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CGP EDU Academic Team
Published on: September 12, 2026
The critical angles for total internal reflection is ......... when a ray of light travels from glass to water than when it travels from glass to air.
Text Solution
Verified by ExpertsThe correct answer is:
B
Step 1: Understand the concept of critical angle. The critical angle is defined as the angle of incidence above which total internal reflection occurs. It depends on the index of refraction of the two media involved.
Step 2: The formula for critical angle ($C$) is given by Snell's Law as follows:
$$C = ext{sin}^{-1} \left( \frac{n_2}{n_1} \right)$$ where
- $n_1$ is the refractive index of the medium from which the light is coming (glass in this case)
- $n_2$ is the refractive index of the second medium (water or air).
Step 3: For glass to air, typically, the refractive index of glass is around 1.5 and air is approximately 1. Thus, the critical angle when light moves from glass to air is:
$$C_{glass-air} = \text{sin}^{-1} \left( \frac{1}{1.5} \right)$$
Step 4: For glass to water, the refractive index of water is about 1.33. Thus, the critical angle when light moves from glass to water is:
$$C_{glass-water} = \text{sin}^{-1} \left( \frac{1.33}{1.5} \right)$$
Step 5: Comparing the two critical angles calculated, we find that the critical angle for glass to air is greater than that for glass to water:
Thus, the statement in the question indicates that the critical angle for total internal reflection is less when a ray of light travels from glass to water than from glass to air.
Therefore, the correct answer is Option B.
Step 2: The formula for critical angle ($C$) is given by Snell's Law as follows:
$$C = ext{sin}^{-1} \left( \frac{n_2}{n_1} \right)$$ where
- $n_1$ is the refractive index of the medium from which the light is coming (glass in this case)
- $n_2$ is the refractive index of the second medium (water or air).
Step 3: For glass to air, typically, the refractive index of glass is around 1.5 and air is approximately 1. Thus, the critical angle when light moves from glass to air is:
$$C_{glass-air} = \text{sin}^{-1} \left( \frac{1}{1.5} \right)$$
Step 4: For glass to water, the refractive index of water is about 1.33. Thus, the critical angle when light moves from glass to water is:
$$C_{glass-water} = \text{sin}^{-1} \left( \frac{1.33}{1.5} \right)$$
Step 5: Comparing the two critical angles calculated, we find that the critical angle for glass to air is greater than that for glass to water:
Thus, the statement in the question indicates that the critical angle for total internal reflection is less when a ray of light travels from glass to water than from glass to air.
Therefore, the correct answer is Option B.
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