \sin\alpha_{1} = \frac{v_{water}}{v_{air}} \sin\alpha_{2} \]
05

Compare the speeds of sound in air and water

In general, the speed of sound is faster in water than in air (\(v_{water} > v_{air}\)). Therefore, the fraction \(\frac{v_{water}}{v_{air}}\) is greater than 1.
06

Analyze the relationship between angles of incidence and refraction

With the information from the previous step, we can rewrite the equation as: \[ \sin\alpha_{1} = k \sin\alpha_{2}\ ,\quad k > 1 \] Since \(k\) is greater than 1, for the same values of \(\alpha_{1}\) and \(\alpha_{2}\), the sine of the angle of incidence will always be greater than the sine of the angle of refraction.
07

Determine the correct answer choice

Based on our analysis in Steps 5 and 6, we can conclude that when a sound wave travels from air to water, the angle of incidence \(\alpha_{1}\) will always be greater than the angle of refraction \(\alpha_{2}\). Therefore, among the given answer choices, the correct one is: (C) \(\alpha_{1} > \alpha_{2}\)

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