# Unit 3: Light and Optical Instruments J. Pulickeel SPH3U1 November 2008 Lesson 3: Refraction and Snells Law.

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Unit 3: Light and Optical Instruments J. Pulickeel SPH3U1 November 2008 Lesson 3: Refraction and Snells Law

Reflecting on Reflections Reflections occur when light rays bounce off objects. We can predict the direction in which reflected light rays travel by using the laws of reflection 1.The angle of reflection will ALWAYS equal the angle of incidence 2.The incident ray, the normal and the reflected ray are all in the same plane

YAY!!! MIRRORS!!!!

Mirror, Mirror on the Wall

What happens in Water? In water, objects often dont appear to be where they should be. Refraction is the bending of light when it travels from one medium to another. Light bends because it changes speed when it moves between materials that have different densities Density tells you how closely packed the particles of a material are

Faster than a Speeding Bullet Light travels at 300 000 km/s in air!!! It slows down to 200 000 km/s in glass. It slows down to 165 000 km/s in diamond. Light slows down in denser materials! Well get you at the lake Wow, you guys are slow!

Why does light slow down? Imagine a car on a road. If one tire hits the gravel, it will cause that tire to slow down. Because it is moving slower than the other tires, the other tires will cover more distance per second. This will cause the car to turn into the gravel. Things will turn towards the more dense medium.

Speed of Light Vacuum299,792 km/sec Air299,704 km/sec Water224,900 km/sec Alcohol220,435 km/sec Glass199,861 km/sec Salt194,166 km/sec Diamond123,932 km/sec Silicon74,761 km/sec Not dense Very Dense

Around a Bend with Light When light travels from one medium to a denser one (air to water), it will bend towards the normal.

Im directly under the sun….. Now!

Around a Bend with Light When light travels from a dense medium to a lighter one (water to air), it will bend away the normal. Which One??? Normal

Partial Reflection and Refraction When light is refracted, it can cause the ray to split into two. Some will be refracted, and some will be reflected back into the medium. This called partial reflection and refraction. Click here for animation (show laser in water)

Imagine you are in a darkened room looking out a window. Someone turns on the light in the room. Will this help you see out the window better ? Explain why using a ray diagram Image of light window light

As light travels from medium A into medium B, the angle of incidence is 36° and the angle of refraction is 21° a) Does light bend towards or away from the normal? Draw a diagramto prove this. b) What is the angle of the reflection of the partially reflected ray? Incident ray Reflected ray Refracted ray 36° 21°

Around a Bend with Light When light travels from a dense medium to a lighter one (water to air), it will bend away the normal.

Angle of Refraction Incident Ray Angle of incidence Refracted ray Angle of Refraction Incident RayAngle of incidence Refracted ray Angle of Refraction Normals

Light being Refracted Light travels fastest in a vacuum because there are no medium to slow it down. Other mediums produce different speeds, its always less than in a vacuum. The ratio of the speed of light in a vacuum (c) to the speed of light in a given material (v) is called the index of refraction (n)

Calculate the speed of light in zircon in (a) m/s and (b) in terms of the speed of light.

Snells Law In the 1600s Snell determined that the angle of incidence and the angle of refraction were directly proportional. By introducing a constant, we can make this an equation. Through experimentation, it was determined that the constant was n. Therefore This however assumes that the incident ray began in a vacuum…

The Laws of Refraction 1. 2. The incident ray and the refracted ray are on opposite sides of the normal at the point of incidence, and all three are in the same plane.

General Equation of Snells Law If a ray is originating in medium 1 and continuing into medium 2, the general equation of Snells Law can be written as

Light travels from crown glass (g) into water (w). The angle of incidence in crown glass is 40.0°. What is the angle of refraction in water

Homework 9.3 Q4 9.4 Q1,2,4 9.5Q2-4 Note! Lab Tomorrow. Read Investigation 9.5.1 (not Activity). Submitted (?) - Hand written, as group on Mon/Tues ? Problem Set Posted. Due Friday December 4 Test Dec 8 th on Chapter 9-10 Project Dec. 14 (maybe 1-2 days later) …

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