Is Snell's law applicable when a ray of light is incident perpendicular to the normal at the point of incidence?

Options

A. Yes
B. No
C. data is not given
D. It is an exception for the validity of the law.

Explanation

To determine whether Snell's law is applicable when a ray of light is incident perpendicular to the normal at the point of incidence, we can follow these steps:

### Step 1: Understand Snell's Law
Snell's law relates the angles of incidence and refraction for light passing through different media. It is mathematically expressed as:
\[ n_1 \sin r_1 = n_2 \sin r_2 \]
where:
- \( n_1 \) and \( n_2 \) are the refractive indices of the two media,
- \( r_1 \) is the angle of incidence,
- \( r_2 \) is the angle of refraction.

### Step 2: Analyze the Situation
When a ray of light is incident perpendicular to the normal, the angle of incidence \( r_1 \) is 0 degrees. In this case, the sine of 0 degrees is:
\[ \sin(0) = 0 \]

### Step 3: Apply Snell's Law
Substituting \( r_1 = 0 \) into Snell's law gives:
\[ n_1 \sin(0) = n_2 \sin(r_2) \]
This simplifies to:
\[ 0 = n_2 \sin(r_2) \]
This equation implies that \( \sin(r_2) \) must also be 0, which means that \( r_2 \) is also 0 degrees. Therefore, the light ray continues in the same direction without any deviation.

### Step 4: Conclusion
Since the light ray does not deviate when it is incident perpendicular to the normal, Snell's law does not apply in the conventional sense, as it is based on the assumption of deviation. Thus, the situation where the ray is incident perpendicular to the normal is an exception to the validity of Snell's law.

### Final Answer
Yes, Snell's law is not applicable when a ray of light is incident perpendicular to the normal at the point of incidence; it is an exception for the validity of the law.

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