When a ray of light enters a glass slab from air

Options

A. its wavelength decreases
B. its wavelength increases
C. its frequency increases
D. neither its wavelength nor its frequency changes

Answer

To solve the question regarding the behavior of a ray of light when it enters a glass slab from air, we can break it down into the following steps:

### Step 1: Understand the Medium Transition
When light travels from air (a rarer medium) into glass (a denser medium), it undergoes refraction. Refraction is the bending of light as it passes from one medium to another due to a change in its speed.

**Hint:** Remember that the speed of light is different in different media.

### Step 2: Analyze the Properties of Light
In any medium, the speed of light (v) is related to its frequency (ν) and wavelength (λ) by the equation:
\[ v = ν \times λ \]
When light enters a denser medium, its speed decreases.

**Hint:** Consider how the speed of light changes when it moves from a rarer to a denser medium.

### Step 3: Frequency Remains Constant
The frequency of light (ν) remains constant when it transitions between two media. This is because frequency is determined by the source of the light and does not change when light enters a different medium.

**Hint:** Think about the conservation of energy and how it relates to frequency.

### Step 4: Relationship Between Speed, Wavelength, and Frequency
Since the frequency remains constant and the speed of light decreases in the denser medium, we can deduce that the wavelength must also change. Using the relationship:
\[ λ = \frac{v}{ν} \]
If the speed (v) decreases while the frequency (ν) remains constant, the wavelength (λ) must also decrease.

**Hint:** Use the formula to see how changes in speed affect wavelength.

### Step 5: Conclusion on Wavelength Change
Thus, when light enters the glass slab from air, its wavelength decreases. The new wavelength (λ') in the glass can be expressed as:
\[ λ' = \frac{λ}{μ} \]
where μ is the refractive index of the glass.

**Hint:** Remember that the refractive index is a measure of how much the speed of light is reduced in a medium compared to vacuum.

### Final Answer
The correct option is that the wavelength decreases when a ray of light enters a glass slab from air.

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