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Primary 4 Science for September - Light Energy

Updated: Feb 21, 2023

Here's what students can expect for Primary 4 Science for the month of September.

By now, most schools will be completing the topic on light energy. In today's blog, we will be going in-depth to some of the properties of light.

As students know by now that light can be blocked and this forms shadows, they have to know the conditions for shadow to form, lets look at this picture, conditions for shadows to from will be:

  • The presence of a light source ( in this case, the torch light)

  • The presence of an object to block the light (in this case, the ball)

  • The presence of a surface or screen that light can fall on (in this case a screen).

Secondly, they must memorise the different type of shadows that can be formed by different type of objects as shown in the table here.

Thirdly, students must also know that an object can cast shadows of different shapes and sizes depending on:

  • The position of the object

  • The position of the light source

We can look at the table here for the concepts:

Lastly, Students have to know that when different parts of the same object block the path of light, shadows of different shapes will be formed. The same object can cast shadows of different shapes.

Common question type of such topics requires knowledge recall of properties of light in terms of shadows.

Let’s look at this commonly tested question.

  • For part (a) In order to answer such questions students have to first identify the properties of glass and apply it into the scenario in the question. Since glass allows most light to pass through, it will not affect the shadow as shadow occurs due to light being blocked, thus the shadow will remain unchanged.

  • For part (b), as we are told to predict, we have to state what we can observe or see. By applying the concept that when a light source moves nearer to the object the object will block out a bigger area of light. In this case, the card will be blocking more light from the light bulb causing the shadow to become bigger.

  • For part (c), as long students understood the concept for part (b), this question is just the opposite of the concept, whereby, if we wanted the shadow to be smaller, it means that lesser light is being blocked and in order for lesser light to be blocked, the object must be further away from the light source. Thus, she can move the object nearer to the screen or move the object away from the touch.

As long students could remember and relate concepts on light in relation to shadows, they would be able to handle such questions easily.


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