About Lights and Shadows

One fine evening when the sun had set and the street lights were switched on, Dhanya and I were going out for a walk to a shop nearby.
'Amma, Look there is another girl there' She exclaimed to me pointing to her shadow.
'Oh ! That is your shadow' I said.

Now questions started pouring in about shadows. I decided to explain to her in detail. But it is a bit tricky in the streets. Where are multiple sources for lights and hence multiple shadows. And these shadows all have varying sizes.

Its much easier when you go out for a walk around the noon time on a sunny day. There is only one major light source - the sun.  Here is how I explained to her.

When light falls on an you and the light cannot pass through you. You are blocking the light. You are stopping it from moving further. Hence no light reaches in front of you from behind you. Hence that area is dark as there is no light and it is your shadow.

So, We went home and picked up three different objects -

1. An opaque object - A wooden block.
2. A transparent object - A glass (plain class) of clear water
3. A translucent object - A translucent paper ( sort of semi - transparent)

We put off the lights, drew the curtains  and darkened the room. We then used a clear light source ( a candle ) and used the three objects to cast clear shadows on a plain wall.

A candle casting a shadow on a wall - Image by Paolo Neo

Now, She was able to understand the whole concept of light getting blocked. She also understood different types of objects and how you could see through some ( like glass ) and how some do not.

We also observed the kind of dark shadow caused by the wood against the light one caused by the paper.

We can use a pencil and a paper to draw how light travels from the sun, how We obscure that path and how the shadow gets formed on the ground below us.

Shadow caused by the sun.

Now, going back to the streets again,  Here are some more things to observe.

Multiple Shadows due to different light sources

• When there are multiple street lamps, walking between them causes multiple shadow.

• When we moved closer to the street lamp our shadows become smaller.  It is the smallest right under the street lamp. As we move away from the street lamp, the shadows tend to grow.

This can help the child learn that the distance between the light and the object  decide the length of the shadow. Of course,  Dhanya did  not get  it all. However, I am sure she will learn to observe more and possibly draw her own inferences.

This is a brilliant topic to discuss with kids during walks when the sun is out. The concepts can be explained slowly over a period of time gradually increasing the complexity. F

Advances topics related to shadows -

•  The size of the shadow caused by the sun in the morning, noon and evening. This will vary depending on the time of the day.
• Eclipses are nothing but shadows caused by heavenly objects.
• Learning to find the length of the shadow. Use a paper to position the sun at various places . Make the child draw straight lines from the sun to guess the size of the shadow. ( as shown above.)

• Learn more about shadows here - http://www.learnnc.org/lp/editions/earth-sun/6624