Light (continued)
Overview
A straw looks bent in a glass of water, a diamond sparkles with rainbow fire, and a tiny camera lens captures a whole landscape. All of these come from one idea: light changes speed and bends when it crosses between materials. Control that bending and you can focus, magnify, trap light in a fibre, or split white light into its colours.
In this lesson you will master refraction and refractive index, the critical angle and total internal reflection (with its use in optical fibres), the action of converging and diverging lenses, ray diagrams for real and virtual images, the dispersion of white light by a prism, and the seven colours of the spectrum. Every calculation is shown with its equation, substitution and units.
Objectives
- [Core] Define refraction as the change in direction of a light ray passing from one medium to another
- [Core] Define and use the terms normal, angle of incidence and angle of refraction using ray diagrams
- [Core] Describe the passage of light through a transparent material (limited to the boundaries between two media only)
- [Core] Describe the action of a thin converging lens on a parallel beam of light and know that rays of light from an object at distance can be assumed to be parallel
- [Core] Define and use the terms principal axis, principal focus (focal point) and focal length
- [Core] Interpret ray diagrams for the formation of an image by a thin converging lens, limited to real images
- [Core] Describe the characteristics of an image using the terms enlarged / same size / diminished and upright / inverted
- [Core] Describe the dispersion of light as illustrated by the refraction of white light by a glass prism
- [Core] Know the seven colours (red, orange, yellow, green, blue, indigo, violet) of the visible spectrum in order of frequency and in order of wavelength
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Flashcards
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Light (continued). Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- When light passes from air into glass it bends A. away from the normal and speeds up B. towards the normal and slows down C. towards the normal and speeds up D. along the surface Answer: B
- A glass has refractive index 1.5. Light travels in it at (speed in air = 3.0 x 10^8 m/s) A. 4.5 x 10^8 m/s B. 3.0 x 10^8 m/s C. 2.0 x 10^8 m/s D. 1.5 x 10^8 m/s Answer: C
- The critical angle of a material of refractive index 2.0 is closest to (sin c = 1/n) A. 24 degrees B. 30 degrees C. 42 degrees D. 60 degrees Answer: B
- An object placed beyond 2F from a converging lens forms an image that is A. virtual, upright, enlarged B. real, inverted, diminished C. real, upright, same size D. virtual, inverted, enlarged Answer: B
- Which colour of the visible spectrum is refracted the most by a prism? A. red B. yellow C. green D. violet Answer: D
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