The speed of light in a medium is calculated using the formula v = c/n, where v is the speed of light in the medium, c is the speed of light in vacuum, and n is the refractive index of the medium. For glass with a refractive index of 1.50, the speed of light in glass is (3 × 10⁸)/1.5 = 2 × 10⁸ m/s.

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## Introduction to Light Speed in Different Media

Fundamental Properties of Light: The speed of light varies when it travels through different media. In a vacuum, it travels at its maximum speed, but this speed decreases when light passes through any material medium due to interactions with the medium’s particles.

### Speed of Light in Vacuum

Maximum Velocity of Light: In a vacuum, light travels at a speed of approximately 3 × 10⁸ meters per second (m/s). This speed is considered a fundamental constant of nature and is the fastest speed at which energy or information can travel.

#### Refractive Index of Glass

Optical Density Indicator: The refractive index of a medium is a measure of how much the speed of light is reduced inside the medium compared to its speed in a vacuum. For glass, the refractive index is given as 1.50, indicating that light travels slower in glass than in a vacuum.

##### Calculating Light Speed in Glass

Applying the Formula: The speed of light in a medium can be calculated using the formula v = c/n, where v is the speed of light in the medium, c is the speed of light in a vacuum, and n is the refractive index of the medium.

###### Result of the Calculation

Determining the Speed in Glass: Substituting the known values into the formula,
v = (3 × 10⁸)/1.5, we find that the speed of light in glass is approximately 3 × 10⁸ m/s.

Implications in Optics: This reduced speed of light in glass has significant implications in optics, affecting how light beams bend (refract) and how lenses and prisms in optical devices manipulate light. Understanding these principles is crucial in designing various optical instruments and technologies.

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Questions of 10th Science Chapter 9 in Detail

 Define the principal focus of a concave mirror. The radius of curvature of a spherical mirror is 20 cm. What is its focal length? Name a mirror that can give an erect and enlarged image of an object. Why do we prefer a convex mirror as a rear-view mirror in vehicles? Find the focal length of a convex mirror whose radius of curvature is 32 cm. A concave mirror produces three times magnified (enlarged) real image of an object placed at 10 cm in front of it. Where is the image located? A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why? Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass? Find out, from Table, the medium having highest optical density. Also find the medium with lowest optical density. You are given kerosene, turpentine and water. In which of these does the light travel fastest? The refractive index of diamond is 2.42. What is the meaning of this statement? Define 1 dioptre of power of a lens. A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Find the power of a concave lens of focal length 2 m. We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? Name the type of mirror used in the following situations. (a) Headlights of a car. (b) Side/rear-view mirror of a vehicle. (c) Solar furnace. One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. What is the position, size and the nature of the image formed. A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image. The magnification produced by a plane mirror is +1. What does this mean? An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image, its nature and size. An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focussed image can be obtained? Find the focal length of a lens of power – 2.0 D. What type of lens is this? A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?