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Class 10 Science — Reflection and refraction of light

Apply the New Cartesian Sign Convention to the mirror and lens formulae, work out magnification and the power of a lens, and read a refractive index for what it says about the speed of light.

Name: ________________________

  1. 1.Under the New Cartesian Sign Convention, why does the object distance come out negative?

    • a) The object is below the principal axis
    • b) Object distances are measured from the centre of curvature
    • c) The object is placed to the left of the mirror, and distances to the left of the pole count negative
    • d) The object is closer to the mirror than the image is

  2. 2.For a concave mirror, match each position of the object to where the image forms.

    • Object at infinity
    • Object beyond C
    • Object at C
    • Object between C and F
    • Image beyond C
    • Image at the focus F
    • Image at C
    • Image between F and C

  3. 3.For that same lens the image distance is v = +30 and the object distance is u = -15. Magnification for a lens is m = v/u. What is m? Answer with a number, sign included.

  4. 4.A lens has a focal length of 0.5 metres. Power is the reciprocal of the focal length in metres. What is its power, in dioptres? Answer with a number.

  5. 5.The refractive index of water is 1.33. What does that number say?

    • a) Water is 1.33 times as dense as air
    • b) A ray bends through 1.33 degrees on entering water
    • c) Light travels 1.33 times as fast in water as it does in air
    • d) Light travels 1.33 times as fast in air as it does in water

  6. 6.Sort each arrangement by the kind of image it gives.

    Groups: Real and inverted · Virtual and erect

    • Object between the pole and the focus of a concave mirror
    • Object beyond the centre of curvature of a concave mirror
    • Object between the centre of curvature and the focus of a concave mirror
    • Object at the centre of curvature of a concave mirror
    • Object anywhere in front of a convex mirror

  7. 7.An optician puts two lenses in contact in a testing frame, one of power +2.0 D and one of +0.25 D. What is the power of the combination?

    • a) +2.0 D
    • b) +2.25 D
    • c) +0.5 D
    • d) +1.125 D

  8. 8.An object sits at u = -15 in front of a convex lens whose focal length is f = +10. Use 1/v = 1/f + 1/u to find the image distance v. Answer with a number, sign included.

Answer key — Class 10 Science — Reflection and refraction of light

  1. 1. c) The object is placed to the left of the mirror, and distances to the left of the pole count negative
  2. 2. Object at infinity → Image at the focus F; Object beyond C → Image between F and C; Object at C → Image at C; Object between C and F → Image beyond C
  3. 3. -2
  4. 4.
    • 2
    • +2
  5. 5. d) Light travels 1.33 times as fast in air as it does in water
  6. 6. Object beyond the centre of curvature of a concave mirror → Real and inverted; Object at the centre of curvature of a concave mirror → Real and inverted; Object between the centre of curvature and the focus of a concave mirror → Real and inverted; Object between the pole and the focus of a concave mirror → Virtual and erect; Object anywhere in front of a convex mirror → Virtual and erect
  7. 7. b) +2.25 D
  8. 8.
    • 30
    • +30