Question 6
Place an object in front of a plane, such as a wall of your room. Shine a torch light on the object in a direction perpendicular to the wall.
What do you see?
- Light travels in straight lines from a light source (such as a torch).
- When an opaque object is placed in the path of light, it obstructs the light rays.
- The area on the surface (wall) where the light rays cannot reach appears dark, forming a shadow of the object.
Step 1 · Light Path and Obstruction
When light from the torch shines on the object, the light rays travel in straight lines toward the wall. Since the object is opaque, it blocks the path of light rays falling on it.
Step 2 · Formation of the Shadow
The rays blocked by the object cannot reach the wall, creating a dark outline on the wall where light is absent. This dark region is the shadow of the object, representing its two-dimensional projection or profile.
We see a dark region on the wall, which is the shadow of the object.
- Material Transparency: Assuming all objects form sharp shadows; transparent objects allow light to pass through without casting a prominent shadow.
- Shadow vs Object Dimensions: Confusing the 3D shape of the object with the shadow, which is always a 2D projection or silhouette.
More questions in A
Build it in Your Imagination
We will start this section by practising visualisation. For each prompt, feel free to talk to your partner, gesture, draw it in the air — but do not actually draw on paper!
- Picture your name, then read off the letters backwards. Make sure to do this by sight, not by sound — really see your name! Now try with your friend's name.
Cut off the four corners of an imaginary square, with each cut going between midpoints of adjacent edges. What shape is left over? How can you reassemble the four corners to make another square?
Mark the sides of an equilateral triangle into thirds. Cut off each corner of the triangle, as far as the marks. What shape do you get?
Mark the sides of a square into thirds and cut off each of its corners as far as the marks. What shape is left?
Net of a sphere? Experiment and see if you can make a paper cutout that can perfectly wrap around a ball without leaving any wrinkles, gaps or overlaps.
Place an object in front of a plane, such as a wall of your room. Shine a torch light on the object in a direction perpendicular to the wall.
What do you see?
Observe what happens to the size of the shadow as you vary the distance between your torch and your object.
Context: Observe what happens to the size of the shadow as you vary the distance between your torch and your object.
Q. Why does this happen?
Construct a model of a cube and use your hands to keep it balanced on one corner vertex. Can you try to understand why all the projected edges have equal length?