Define the principal focus of a concave mirror.

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Chapter 9 NCERT Class 10 Science SOLUTIONS

1. Define the principal focus of a concave mirror.

Question:

Define the principal focus of a concave mirror.

Answer:

The principal focus of a concave mirror is the point on its principal axis where rays parallel to the principal axis meet after reflection from the mirror.

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(All Q's of this Chapter solved)

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A doctor prescribes a rectifier lens of power +1.5 D. Find the focal length of the lens. Is the lens converging or diverging?

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Find the focal length of the lens whose power is – 2.0 D. What is the type of lens?

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An object of size 7.0 cm is placed at a distance of 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 clear focused image of the object is formed? Find the size and nature of an object.

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An object of length 0.5 cm is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position, nature and size of the image.

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The magnification of an image formed by plane mirror is +1. What does this mean?

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An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and image of the image.

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An object is placed at a distance of 15 cm from a convex lens of focal length 10 cm. Write the nature and magnification of the image.

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An object 5 cm long is placed at a distance of 25 cm from a converging lens of focal length 10 cm. Find the position, size and nature of the image formed along with the ray diagram.

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Cover the half of a convex lens with black paper. Will this lens be able to form a complete image of an object? Check your answer with the help of an experiment. Explain your observations.

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Name the mirror used for the following situations : (a) Headlight of a car (b) Side mirror/ rear mirror of a vehicle (c) Solar furnace Explain your answers.

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Using a concave mirror of focal length 15 cm, we want to form an erect image of an object. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image bigger or smaller than the object? Draw a ray diagram of the image formation for this case.

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Which of the following lenses would you prefer while reading small letters in a dictionary? (a) A convex lens with focal length of 50 cm (b) A concave lens with focal length of 50 cm (c) A convex lens with focal length of 5 cm (d) A concave lens with focal length of 5 cm

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No matter how far you stand from a mirror, your image always appears straight. The mirror probably is : (a) plane (b) only concave (c) only convex (d) either plane or convex

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The focal length of a spherical mirror is : 15 cm. The mirror is probably : (a) concave (b) convex (c) plane mirror (d) none of these

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Where do you place the object in front of a convex lens to get a real and equal size image of an object? (a) At the principal focus of the lens, (b) At twice the focal length (c) At infinity (d) Between the optical centre of the lens and the principal focus

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The image formed by a concave mirror of an object is found to be virtual, erect and larger than the object. The position of the object will be : (a) Between the principal focus and the center of curvature (b) At the center of curvature (c) Beyond the center of curvature (d) Between the pole and the principal focus of the mirror

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Which of the following materials cannot be used to make lenses? (a) Water (b) Glass (c) Plastic (d) Soil

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Find the power of a concave lens of focal length 2 m.

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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? Also, find the power of the lens.

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Define 1 dioptre of power of a lens.

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Why do we prefer a convex mirror as a rear-view mirror in vehicles?

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A concave mirror produces a three times magnified (enlarged) real image of an object placed at 10 cm in front of it. Where is the image located?

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Find the focal length of a convex mirror whose radius of curvature is 32 cm.

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Name a mirror that can give an erect and enlarged image of an object.

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The radius of curvature of a spherical mirror is 20 cm. What is its focal length

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