Light

In this article, you will be introduced to the concept of light based on the Singapore Primary 4 Science syllabus. You will also learn about the different sources of light as well as various properties of light.
 

What is Light?

Light is a form of energy that allows us to see things. Light is not a matter as it does not have mass and does not occupy space.

Light is important for plants because it is needed by them to carry out photosynthesis and make their own food. In the diagram above, we can see that a plant responds to light by growing towards it.

Sources of Light

Sources of light refers to objects that are able to give off light on their own. We are able to see them as light from the light sources enters our eyes directly. We can classify them into natural sources of light and artificial sources of light.

Natural Sources Of Light

        
The Sun - A natural source of light
Image Credits: jplenio
https://pixabay.com/photos/trees-moss-forest-sunlight-sunrays-3294681/
 

A natural light source refers to a light source that is able to give off light naturally. For example, the Sun, which lights up the Earth during the day, is a natural source of light. The stars that we see in our night sky, together with fireflies and lightning, are other examples of natural light sources.

Artificial Sources Of Light

Candle flame - an artificial source of light
Credits: Myriams-Fotos
https://pixabay.com/photos/hands-open-candle-candlelight-1926414/
 

An artificial light source refers to a light source that is man-made. The computer / tablet screen that you are reading this article on is a perfect example of an artificial light source! Other examples of artificial light sources include a candle flame, street lamps and a torchlight.

Watch our video lesson!

Properties of Light

Light travels in straight lines.                 

Light can only travel in straight lines (known as light ray) and does not bend around objects. Hence, if there is no straight path from an object to our eyes (blocked by opaque objects), we will not be able to see that object directly.

Light can be reflected.

 

Reflection refers to light bouncing off an object and changing its direction as a result. We can see objects that are not sources of light when light from a light source is reflected off the object into our eyes. 

For example, in the diagram above, light from the fluorescent light shines on the cake and is reflected by the cake into the boy’s eyes, allowing him to see the cake.

Another example will be seeing ourselves in the mirror. Light from a light source shines on us and is reflected by our body into the mirror, which then reflects the light into our eyes, allowing us to see our own reflections!

Conclusion

In this article, we learnt about what light is. We have also learnt how to classify sources of light into natural and artificial sources, and what the properties of light are. In addition, we have learnt how we are able to see objects that are not sources of light.

Test Your Concepts

Answer the following questions based on the concepts that we have covered in this article. If you get stuck, revisit the relevant section to revise the concepts.

Question 1:

Which of the following is a natural light source?

1. Moon
2. Stars
3. Mirror
4. Campfire

Solution:

(2)

Explanation: 

Stars are natural light sources. 

The Moon and mirror reflects light off them and are not sources of light. 

A campfire is considered an artificial source of light and not a natural source of light.

Question 2:

Melody set up the experiment below. She placed five identical cards with holes in a straight line in front of a lighted candle and was able to see the candle flame through the holes.

What would happen if she moved Cardboard C such that the hole is no longer in line with the rest of the cardboards?

1. The candle flame will be extinguished.
2. Melody will not be able to see the candle flame.
3. Melody will still be able to see the candle flame.
4. Light will reflect off Cardboard B and reach Melody's eyes faster.

Solution:

(2)

Explanation: 

Light can only travel in straight lines. Moving Cardboard C would cause the light from the candle flame to be blocked from entering Melody’s eyes, thus she would not be able to see the candle flame.

Question 3:

Andy is looking at the flowerpot in the room. The only light source in the room is the ceiling light.

Explain how Andy was able to see the flowerpot.

Solution: 

Light from the ceiling light shines on the flowerpot, and is reflected by the flowerpot into Andy's eyes.

Explanation: 

For Andy to be able to see the flowerpot, which is not a light source itself, light from the only light source in the room must have shone on the flowerpot before being reflected by it into Andy’s eyes.