How to make a sundial

Science Info

A sundial tells the time by the position of the sun. A shadow form on the flat surface marked with the hours of the day. As the position of the sun changes, the time is shown by the position of the shadow.

MY SHADOW

Formation of shadows

1. A shadow is formed when light is blocked by an opaque or a translucent object.

2. A shadow is formed because:  

    a) Light travel in straight line

    b) Light cannot pass through opaque object

3. The shadow is formed on the opposite side of the light source.

4. The shape of the shadow is the same as the shape of the object.

5. The changes of size of a shadow depends on:

     a) The distance between an object and the light source.

     b) The distance between an object and the screen.

     

To Show that Light Travels in Straight Lines

Experiment: To prove that light travels in straight lines

What do you need?

Three pieces of cardboard, candle, needle.

What do you do?

1. Make a hole through the centre of each of three pieces of the cardboard using a needle.

2. Place the three pieces of the cardboard upright and 30 cm apart from each other.

3. Place a lighted candle in front of the cardboard furthermost from where you stand.

4. Arrange the three pieces of the cardboard s0 that the candle flame can be seen through the holes.

5. The shift one the pieces of the cardboard to one side.

6. Try to observe the flame of candle again. Can you see it now?

What do you find?

1. We are able to see the candle flame through the hole when they are in a straight line.

2. When any one of them is not in the line with others, the candle flame will be blocked by the cardboard. Therefore the light is not visible to eye.

What do you conclude?

Light travels in straight lines.

Science Info

Light travels at high speed. It travels at about 300 000 km per second. Sunlight takes just aver 8 minutes to reach the earth. We see lighting in the sky before we hear thunder during a thurderstorm.