Light Energy - Science Lessons for Grade 4 Students
Light is a form of energy that is very important to all life on earth. In fact, without light energy, there would be no life on earth at all.
Anything that gives out light of its own is called a source of light. The sun, the centre of our solar system, is the most important source of light for us on earth.
Plants make food using the light from the sun.
The Sun is also important to animals. Many animals eat plants or plant parts for food. The heat from the sun also helps to keep animals warm.
During the day, the sun lights up the sky and helps us to see. At night, the sun does not light up the sky. At that time, we use other sources of light to help us see.
When fuels such as gas, oil and wood burn, a flame is produced, which is a source of heat and light. Before the light bulb and other electrical devices were invented, burning fuels were widely used as a source of light. For example, a group of people living in the wild would have used fire to give them light. Candles and oil lamps are used even today.
Other examples of sources of light include fireworks and erupting volcanoes.
Some animals such as fireflies and krill are also sources of light. This is because their bodies give out light.
Electricity is an important source of energy for people because it can be converted into many other forms of energy.
If you look around your home, you will discover that many of the sources of light we use come from the conversion of electrical energy into light energy.
Some common examples include light bulbs and televisions.
Other sources of light that come from the conversion of electrical energy include traffic lights, stage lights and computer monitors.
Have you ever seen a thunderstorm and noticed the flashes of light across the sky?
The flashes of light are called lightning. As lightning gives out light of its own, it is also a source of light.
Have you ever wondered how light travels?
Light travels in a straight line from its source. Because of this, when light falls on an opaque object, it is blocked and a shadow is formed. (Remember that opaque material is material that does not allow light to pass through it. Transparent material, on the other hand, does allow light to pass through it.)
You can test it out yourself. Stand outside in direct sunlight. Take note of the shape of the shadow formed when light is blocked by your body.
You will notice that the shape of the shadow is similar to the shape of your body. If you move your body, the shadow will also move. The shape of the shadow also depends on the position of the light source. Because of this, during the day, as the sun moves across the sky, the shape and size of your shadow also will change.
How does light help us to see?
You have learnt that a source of light is anything that gives out light of its own. We are able to see things that are sources of light because the light travels from the sources and into our eyes.
A computer monitor, for example, is a source of light. You see what is on the monitor when light travels from the monitor and into your eyes.
We see a source of light when light travels from the source into our eyes.
When light falls on an object, some of the light is reflected off, or bounces off the object. This light travels to our eyes and allows us to see the object.
A good way to see how light is reflected off an object is to use a mirror. When you look at the mirror, light is reflected off your face onto the mirror. The mirror reflects the light back to the your eyes.
The moon, as you might have guessed, is not a source of light. However, it reflects some light that it receives from the sun.
Light and materials
Different materials allow different amounts of light to pass through them. Transparent materials, as mentioned above, allow light to pass through it. Glass is an object that is transparent.
If an object allows only some light to pass through it, it is called translucent material. Some examples are plastic, paper and fabric.
Opaque materials, as mentioned above, do not allow any light to pass through them. Because no light can pass through opaque objects, we are not able to see through them. Wood and metal are opaque materials.