Topicma4e454ec7152f4ac_1528449000663_0Topic

The phenomenon of refraction of light at the boundaryboundaryboundary of media

Levelma4e454ec7152f4ac_1528449084556_0Level

Second

Core curriculumma4e454ec7152f4ac_1528449076687_0Core curriculum

IX. Optics. The student:

6) describes qualitatively the phenomenon of refraction at the boundary of two different media differing in the speed of light propagation; indicates the direction of refraction.

Timingma4e454ec7152f4ac_1528449068082_0Timing

45 minutes

General learning objectivesma4e454ec7152f4ac_1528449523725_0General learning objectives

Describes the phenomenon of refraction at the boundary of two media.

Key competencesma4e454ec7152f4ac_1528449552113_0Key competences

1. Explains the phenomenon of total internal reflectiontotal internal reflectiontotal internal reflection.

2. Reconstructs the path of a light ray through a plane parallel plateplane parallel plateplane parallel plate.

Operational (detailed) goalsma4e454ec7152f4ac_1528450430307_0Operational (detailed) goals

The student:

- explains the phenomenon of refraction of light on the boundaryboundaryboundary of two media differing in the speed of light propagation,

- reconstructs the path of a light ray passing through media differing in optical density.

Methodsma4e454ec7152f4ac_1528449534267_0Methods

1. Discussion.

2. Text analysis.

Forms of workma4e454ec7152f4ac_1528449514617_0Forms of work

1. Individual work.

2. Group work.

Lesson plan

Introductionma4e454ec7152f4ac_1528450127855_0Introduction

Recall the law of refraction.

What does it mean that one medium is more optically dense than the other?

Procedurema4e454ec7152f4ac_1528446435040_0Procedure

The phenomenon of light refraction is always accompanied by the phenomenon of light reflection.

Part of the light beam refracts, and part of the light beam reflects off the boundary of the two media. Therefore, for example, standing on the edge of the lake, we can see our reflection or shimmering waves, and while diving, we can observe what is happening under its surfacesurfacesurface.

For certain values of the angle of incidenceangle of incidenceangle of incidence, the light rays travelling in a more optically dense medium do not refract, but are reflected fully off the boundaryboundaryboundary of the two media.

Task 1

Watch the slideshow and see examples of total internal reflectiontotal internal reflectiontotal internal reflection.

[Slideshow 1]

The phenomenon of total internal reflection occurs when the light ray passes from a more optically dense medium to a less optically dense medium. The more optically dense the medium, the lower the speed of light in it.ma4e454ec7152f4ac_1527752256679_0The phenomenon of total internal reflection occurs when the light ray passes from a more optically dense medium to a less optically dense medium. The more optically dense the medium, the lower the speed of light in it.

If we gradually increase the angle of incidence of the light ray in the more optically dense medium, then we notice that for a certain angle, called the critical angle, the refracted ray begins to travel exactly on the boundary of the two media. If we continue to increase the angle of incidence, then we will no longer observe the phenomenon of refraction of the light ray, only its total internal reflection.ma4e454ec7152f4ac_1527752256679_0If we gradually increase the angle of incidence of the light ray in the more optically dense medium, then we notice that for a certain angle, called the critical angle, the refracted ray begins to travel exactly on the boundary of the two media. If we continue to increase the angle of incidence, then we will no longer observe the phenomenon of refraction of the light ray, only its total internal reflection.

Task 2

Familiarize yourself with the slideshow and follow how the phenomenon of total internal reflectiontotal internal reflectiontotal internal reflection occurs.

[Slideshow 2]

The relation between the angle of incidenceangle of incidenceangle of incidence and the angle of refractionangle of refractionangle of refraction is shown in the graphgraphgraph below. There are shown curves for various media: air‑to‑glass, air‑to‑water, water‑to‑glass.

Critical angles values are different for different media.

[Illustration 1]

Task 3

Read what the critical angle is for the media shown in the graphgraphgraph. Compare your reading with the solution below.

Answer:

Critical angle for:

- glass to air: 41°,

- water to air: 49°,

- glass to water: 60,5°

The light rays on their path meet different media and many times pass their boundaries, e.g. the passage of a light ray through the window glass (air‑to‑glass and glass‑to‑air), light illuminating the interior of the aquarium (air‑to‑glass and glass‑to‑water).ma4e454ec7152f4ac_1527752263647_0The light rays on their path meet different media and many times pass their boundaries, e.g. the passage of a light ray through the window glass (air‑to‑glass and glass‑to‑air), light illuminating the interior of the aquarium (air‑to‑glass and glass‑to‑water).

A simple element that allows tracing the behaviour of the light beam is a plane parallel plate. It is an optically homogeneous medium for the light. Most often it is made of glass or acrylic. It is important that such a plate has at least two flat sides parallel to each other.ma4e454ec7152f4ac_1527752263647_0A simple element that allows tracing the behaviour of the light beam is a plane parallel plate. It is an optically homogeneous medium for the light. Most often it is made of glass or acrylic. It is important that such a plate has at least two flat sides parallel to each other.

Task 4

Make a drawing in the notebook according to the diagram below. Using a protractor and a ruler, draw the exact path of the light ray passing through the plates. Read the necessary angles from the graphgraphgraph above.

At what angle is the light ray coming out of the plate directed? What conclusion can you draw?

[Illustration 2]

Answer:

The light ray coming out of the plate is parallel to its previous direction. Its angle of refractionangle of refractionangle of refraction after leaving the water/glass is 55°.

Lesson summaryma4e454ec7152f4ac_1528450119332_0Lesson summary

The light ray passing from a more optically dense medium to a less optically dense medium can be totally reflected.

The light ray passing through the plane parallel plateplane parallel plateplane parallel plate retains its original direction.

Selected words and expressions used in the lesson plan

angle of incidenceangle of incidenceangle of incidence

angle of refractionangle of refractionangle of refraction

boundaryboundaryboundary

graphgraphgraph

plane parallel plateplane parallel plateplane parallel plate

surfacesurfacesurface

total internal reflectiontotal internal reflectiontotal internal reflection