When unpolarised light beam is incident from air onto glass (`n=1.5`) at the polarising angle

Options

A. reflected beam is polarised 100 percent
B. reflected and refracted beams are partially polarised
C. the reason for (a) is that almost all the light is reflected
D. All of the above

Explanation

To solve the problem, we need to analyze the behavior of unpolarized light when it strikes a glass surface at the polarizing angle, also known as Brewster's angle. Here’s a step-by-step solution:

### Step 1: Understand Brewster's Law
Brewster's Law states that when unpolarized light hits a surface at a specific angle (the Brewster angle), the reflected light is completely polarized. The Brewster angle (θ_B) can be calculated using the formula:
\[ \tan(\theta_B) = \frac{n_2}{n_1} \]
where \( n_1 \) is the refractive index of the first medium (air, which is approximately 1) and \( n_2 \) is the refractive index of the second medium (glass, which is given as 1.5).

### Step 2: Calculate Brewster's Angle
Using the values:
- \( n_1 = 1 \) (for air)
- \( n_2 = 1.5 \) (for glass)

We can calculate Brewster's angle:
\[ \tan(\theta_B) = \frac{1.5}{1} = 1.5 \]
Now, we find the angle:
\[ \theta_B = \tan^{-1}(1.5) \]
Calculating this gives:
\[ \theta_B \approx 56.31^\circ \]

### Step 3: Analyze the Reflected Light
According to Brewster's Law, when light is incident at Brewster's angle:
- The reflected light is completely polarized.
- The electric field vector of the reflected light is perpendicular to the plane of incidence.

### Step 4: Analyze the Refracted Light
The refracted light that passes into the glass is partially polarized. This means that while it retains some degree of polarization, it is not fully polarized like the reflected light.

### Step 5: Evaluate the Options
Now, we can evaluate the given options:
1. **Reflected beam is polarized 100%** - This is true as per Brewster's Law.
2. **Reflected and refracted beam are partially polarized** - This is false; only the refracted beam is partially polarized.
3. **Reason for B is that almost all light is reflected** - This is misleading; the reflected light is fully polarized, not just "almost all."
4. **All of the above** - This is incorrect as options 2 and 3 are not true.

### Conclusion
The correct answer is that the reflected beam is 100% polarized.

### Final Answer
The correct option is **A: Reflected beam is polarized 100%**.

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