Primary Science – Light and Shadow Topic
Factors Affecting the Shadows
This science revision note aims to help your child:
– Understand how different materials affect the darkness of the shadow.
– Understand how different positions of the object affect the size of the shadow.
– How to combine two different concepts (different materials and different positions within the same exam-based question)?
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Danie had 3 sheets, A, B and C, made of 3 different materials. Each sheet is of the same size. One sheet lets almost all the light to pass through, one sheet lets some light pass through, and one sheet does not allow light to pass through. Danie arranged them in 3 different ways as shown in the setups below to create different shadows.
The shadows he observed are as shown:
What can you conclude about sheets A, B and C?
What does the darkness of the shadow tell you about how much light is able to pass through the sheet?
The darker the shadow, the less light was able to pass through. Hence, the dark black shadow is formed by the sheet that lets no light pass through (opaque sheet).
The lighter grey shadow is formed by the sheet that allowed some light to pass through (translucent sheet). If there is no shadow, that means that almost all the light was able to pass through (transparent sheet).
What does the size of the shadow tell you about the position of the sheet?
The larger the shadow, the closer the sheet is to the light source. If you have trouble understanding this, try drawing diagrams to visualise it – draw 2 diagrams, each with a torch and screen at the same position, then on each diagram, draw an object at different distances from the torch (make sure that the object in both diagrams is of identical height!):
Looking at the shadows Danie observed, let’s compare the dark black shadows first as they appear in all 3 setups.
As mentioned in Step 1, this shadow is formed by the sheet that let no light pass through.
In Step 2, we determined that the closer the sheet is to the torch, the bigger the shadow.
Comparing the sizes of the dark shadows, it was the largest in Setup 2, followed by Setup 1, then Setup 3.
Hence, in Setup 2, this sheet was the closest to the screen, followed by Setup 1, then in Setup 3, it was the furthest.
Similarly, Sheet B was closest to the screen in Setup 2, followed by Setup 1, then Setup 3.
Thus, we can conclude that Sheet B is the sheet that lets no light pass through.
To differentiate between Sheet A and C, let’s see which sheet created the lighter grey shadow.
As mentioned in Step 1, the lighter grey shadow is formed by the object that let some light pass through.
The lighter grey shadow in Setup 1 is the same size as the dark black shadow in Setup 2, meaning the sheets that created these shadows were in the same position.
In Step 3, we have found that Sheet B (which is the sheet closest to the torch in Setup 2) created the dark black shadow in Setup 2. Hence, we can determine that the sheet closest to the torch in Setup 1 created the lighter grey shadow. This sheet is Sheet A.
Thus, we can conclude that Sheet A allows some light to pass through.
Let’s check that Sheet C allows almost all the light to pass through.
Looking at Setup 3, where Sheet C is the first sheet, there is no shadow of the same size as the dark black shadow in Setup 2 and the lighter grey shadow in Setup 1. This means that the first sheet allowed most light to pass through, thus not forming a shadow.
We can thus conclude that Sheet C allows almost all the light to pass through.
FINALLY, choose the correct answer.
Question: What can you conclude about sheets A, B and C?
Answer: Sheet A allows some light to pass through (translucent), Sheet B allows no light to pass through (opaque) and Sheet C allows almost all the light to pass through (transparent).
Additional learning material for this topic
You can read the other exam-based question on light and shadows. Your child needs to apply the correct rules >>> https://scienceshifu.com/light-and-shadow-apply-the-correct-rules/
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