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Subject:

science-physics

Class:

class VIII

Key Concepts

angle of incidence, angle of refelection, blind spot, braille, cones, cornea, diffused/ irregular refelection, dispersion, incident rays, iris, kaleidoscope, lateral inversions, laws of reflection, pupil, reflected rays, reflection

essential questions

1. How does light travel?
2. What aspects of light change as light passes from one medium to another?

Remembering:

  1. What is angle of deviation?
  2. Write the laws of reflection.
  3. Define lateral inversion.
  4. How many cells are there in a Braille Characters?  a) 12   b) 9    c) 3    d) 6
  5. Which of the following works on the concept of multiple reflections? a) telescope b) binoculars  c) kaleidoscope  d) sunglasses
  6. Which of the following is a tactile aid?  a) stylus  b) tactile strip  c) braille script   d) all of the above
  7. The human eye can clearly see up to which distance? a) infinity  b) 1000 km  c) 100 km  d) 10 km
  8. Cyan, yellow and magenta are: a) primary colors  b) white colors  c) secondary color   d) tertiary colors
  9.  Reflection obtained from a smooth surface is called a: a) regular reflection   b) irregular reflection c) both a and b d) none
  10. Way of light is always in a: a) bend path  b) straight line  c) convergent path  d) divergent path
  11. Angle between incident ray and normal ray is called angle of: a) reflection b) refraction c) transmission d) incident
  12. An instrument which enables us to see things which are too small to be seen with naked eye is called: a) microscope b) telescope c) kaleidoscope   d) periscope
  13. In swimming pools they appear shallower than they are actual because of: a) reflection  b) refraction  c) both a and b  d) none
  14. A spinning of rainbow colors disc will produce:  a)multi shape spin  b) white light  c) dispersed light  d) red light
  15. Kind of shadow depends on size and position of: a) object   b) light source  c) both a and b   d) sun
  16. When speed decreases light bend towards: a) normal ray  b) incident ray   c) reflected ray   d) no ray
  17. Parallel light beam strikes a smooth surface producing parallel:  a) image   b) beams   c) rays    d) particles
  18. Shadows are formed due to way of light which always travel in:  a) straight line   b) divergent line   c) convergent line   d) clusters
  19. The color in the Iris of a person is green, then what color will be the color of his eye:  a) green   b) dark brown   c)  black   d) blue
  20. Concave lens is also known as : a) converging lens  b) diverging lens  c) dispersing lens   d) conducting lens
  21.  Concave lens: a) shrinks the image  b) magnifies the image   c) sharpens the images   d) increases the contrast of image
  22. What is the nature of the image formed on the retina of human eye of an object: a) virtual and erect  b) virtual and inverted  c) real and erect  d)  real and inverted
  23. In concave lenses, a distant object appears: a) upright   b) virtual   c) magnified  d) inverted
  24. An example of object that uses concave lenses, is:  a) contact lenses   b) telescope   c) spectacles   d) microscope
  25. What is the power of concave lens?  a) positive   b) negative   c) both   d) none of the above
  26. Which glasses or lens are used to correct the short sighted eye defect? a) lens   b) convex lens    c) bipolar lens    d) None of the above
  27.  In projectors which lenses are used? a) convex lens  b) concave lens   c) bipolar lens   d) both a and b
  28. Dental mirror is what type of a mirror? a) convex mirror  b) concave mirror  c) plane mirror  d) both (b) and (c)

understanding:

  1. What is refractive index?
  2. What is lateral displacement? Show it with a diagram.
  3. What is the difference between dispersion and spectrum?
  4. Write the difference between diffused and regular reflection.
  5. What are convex and concave lenses? Differentiate between the two.
  6. Draw a labelled diagram of human eye.
  7. What are the various ways to take care of eyes?
  8. Write difference between: a) optical center & center of curvature  b) principal focus and focal length
  9. Explain the difference between Myopia and hyper metropia using diagrams.
  10. What type of a mirror is used in anti-shop-lifting-devices? a) Concave mirror   b) Convex mirror   c) Plane mirror   d) None of the above
  11. What makes an object visible: a) absorption of light by an object   b) reflected light from the object   c) total internal reflection taking in an object   d) refracted light from the object
  12. What is the phenomenon of light bouncing back into the same medium: a) reflection  b) refraction  c) dispersion  d) splitting
  13. What is the perpendicular line drawn at any point on a mirror is called: a) incident ray  b) reflected ray  c) normal  d) image
  14. Which of the following
  15. Due to which phenomena the stick if immersed in water appears to be bent? a) Reflection  b) Dispersion   c) Refraction   d) Scattering
  16. Due to which phenomena light rays emerging from a cinema machine spread wide on the screen? a) dispersion   b) diffraction    c) scattering   d) refraction
  17. What happens in lateral inversion: a) the right side of the object will be on the right side of the image  b)  the left side of the object will be on the left side of the image  c) tip of the object will be on the left side of the image  d)  right side of the object will be on the left side of the image
  18. True or false:  a) Speed of light is dependent on a medium  b) Water is more optically denser than air but less than glass
  19. Fill in the blanks:  a) When a ray of light travels obliquely from a denser medium to a rarer medium it ____ _______ from the normal.  b) The angle of incidence is ________ than the angle of refraction when ray travels obliquely from denser medium to rarer medium c) The angle of incidence is _______ the angle of refraction when ray of light travels straight from any medium d) For a ray of light travelling from one medium to another, the change in its speed is the cause for the change in its __________
  20. Draw a correct path of light for ray of light travelling from Air to Glass.
  21. Draw a correct path of light for the ray of light travelling from Air to glass slab and then air.

