A ray of light travels from a less dense medium to a denser medium. How are the speed and frequency of the light affected? The speed

Analyze the question: Light moves from a less dense (e.g. air) medium into a denser (e.g. glass or water) medium. We need to say what happens to its speed and its frequency.

Concept:

• Speed of light in a medium is v = c/n, where n is the refractive index. A denser medium has a higher n, so the speed decreases.
• Frequency is fixed by the source of the light. It does not change when light crosses a boundary, because the number of waves arriving at the boundary per second must equal the number leaving it per second. So the frequency remains the same.
• Since v = fλ and f is constant, a decrease in v means the wavelength λ also decreases. This is why light bends towards the normal when entering a denser medium.

Step-by-step solution:

1. Moving into a denser medium means n increases.
2. v = c/n, so v decreases.
3. The frequency is determined by the source, so f stays constant.
4. Wavelength decreases (λ = v/f).

Checking the options:

• A: Speed increases and frequency increases. Wrong on both.
• B: Speed decreases, which is right, but frequency does not decrease. Wrong.
• C: Speed does not increase. Wrong.
• D: Speed decreases and frequency remains the same. Correct.

Tip: When a wave crosses a boundary, remember "F is fixed". Speed and wavelength change together, but frequency never does. Going into a denser medium makes light slower, with a shorter wavelength and the same frequency.