Lecture on Light Behavior: Reflection and Refraction

Introduction to Reflection

• Reflection is the phenomenon of light rays bouncing off a surface.
• On a smooth surface, the angle of incidence equals the angle of reflection, measured relative to a perpendicular.

Transition to Refraction

• Refraction occurs when light passes from one medium to another and bends rather than reflecting.
• Example scenario: light moving from a vacuum to water (or glass) leading to a change in direction.

Refraction Explained

• Incident Ray: Light entering the interface at an angle (\theta_1).
• Refracted Ray: Light changing direction at angle (\theta_2) as it enters a new medium.
• Light travels fastest in a vacuum; slower in mediums like water or glass.

Intuitive Understanding of Refraction

• Analogy with a Car: Like a car going from road to mud:
  • Car slows on mud, changes direction without steering.
  • Right side of the car reaches mud first, causing a turn.
  • In light refraction, the side in the slower medium turns first.

Snell's Law

• Snell's Law relates incident and refracted angles to the velocities of light in different media:
  • (\frac{v_2}{\sin \theta_2} = \frac{v_1}{\sin \theta_1})
• Index of Refraction (n):
  • Defined for materials as (n = \frac{c}{v}) where (c) is the speed of light in a vacuum.
  • Alternate form of Snell's Law using refraction indices:
    • (n_2 \sin \theta_2 = n_1 \sin \theta_1)

Examples and Implications

• Refraction Indices:
  • Vacuum: 1.0 (light travels at full speed (c)).
  • Air: Slightly more than 1.0.
  • Diamond: Significantly higher index, indicating much slower light speed.

Closing Remarks

• Understanding refraction provides insights into phenomena like why objects appear bent in water.
• Future videos will provide more examples and applications of Snell’s Law.