Physics Chapter on Light Refraction

Unit 6: Light - Week 21

• Topic: Reflection and Refraction

Learning Objectives

• Students will be able to describe how light reflects from a plane mirror.
• Students will understand the laws of reflection.
• Students will be able to draw ray diagrams to show light reflection.
• Students will understand refraction of light.

Nature of Light

• Light is a form of energy that allows us to see.
• Light travels in straight lines.
• Light travels at a very high speed (3.0 x 10⁸ ms^-1) in a vacuum.
• Luminous sources emit light, such as the sun, stars, candles, and lamps.

Reflection of Light

• We see reflections in mirrors.
• Reflections in a plane mirror are upright, the same size, and same color as the object.
• Moving closer to a mirror causes the image to move closer. Moving away causes the image to move away.
• Mirror images are virtual because there is nothing behind the mirror.
• Images projected onto a screen are real images.
• A mirror image is laterally inverted.

Reflection of Light (1) & (2)

• Reflection of Light (1): Shows the incoming ray, the reflected ray, and the normal to the mirror surface.
• Reflection of Light (2): Demonstrates and defines the angle of incidence (i) and angle of reflection (r). The angle of incidence always equals the angle of reflection.

Types of Reflection

• Regular Reflection: Parallel incident rays reflect as parallel rays, as seen in a plane mirror, producing a clear image.
• Diffuse Reflection: Incident rays reflect in different directions. This is how we see most surfaces.

Laws of Reflection

• Law 1: The angle of incidence (i) is equal to the angle of reflection (r).
• Law 2: The incident ray, reflected ray, and the normal to the surface all lie in the same plane.

Measuring Angles of Incidence and Reflection

• Using a protractor, measure the angles of incidence and reflection.

Making Measurements

• Techniques for precisely measuring angles of incidence and reflection using a protractor and a ray diagram.

Refraction of Light

• A pencil appears bent or broken when partially submerged in water due to refraction.

• Refraction occurs when light traveling from one transparent medium to another, such as air to water, changes direction.

• The change in direction occurs at the boundary between the two media.

Refraction

• Angle of incidence is the angle between the incident ray and the normal to the surface.
• Angle of refraction is the angle between the refracted ray and the normal to the surface.

Refraction (From air into water/glass)

• Light bends towards the normal when traveling from a less dense to a denser medium (e.g., air to water or air to glass).

Refraction (From water/glass into air)

• Light bends away from the normal when traveling from a denser to a less dense medium (e.g., water to air or glass to air).

Why Does Refraction Happen?

• The speed of light changes when it travels through different materials. Denser materials make light slow down.
• The ratio of the speed of light in a vacuum to the speed of light in a medium is the refractive index.

Applications of Refraction

• Lenses use refraction to form images.
• Eyeglasses (spectacles) for vision correction rely on the principles of refraction.
• Refraction is in peepholes, cameras, movie projectors, and telescopes.

Application of Refraction

• Pools look shallower due to the refraction of light.
• A spoon submerged in water appears bent.
• Refraction is how we perceive objects in different media.

Speed of Light and Refraction

• Light's speed changes when passing through different mediums.
• This speed change relates to the medium's density.
• The refractive index quantifies this relationship.

Applications of Refraction

• Lenses use refraction to form images.
• Eyeglasses correct vision problems.
• Refraction is used in peepholes, cameras, and telescopes.

Concept Check Questions

• Included questions about reflection and refraction. Answers are not provided as that would require a separate document.