1. The Speed of Light Changes:
- Light travels at different speeds in different mediums. For example, light travels faster in air than in water.
- When light enters a denser medium (like water), it slows down. Conversely, it speeds up when entering a less dense medium (like air).
2. The Direction of the Ray Changes:
- Because the speed of light changes, the direction of the light ray also changes. This change in direction is called refraction.
- The amount of bending depends on:
- The angle at which the light ray hits the surface.
- The indices of refraction of the two substances. The index of refraction is a measure of how much light slows down in a particular medium.
3. Snell's Law:
- Snell's Law describes the relationship between the angles of incidence and refraction, and the indices of refraction of the two media:
- n₁ * sin(θ₁) = n₂ * sin(θ₂)
- n₁ and n₂ are the indices of refraction of the two substances.
- θ₁ is the angle of incidence (angle between the incoming light ray and the normal to the surface).
- θ₂ is the angle of refraction (angle between the refracted light ray and the normal to the surface).
Examples of Refraction:
* A straw in a glass of water appears bent: This is because light from the straw travels through water and then through air, causing it to bend.
* Rainbows: Sunlight is refracted as it passes through raindrops, separating the light into different colors.
* Lenses in eyeglasses and cameras: Lenses use refraction to focus light and correct vision problems.
Important Note:
- If the light ray hits the surface at a 90-degree angle (perpendicular), it will not bend.
- If the light ray travels from a denser medium to a less dense medium, and the angle of incidence is greater than the critical angle, total internal reflection occurs, where all the light is reflected back into the denser medium.
