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Friday, December 1, 2017

CBSE CLASS 12 PHYSICS RAY OPTICS AND OPTICAL INSTRUMENTS - IMPORTANT QUESTIONS FOR BOARD EXAMS

RAY OPTICS - REFLECTION AND REFRACTION PREVIOUS YEARS BOARD QUESTIONS


cbse class 12 ray optics important questions


Numerical problems

1. Monochromatic light of wavelength 589 nm incident from air on water surface. what are the values of wavelength, frequency and speed of (a) reflected light (b) refracted light.
Refractive index of water is 1.33.
2.The Apparent depth of an object at the bottom of a tank filled with a liquid of refractive index 1.3 is 7.7 cm. what is the actual depth of the liquid in the tank?
3.An object is kept in front of a concave mirror of focal length 20 cm. The image formed is 3 times the size of object. Calculate the possible distances of the object from the mirror.
4.Use mirror formula to show that for an object lying between F and 2F of a concave mirror, a real image is formed beyond 2F
5.Find the position of object, which when placed in front of a convex mirror of focal length 20 cm, produces virtual image, which is half the size of object
6.The radius of curvature of each surface of a convex lens of refractive index 1.5 is 40 cm. Calculate its power.
7. The radius of curvature of each face of a biconvex lens, made of glass of refractive index 1.5 is 30 cm. calculate the focal length of the lens in air.
8.Glass has a refractive index of 1.5. A convex lens made of thin glass has a focal length of 20 cm  in air. It is  immersed  in water whose refractive index is 4/3. Calculate the apparent changed focal length of the lens.
9. A Double concave lens of glass of refractive index 1.5 has both radii of curvature of 40 cm. An object 2 cm high  is placed at 10 cm from the lens. Find the position, nature and size of image
10. Two thin lenses of focal lengths +10 cm and -5 cm  are kept in contact. what is the (a)focal length (b) power of combination.
11.A converging lens has a focal length of 20cm in air. It is made of  material of refractive index 1.6. If  it is immersed in a liquid of refractive index 1.3, what will be its new focal length? How does the nature of lens change if this lens is immersed in a liquid of refractive index 1.8?
12. A  double convex lens made of glass of refractive index 1.6 has it's both surfaces of equal radii of curvature of 30 cm each.An  object of 5 cm height is placed at a distance of 12.5 cm from the lens.Find the position, nature and size of image.
13. An  illuminated object and a screen are placed 90 cm apart. Determine focal length and nature of lens required to produce a clear image  on the screen, twice the size of the object.
14. A substance  has Critical Angle of 45° for yellow light. What is the refractive index?
15.Use mirror equation  to show that -
(a) A convex mirror always produces a virtual image independent of the location of object.
(b) An object placed between the pole and focus of a concave mirror produces a virtual and enlarged.


Download CBSE Class 12 Physics Previous Years Question Papers with Solutions

OPTICAL INSTRUMENTS- PREVIOUS YEARS BOARD QUESTIONS

1.    A converging lens of focal length 6.25 cm is used as a magnifying glass, if the near point of the observer is 25 cm from the eye and the lens is held close to the eye. Calculate
(i)             the distance of the object from the lens and
(ii)           the angular magnification.
2.    A compound microscope with an objective of 1.0 cm focal length and an eyepiece of 2.0 cm focal length, has a tube length of 20 cm. Calculate the magnifying power of the microscope, if the final image is formed at the near point of the eye.
3.    A compound microscope uses an objective lens of focal length 4 cm and eye lens of focal length 10 cm and object is placed at 6 cm from the objective lens
i)    Calculate magnifying power of the compound microscope if the final image is formed at the near point
ii)   Calculate the length of the compound microscope also .
4.    The total magnification produced by a compound microscope is 20, while that produced by the eyepiece alone is 5. When the microscope is focused on a certain object ,the distance between objective and eyepiece is 14 cm. Find the focal length of objective and eyepiece, if distance of distinct vision is 20 cm.
5.    The focal lengths of the objective and eyepiece of a microscope are 1.25 cm and 5 cm respectively. Find the position of the object related to the objective in order to obtain an angular magnification of 30 in normal adjustment.
6.    A small telescope has an objective lens of focal length 150 cm and an eyepiece of focal length 5 cm. If this telescope is used to view 100m high tower 3 km away. Find the height of the final image, when it is formed 25 cm away from the eyepiece.
7.    A small telescope has an objective lens of focal length 150 cm and eyepiece of focal length 5 cm. What is the magnifying power of the telescope for viewing distant objects in normal adjustment.
8.    The sum of focal length of two lenses of a  refracting telescope  is 105 cm, the focal length of 1 lens is 20 times that of the other. Determine the total magnification of the telescope when the final image is formed at infinity.
9.    The focal length of objective of an astronomical telescope is 1.0 m. If the magnifying power of the telescope is 20, find the focal length of the eyepiece and the length of the telescope for the relaxed eye .


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