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Grade 8 Science — Mirrors and lenses

Tell concave from convex for both mirrors and lenses, use the laws of reflection to find an angle, and say which of them gathers a beam and which spreads it.

Name: ________________________

  1. 1.Parallel beams of light fall on each of these. Sort them by what happens to the beams afterwards.

    Groups: Converges the beam · Diverges the beam

    • Concave lens
    • Convex mirror
    • Concave mirror
    • Convex lens

  2. 2.The angle between the normal and the incident ray has a three-word name. What is it?

  3. 3.A pen cap is held close to a concave mirror and then moved slowly away. What happens to its image?

    • a) It stays exactly the same size and the right way up
    • b) It starts upright and enlarged, then becomes inverted and gets smaller
    • c) It stays inverted and gets steadily larger
    • d) It stays upright and enlarged the whole way

  4. 4.Sunlight is directed onto a sheet of paper with a concave mirror, and the paper is moved until a small bright spot forms. What happens next, and why?

    • a) The paper can start to burn, because the mirror has concentrated the sunlight onto that point
    • b) The paper cools down, because the mirror has taken the heat out of the light
    • c) Nothing happens, because reflected light carries no heat
    • d) The spot spreads out, because a concave mirror scatters light

  5. 5.A ray of light strikes a mirror at an angle of 35° to the normal. What is the angle of reflection, in degrees? Answer with a number.

  6. 6.A ray strikes a mirror, making an angle of 40° with the normal. What angle does the reflected ray make with the mirror surface, in degrees? Answer with a number.

  7. 7.The laws of reflection were worked out with a plane mirror. Which mirrors do they hold for?

    • a) Plane mirrors and nothing else
    • b) Curved mirrors, but not plane ones
    • c) Plane and concave mirrors, but not convex ones
    • d) Plane, concave and convex alike

  8. 8.Why is a convex mirror, rather than a plane one, fitted as a vehicle's side-view mirror?

    • a) It shows a much wider area of the road behind
    • b) It shows the traffic behind the right way up, which a plane mirror cannot
    • c) It shows the traffic behind at a larger size
    • d) It is cheaper to make than a plane mirror of the same size

Answer key — Grade 8 Science — Mirrors and lenses

  1. 1. Concave mirror → Converges the beam; Convex lens → Converges the beam; Convex mirror → Diverges the beam; Concave lens → Diverges the beam
  2. 2. angle of incidence
  3. 3. b) It starts upright and enlarged, then becomes inverted and gets smaller
  4. 4. a) The paper can start to burn, because the mirror has concentrated the sunlight onto that point
  5. 5. 35
  6. 6. 50
  7. 7. d) Plane, concave and convex alike
  8. 8. a) It shows a much wider area of the road behind