Math Problem Statement

A 10 cm thick flat slab (n = 1.49) is placed in the air. A ray of light hits the front surface of the flat slab with an incident angle of 60 degrees. How much is the emergent ray displaced (d)?

Solution

To solve this problem, we need to calculate the lateral displacement (dd) of the emergent ray as it passes through the flat slab. Here's a step-by-step guide:

Step 1: Use Snell's Law to find the angle of refraction

Snell's Law relates the angle of incidence (θi)(\theta_i) to the angle of refraction (θr)(\theta_r): n1sin(θi)=n2sin(θr)n_1 \sin(\theta_i) = n_2 \sin(\theta_r) where:

  • n1=1n_1 = 1 is the refractive index of air,
  • n2=1.49n_2 = 1.49 is the refractive index of the slab,
  • θi=60\theta_i = 60^\circ is the angle of incidence.

We want to find θr\theta_r, the angle of refraction inside the slab: 1sin(60)=1.49sin(θr)1 \cdot \sin(60^\circ) = 1.49 \cdot \sin(\theta_r) sin(θr)=sin(60)1.49\sin(\theta_r) = \frac{\sin(60^\circ)}{1.49} sin(θr)=0.8661.490.581\sin(\theta_r) = \frac{0.866}{1.49} \approx 0.581 θrarcsin(0.581)35.55\theta_r \approx \arcsin(0.581) \approx 35.55^\circ

Step 2: Calculate the lateral displacement dd

The lateral displacement of the emergent ray can be calculated using the formula: d=tsin(θiθr)cos(θr)d = t \frac{\sin(\theta_i - \theta_r)}{\cos(\theta_r)} where:

  • t=10cmt = 10 \, \text{cm} is the thickness of the slab,
  • θi=60\theta_i = 60^\circ is the angle of incidence,
  • θr=35.55\theta_r = 35.55^\circ is the angle of refraction.

Substituting the values: d=10sin(6035.55)cos(35.55)d = 10 \cdot \frac{\sin(60^\circ - 35.55^\circ)}{\cos(35.55^\circ)} d=10sin(24.45)cos(35.55)d = 10 \cdot \frac{\sin(24.45^\circ)}{\cos(35.55^\circ)} d=100.4140.815d = 10 \cdot \frac{0.414}{0.815} d100.5085.08cmd \approx 10 \cdot 0.508 \approx 5.08 \, \text{cm}

Final Answer:

The emergent ray is displaced by approximately 5.08 cm.

Would you like a detailed breakdown or have any questions?

Here are five related questions for further practice:

  1. How would the displacement change if the slab's thickness were doubled?
  2. What would happen to the displacement if the refractive index of the slab were higher?
  3. How would the displacement be affected if the angle of incidence were reduced?
  4. If the refractive index of the slab were n=1.33n = 1.33, how would the displacement change?
  5. What is the critical angle for total internal reflection in this slab?

Tip: Always ensure angles are in the correct units (degrees or radians) when using trigonometric functions in calculations.

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Math Problem Analysis

Mathematical Concepts

Snell's Law
Trigonometry
Geometrical Optics

Formulas

Snell's Law: n₁ sin(θᵢ) = n₂ sin(θᵣ)
Lateral Displacement: d = t * (sin(θᵢ - θᵣ) / cos(θᵣ))

Theorems

Snell's Law

Suitable Grade Level

Grades 10-12