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Class 7 Science — Light, shadows and reflection

Tell luminous objects from non-luminous, use the straight-line rule to explain shadows, and give the four properties of an image in a plane mirror.

Name: ________________________

Before you start

A torch, an opaque object and a screen — the three parts of a shadow set-up.

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  1. 1. Torch
  2. 2. Object
  3. 3. Screen
  4. 4. Shadow

Take away any one of the three and there is nothing to see: no light, no object to block it, or no surface for the dark patch to land on. In everyday life a wall, a floor or the ground plays the part of the screen.

  1. 1.A red ball and a blue ball of the same shape are held in the same place in front of a torch. What can you say about their shadows?

    • a) The red ball casts the darker shadow, because red is the deeper colour
    • b) One shadow is reddish and the other bluish
    • c) Both shadows are the same, because changing an object's colour does not change its shadow's colour
    • d) The blue ball casts no shadow, because blue lets light through

  2. 2.Sort each material by how much light gets through it.

    Groups: Transparent · Translucent · Opaque

    • Tracing paper
    • Thick cloth
    • Glass
    • Cardboard

  3. 3.Sort each of these by whether it gives out light of its own.

    Groups: Luminous · Non-luminous

    • A mirror
    • Lightning
    • The Moon
    • The Pole Star
    • The Sun
    • A firefly

  4. 4.A candle flame shines through a pinhole in a card onto a screen behind it. What does the image look like?

    • a) Too faint to have a shape
    • b) Upside down
    • c) The right way up
    • d) Left and right swapped, but the right way up

  5. 5.What three things do you need in order to see a shadow?

    • a) A source of light, a transparent object, and a mirror
    • b) A source of light, an opaque object, and a screen
    • c) A mirror, an opaque object, and a screen
    • d) Sunlight, a coloured object, and a dark room

  6. 6.Which set of properties describes the image formed by a plane mirror?

    • a) Smaller than the object, erect, and obtainable on a screen
    • b) Larger than the object, upside down, and laterally inverted
    • c) Same size as the object, upside down, and obtainable on a screen
    • d) Same size as the object, erect, laterally inverted, and not obtainable on a screen

  7. 7.Why is the word AMBULANCE painted reversed across the front of an ambulance?

    • a) So that it stays readable when the ambulance is moving fast
    • b) So that it can be read from a great distance
    • c) So that it looks different from ordinary vehicle lettering
    • d) So that it reads the right way round in the rear-view mirror of the vehicle ahead

  8. 8.Why do we see the Moon at night, given that it is a non-luminous object?

    • a) It glows from the heat stored in its rocks
    • b) It is lit by the lights of the Earth below it
    • c) It gives out a faint light of its own, weaker than a star's
    • d) It reflects the light the Sun casts on it

Answer key — Class 7 Science — Light, shadows and reflection

  1. 1. c) Both shadows are the same, because changing an object's colour does not change its shadow's colour
  2. 2. Glass → Transparent; Tracing paper → Translucent; Cardboard → Opaque; Thick cloth → Opaque
  3. 3. The Sun → Luminous; The Pole Star → Luminous; Lightning → Luminous; A firefly → Luminous; The Moon → Non-luminous; A mirror → Non-luminous
  4. 4. b) Upside down
  5. 5. b) A source of light, an opaque object, and a screen
  6. 6. d) Same size as the object, erect, laterally inverted, and not obtainable on a screen
  7. 7. d) So that it reads the right way round in the rear-view mirror of the vehicle ahead
  8. 8. d) It reflects the light the Sun casts on it