A ray of light travels obliquely from a less dense medium to a denser medium. Which of the following statements is true about the light?

Step 1: Analyze the question Light moves at an angle (obliquely) from a less dense (optically rarer) medium, such as air, into a denser medium, such as glass or water. We need to find the true statement about what happens to the light.

Step 2: The concept When light enters a different medium, its speed changes, and this causes refraction. The key relationships are:

• Frequency (f) is set by the source and does not change when light crosses a boundary.
• Speed: v = c/n, so in a denser medium (higher refractive index n), the speed decreases.
• Wavelength: v = fλ. Since f is constant and v decreases, λ decreases.
• Direction: by Snell's law, n₁ sin i = n₂ sin r. Going from low n to high n gives sin r < sin i, so r < i. The ray bends towards the normal.

Step 3: Check each option

• A. Wavelength increases: False. Speed drops and frequency stays the same, so the wavelength decreases.
• B. Speed increases: False. Light slows down in a denser medium.
• C. Light refracts towards the normal: True. The angle of refraction is smaller than the angle of incidence.
• D. Frequency changes: False. Frequency stays constant across the boundary.

Step 4: Answer The correct option is C.

Exam tip: Remember "Frequency is Fixed". Also remember "Slow = Squeeze toward the normal": going into a denser medium, light slows down, its wavelength shortens, and it bends toward the normal. Going into a less dense medium, it bends away from the normal.