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Chapter Analysis
Advanced27 pages • EnglishQuick Summary
The chapter on Ray Optics and Optical Instruments explores the fundamental principles of light behavior such as reflection, refraction, and dispersion. It discusses the laws governing these phenomena and applies them to various optical instruments like lenses and mirrors. The chapter also covers practical applications, including optical instruments such as microscopes and telescopes, illustrating image formation and magnification principles. Overall, the text combines theoretical and practical aspects to give students a comprehensive understanding of ray optics and its uses in technology.
Key Topics
- •Reflection and refraction of light
- •Laws of reflection and refraction
- •Optical instruments like microscopes and telescopes
- •Image formation by lenses and mirrors
- •Total internal reflection and its applications
- •Transmission and focusing of light through lenses
Learning Objectives
- ✓Understand the laws of reflection and refraction and apply them to optical scenarios.
- ✓Identify and describe the functioning of optical instruments such as microscopes and telescopes.
- ✓Interpret the principles of image formation in various types of mirrors and lenses.
- ✓Explain total internal reflection and its significance in technologies like optical fibers.
- ✓Analyze and solve problems related to the behavior of light in different media.
Questions in Chapter
A small candle, 2.5 cm in size is placed at 27 cm in front of a concave mirror of radius of curvature 36 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? Describe the nature and size of the image. If the candle is moved closer to the mirror, how would the screen have to be moved?
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A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror.
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A tank is filled with water to a height of 12.5 cm. The apparent depth of a needle lying at the bottom of the tank is measured by a microscope to be 9.4 cm. What is the refractive index of water? If water is replaced by a liquid of refractive index 1.63 up to the same height, by what distance would the microscope have to be moved to focus on the needle again?
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Figures 9.27(a) and (b) show refraction of a ray in air incident at 60° with the normal to a glass-air and water-air interface, respectively. Predict the angle of refraction in glass when the angle of incidence in water is 45° with the normal to a water-glass interface [Fig. 9.27(c)].
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A small bulb is placed at the bottom of a tank containing water to a depth of 80cm. What is the area of the surface of water through which light from the bulb can emerge out? Refractive index of water is 1.33. (Consider the bulb to be a point source.)
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A prism is made of glass of unknown refractive index. A parallel beam of light is incident on a face of the prism. The angle of minimum deviation is measured to be 40°. What is the refractive index of the material of the prism? The refracting angle of the prism is 60°. If the prism is placed in water (refractive index 1.33), predict the new angle of minimum deviation of a parallel beam of light.
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Double-convex lenses are to be manufactured from a glass of refractive index 1.55, with both faces of the same radius of curvature. What is the radius of curvature required if the focal length is to be 20cm?
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A beam of light converges at a point P. Now a lens is placed in the path of the convergent beam 12cm from P. At what point does the beam converge if the lens is (a) a convex lens of focal length 20cm, and (b) a concave lens of focal length 16cm?
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An object of size 3.0cm is placed 14cm in front of a concave lens of focal length 21cm. Describe the image produced by the lens. What happens if the object is moved further away from the lens?
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What is the focal length of a convex lens of focal length 30cm in contact with a concave lens of focal length 20cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.
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Additional Practice Questions
Explain why the speed of light is considered the ultimate speed limit in the universe.
mediumAnswer: According to Einstein’s theory of relativity, the speed of light in vacuum (c = 3 × 10^8 m/s) is the maximum speed at which all energy, matter, and information in the universe can travel. This is because, as an object moves closer to the speed of light, its mass increases exponentially, requiring infinite energy to reach or exceed the speed of light, which is unattainable with finite energy resources.
How do optical fibers utilize the principle of total internal reflection?
easyAnswer: Optical fibers are thin strands of glass or plastic that transmit light between two ends of the fiber, using the principle of total internal reflection. Light rays entering the fiber are reflected internally with minimal loss of signal, allowing efficient transmission of data over long distances. This occurs because the core of the fiber has a higher refractive index compared to the surrounding cladding, ensuring that the light is reflected back into the core at every reflection.
Illustrate how a simple microscope works to magnify objects.
easyAnswer: A simple microscope uses a single convex lens to magnify small objects. When an object is placed at a distance less than the focal length of the lens, a virtual, erect, and magnified image is formed on the same side of the lens. This setup allows details of small objects to be viewed more clearly, making it useful for tasks such as reading fine print or examining small insects.
What are the differences between real and virtual images and how are they formed?
hardAnswer: Real images are formed when light rays converge and can be displayed on a screen, whereas virtual images occur where light rays appear to diverge or do not actually meet. Real images are inverted, and formed on the opposite side of the object in lenses, or same side of the object in mirrors. Virtual images, in contrast, are erect and located on the same side as the object in lenses and opposite side in mirrors. Real images are formed by concave mirrors and convex lenses when the object is outside the focal length. Virtual images are formed by convex mirrors, concave lenses, and typically by a magnifying glass (convex lens) when the object is within the focal length.
Describe the principles of refraction and how they apply to lenses.
mediumAnswer: Refraction is the bending of light when it transitions between media of different densities, governed by Snell's law (n1 sin θ1 = n2 sin θ2). For lenses, refraction causes light rays to change direction, contributing to focusing or diverging effects. Convex lenses converge light rays to meet at a point, forming real images. Concave lenses, however, cause light rays to diverge, forming virtual images.