If the incident angle is less than the the critical angle, then you will have total internal reflection.
True
False
The correct answer and explanation is:
Correct Answer: ❌ False
Explanation (300 words):
The statement “If the incident angle is less than the critical angle, then you will have total internal reflection” is false.
Total internal reflection (TIR) occurs only when two conditions are met:
- Light travels from a medium with a higher refractive index to one with a lower refractive index (e.g., from water to air or glass to air).
- The angle of incidence is greater than or equal to the critical angle.
The critical angle is the minimum angle of incidence at which light, moving from a denser (higher refractive index) to a rarer (lower refractive index) medium, is completely reflected back into the denser medium rather than refracted out.
If the **incident angle is *less* than the critical angle**, light will *partially refract* into the second medium and partially reflect back into the first. Only when the angle of incidence equals or exceeds the critical angle does total internal reflection occur — meaning no refraction, just reflection.
Example:
- Suppose light travels from water (n ≈ 1.33) into air (n ≈ 1.00).
- The critical angle can be calculated using Snell’s Law: $$
\theta_c = \sin^{-1} \left( \frac{n_2}{n_1} \right) = \sin^{-1} \left( \frac{1.00}{1.33} \right) \approx 48.75^\circ
$$ - If the incident angle is:
- 30° (less than the critical angle): Light partially refracts into the air.
- 50° (greater than the critical angle): Total internal reflection occurs.
Thus, TIR does not happen if the incident angle is less than the critical angle, making the original statement false.