When a ray of light enters a transparent medium, what changes does it undergo?

Appeared in: HSSC Staff Nurse - 2015

Explanation

When light enters a new transparent medium, its velocity changes because the optical density (refractive index) of the new medium is different.
The frequency of the light wave is determined by its source and remains constant regardless of the medium it travels through.
According to the wave equation (velocity = frequency × wavelength), since velocity changes and frequency remains constant, the wavelength must also change.
Therefore, both the wavelength and the velocity of the light ray undergo a change.

Option A: This is incorrect because the frequency of a light wave is determined by its source and remains constant when it enters a new medium.
Option B: This is incomplete. While the wavelength does change, the velocity of the light also changes as it enters a medium with a different refractive index.
Option D: This is incorrect because the frequency of the light wave remains constant. Only the velocity and wavelength change.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Refraction of light and properties of waves as background academic context rather than a clinical decision trigger.
The principle of refraction is fundamental to vision. The cornea and lens of the human eye refract (bend) light to focus it onto the retina, allowing us to see clearly.
This concept is the basis for corrective lenses. Eyeglasses and contact lenses correct refractive errors like myopia (nearsightedness) and hyperopia (farsightedness) by altering the path of light before it enters the eye.
Medical instruments like endoscopes and ophthalmoscopes rely on the principles of optics, including refraction and reflection, to visualize internal body structures.

How to Approach the Question

First, identify that the question is about the fundamental properties of a wave (light) as it changes medium.
Recall the most important rule for waves changing media: frequency is determined by the source and remains constant.
This key rule immediately eliminates any option that includes a change in frequency (in this case, 'Frequency only' and 'Velocity and Frequency both').
Next, consider the velocity. The speed of light depends on the optical density (refractive index) of the medium. Since the medium is changing, the velocity must also change.
Finally, use the wave equation: velocity = frequency × wavelength. Since you know velocity changes and frequency is constant, it logically follows that the wavelength must also change.
This leads to the conclusion that both wavelength and velocity change.

Concept Tested & Keywords

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E6 Physiology Guyton 4SAE Part 3 p. 137-139

Practise the full HSSC Staff Nurse - 2015

Attempt every question from this paper in a timed mock, then review the full solution for each one.