Total internal reflection and optical fibers

Equipment

• Two-media interface with incident, reflected and refracted rays
• Slider “Góc tới” (incidence angle)
• Sliders “Chiết suất n₁” and “Chiết suất n₂” (indices)
• “Đặt lại tham số” (reset) button

Procedure

1. Increase the incidence angle

   With n₁>n₂, drag the incidence-angle slider up slowly. The refracted ray bends away from the normal and runs along the interface at the critical angle; beyond $\theta_c$ no refracted ray exists and all light reflects. Read $\theta_c$ where the refracted ray vanishes.

2. Verify Snell's law

   Compute $\theta_c=\arcsin(n_2/n_1)$ from the slider indices and compare with your reading — for glass into air ($n_1=1.5$, $n_2=1.0$) expect $\theta_c\approx41.8°$. Then set a subcritical angle and check $n_1\sin\theta_1=n_2\sin\theta_2$ against the drawn refracted ray.

3. Build a light guide

   Reduce n₂ or raise n₁ so $\theta_c$ shrinks, then choose an incidence angle well above it — as in a fiber core at steep angles. Explain why rays bouncing along a fiber lose almost no energy, and what breaks the condition if the light arrives from air into glass.

Simulation

Experiment history

Related physicists

Related library topics