Application:

  1. A toy is placed at 10 cm in front of a plane mirror. What is the distance of image from the mirror? a) 20 cm b) 40 cm  c) 10 cm  d) 30 cm
  2. A candle is 30 cm high. What is the height of its image in a plane mirror? a) 10 cm b) 15 cm  c) 30 cm  d) 45 cm
  3. Why the color of the ocean appears blue? a) Because the sunlight falling on it is reflected  b) Because the sunlight falling on it is refracted  c) Because the sunlight falling on it is absorbed  d) Because the sunlight falling on it is scattered
  4. In the case of a concave mirror, the image of an object is: a) real, erect and diminished when the object lies beyond the center of curvature  b) real, inverted and of the same size as the object when it lies between the center of curvature and focus  c) real, inverted and diminished when the object lies beyond the center of curvature  d) not real, large and non proportional
  5. To increase the magnifying power of a telescope, the focal length of:  a) objective lens should be increased  b) objective lens should be decreased  c) eye-piece lens should be increased  d) eye-piece lens should be decreased
  6. Y is a surface that cannot produce clear images. What is Y: a) rough surface   b) ideal surface  c) smooth surface  d) smooth but curved surface
  7. How many images are obtained when plane mirrors are arranged parallel to each other: a) single image  b) two images  c) infinite number of images  d) zero images
  8. If the angle of incidence is 80°, what will be the angle of reflection: a) 80°   b) 100°  c) 160°  d) 20°
  9. When the angle between two plane mirrors is 60º, how many images will be formed by the mirror: a) 5   b) 6  c) 7  d) 8
  10. If the angle of incidence is 50°, then calculate the angle between the incident ray and reflected ray: a) 50° b)100°  c) 130°  d) 80°
  11. In a periscope how are the reflecting mirrors arranged: a) perpendicular to each other  b) parallel to each other  c) at an angle of 90°  d) at an angle of  60°
  12. The characteristics of an eye disease are given below: 1. eye sight become foggy  2. eye lens becomes cloudy  3. there is a loss of vision in which of the following are the above characteristics observed: a) myopia  b) presbyopia  c) hypermetropia  d) cataract
  13. Why does a swimming pool appears shallower than its real depth? Explain the principle behind it?
  14. Why do stars twinkle at night? Why do stars near the horizon twinkle more than the stars that are overhead? Why planets not twinkle?
  15. Ray of light reflected at a plane mirror. Solve by showing in through a diagram.  a) Incident ray =60° then reflected ray =    ?  b) Incident ray=45° then reflected ray=?  c) Incident ray= 90° then reflected ray=?
  16. An optician holds a test card 50cm behind from the patient. The patient then looks in the plane mirror which is 100cm away. How far away from the patient’s eyes is the image of the test card?
  17. Why do SLR cameras and sophisticated binoculars use prism to capture the image?
  18. United football club are playing an evening match. The team’s jersey has blue and white stripes. What color would the stripes appear under flood lights which produce a yellow light?
  19. Match the column 1 with column II and column III

Column I (Position of the object)                      Column II( Position of the image)         Column III( Type of image)

a) Object beyond 2F at 2F                                              Real                                                               inverted, large

b) Object at 2 F Same side as the object                      Virtual                                                            erect, magnified

c) Object between F and 2F beyond 2F                       Real                                                                 inverted, same sizes

d) Object within the focal length between F and 2F  Real                                                             inverted, diminished

 

Analysis:

  1. Do you think astronauts in the space also see the stars the way we see from the earth? Give reasons
  2. How are rainbows created in atmosphere after rains?
  3. Boojho went to a hairdresser for a hair cut. At the end of the haircut the hairdresser showed him the back of his head by holding a mirror behind his head. Explain the phenomenon behind this trick.
  4. State the whether true or false. Give reasons for your answers:  a) a beam of light emitted by the point source placed in water always diverges air   b) the refracted ray moves away from normal when a ray goes from a denser medium to a rarer medium.
  5. Why does a glass slab does not show dispersion when light falls into it, where as a prism splits light into different colors?
  6. How are butterflies eyes different from human eye?
  7. Always read from a normal distance of 30cm. Can you give reasons?
  8. For a given incident ray, the plane of the mirror makes an angle θ with the incident ray, then reflected ray is turned through 2θ. Which of the following is based on the above principle: a) periscope   b) kaleidoscope  c)  shaving mirrors  d) automobiles head lights
  9. Which of the following letter will be seen without any change in a plane mirror: i) S    ii) A  iii) T   iv) R  choose the correct option: a) i and ii   b) ii and iii   c) ii only   d) none of these
  10. Statement 1: Angle of incidence is always equal to the angle of reflection. Statement 2: law of reflection thus proves that light rays always travel in a straight line when it falls on a plain mirror. Choose the correct option: a) both 1 and 2 are correct   b) both 1 and 2 are incorrect   c) only 1 is correct  d) only 2 is correct
  11. Which of the following statement is true: a) the angle of incidence is twice the angle of reflection  b) the incident ray, the reflected ray and the normal drawn at the point of incidence lie in the same plane  c) some virtual images can be caught on the screen  d) a convex mirror forms a real image

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