# Class 10 Physics Geometrical Optics i. Which of the following quantity is not changed during refraction of light?(a) its direction(b) its speed(c) its frequency(d) its wavelength

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##### i. Which of the following quantity is not changed during refraction of light?(a) its direction(b) its speed(c) its frequency(d) its wavelength

12.8. An object 4 \mathrm{~cm} high is placed at a distance of 12 \mathrm{~cm} from a convex lens of focallength 8 \mathrm{~cm} . Calculate the position and size of the image. Also state the nature of the image.Ans. (24 \mathrm{cm} 8 \mathrm{~cm} image is real inverted and magnified)

7. What is the difference between astronomical and terrestrial telescopes?

12.16. A coin is placed at a focal point of a converging lens. Is an image formed? What is its nature?

12.1. An object 10.0 \mathrm{~cm} in front of a convex mirror forms an image 5.0 \mathrm{~cm} behind the mirror. What is the focal length of the mirror?Ans.

12.2. Describe the following terms used in reflection:(i) normal (ii) angle of incidence (iii) angle of reflection

x. The critical angle for a beam of light passing from water into air is 48.8 degrees. This means that all light rays with an angle of incidence greater than this angle will be(a) absorbed(b) totally reflected(c) partially reflected and partially transmitted(d) totally transmitted

12.6. An image is produced by a concave mirror of focal length 8.7 \mathrm{~cm} . The object is 13.2 \mathrm{~cm} tall and at a distance 19.3 \mathrm{~cm} from the mirror. (a) Find the location and height of the image. (b) Find the height of the image produced by the mirror if the object is twice as far from the mirror.Ans. [(a) 15.84 \mathrm{~cm} 10.83 \mathrm{~cm} (b) 5.42 \mathrm{~cm} ]

12.10. A convex lens of focal length 6 \mathrm{~cm} is to be used to form a virtual image three times the size of the object. Where must the lens be placed?Ans.

4. Why is a convex lens of small focal length preferred for a magnifying glass?

12.1. What do you understand by reflection of light? Draw a diagram to illustrate reflection at a plane surface.

5. A parallel light beam is diverged by a concave lens of focal length- 12.5 \mathrm{~cm} and then made parallel once more by a convex lens of focal length 50 \mathrm{~cm} . How far are the two lenses apart.(Ans. 37.6 \mathrm{~cm} )

9. Explain the construction and calculate the magnifying power of Gallean telescope.

12.6. What is meant by refractive index of a material? How would you determine the refractive index of a rectangular glass slab?

12.5. Why is the drivers side mirror in many cars convex rather than plane or concave?

12. A compound microscope has an objective with a focal length of 10 \mathrm{~mm} and a tube 100 \mathrm{~mm} long. An Image is produced 250 \mathrm{~mm} from the eye plece when the object is 12 \mathrm{~mm} from the objective. What is the angular magniflcation?

vi. Which type of image is formed by a concave lens on a screen?(a) inverted and real(b) inverted and virtual(c) upright and real(d) upright and virtual

12.10. Why do we use refracting telescope with large objective lens of large focal length?

14. A convex lens forms Image of an object on a fixed screen 20 \mathrm{cm} from the lens. On moving the lens 60 \mathrm{~cm} towards the obJect the Image is again formed on the screen. What is the focal length of the lens?

12.21. Define the terms resolving power and magnifying power.

12.20. Describe the passage of light through a glass prism and measure the angle of deviation.

Example 10.1A chess plece 4 \mathrm{~cm} high is located 10 \mathrm{~cm} from the converging lens whose forcal length is 20 \mathrm{~cm} . What is the nature size and location of the Image?

2. A convex lens has a focal length of 10 \mathrm{~cm} . Determine the \mathrm{im} age distances when an object is placed at the following distances from the lens. 50 \mathrm{~cm} 20 \mathrm{~cm} 15 \mathrm{~cm} 10 \mathrm{~cm} and 5 \mathrm{~cm}

Example 10.7 An astronomical telescope has an objective lens whose power Is 2 dioptres. This lens is placed 60 \mathrm{~cm} from the eye plece. When the telescope is adjusted for minimum eye strain. Calculate the angular magnification of the telescope.

12.22. Draw the ray diagrams of(i) simple microscope

12.3. State laws of reflection. Describe how they can be verified graphically.

6. How is the magnifying power of a (i) telescope and

Example 10.3 A convex lens of focal length 20 \mathrm{~cm} is used to form an erect Image which is twice as large as the object. Find the position of the object?

Sxample 10.6A microscope has an objective of 10.0 \mathrm{~mm} focal length and eye plece of 25 \mathrm{~mm} focal length. What is the distance between the lenses and what is the magniflcation ff the object is in sharp focus when It is 10.5 \mathrm{~mm} from the objective?