Question

A light ray travels obliquely from a denser medium to a rarer medium. It will bend:

• A. Towards the normal
• B. Away from the normal
• C. Along the normal
• D. It will not bend

Hint:

Remember the memory acronyms:
- D to R: Denser to Rarer \(\to\) Away from normal (DRA).
- R to D: Rarer to Denser \(\to\) Towards normal (RDT).

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks about the direction of bending of a light ray when it crosses an interface obliquely, moving from an optically denser medium to an optically rarer medium.

Step 2: Key Formula or Approach:
According to Snell's Law of refraction:
\[ n_1 \sin \theta_1 = n_2 \sin \theta_2 \]
where:
\(n_1, n_2\) are the refractive indices of medium 1 and 2,
\(\theta_1\) is the angle of incidence,
\(\theta_2\) is the angle of refraction.

Step 3: Detailed Explanation:

• Let medium 1 be optically denser (higher refractive index, \(n_1\)) and medium 2 be optically rarer (lower refractive index, \(n_2\)). Therefore:
\[ n_1 \gt n_2 \]

• From Snell's Law:
\[ \frac{\sin \theta_2}{\sin \theta_1} = \frac{n_1}{n_2} \]

• Since \(n_1 \gt n_2\), it must be that:
\[ \sin \theta_2 \gt \sin \theta_1 \implies \theta_2 \gt \theta_1 \]

• The angle of refraction (\(\theta_2\)) is greater than the angle of incidence (\(\theta_1\)). This means the refracted ray travels at a larger angle relative to the normal line compared to the incident ray.

• This geometric change means the ray bends away from the normal as it speeds up in the rarer medium.


Step 4: Final Answer:
The light ray will bend away from the normal.