Grade 4 Science And Technology Force and Energy – Light Energy Notes
Science & Technology — Force and Energy
Subtopic: Light Energy
Light energy helps us see things. It comes from the sun and from lamps. In this note you will learn what light is, where it comes from, how it travels, and simple activities you can try at school or at home.
1. What is light?
Light is a form of energy that lets us see things. It moves very fast in straight lines. We get light from the sun, light bulbs and torches (flashlights). ☀️ 💡 🔦
2. Sources of light
- Natural light: The Sun is the main natural source. It helps plants grow and gives light during the day.
- Artificial light: Electric bulbs, LEDs, torches, candles and lamps (many homes in Kenya use solar lamps too).
3. How light travels
Light travels in straight lines called rays. When rays hit something, they can:
- Pass through (transparent materials).
- Be partly stopped but let some light through (translucent).
- Be stopped and make a shadow (opaque).
- Bounce off shiny surfaces (reflection).
4. Transparent, translucent and opaque
- Transparent: light passes through easily (e.g., clear glass, clean water).
- Translucent: some light passes, but you cannot see clearly through it (e.g., thin paper, frosted glass).
- Opaque: light cannot pass through (e.g., wood, metal, stone).
5. Reflection and mirrors
Light bounces off smooth, shiny surfaces. This is called reflection. Mirrors reflect most of the light so we can see our faces in them. 🪞
6. Shadows and how they form
A shadow forms when an object blocks light. The place with no light behind the object is the shadow. The size of the shadow changes with the light position — move the light closer and the shadow gets bigger.
Simple diagram: light making a shadow
7. Uses of light
- Helps us see in the day and at night (streetlights, classroom lights).
- Helps plants to make food (photosynthesis).
- Makes solar lamps work — useful in many Kenyan homes and villages.
- Used in cameras, microscopes and many machines.
8. Safety with light
- Never look directly at the sun. It can harm your eyes.
- Do not point strong lights or lasers at people's eyes.
- Be careful with candles and burning lights — keep them away from cloth.
9. Activities you can try (easy experiments)
Steps: Turn off room light. Shine the torch toward the wall. Hold the paper shape or your hand between the torch and wall. Move it closer and farther from the torch and watch the shadow size change.
Steps: Put the torch behind each item and see if light passes. Sort items into transparent, translucent, or opaque.
Steps: Put straw in the glass and look from the side. The straw looks bent where it enters the water. This shows light bends when it goes from air to water.
10. Quick questions to check you understand
- Give one natural and one artificial source of light. (Ans: Sun; Bulb or torch)
- What makes a shadow? (Ans: An object blocking light)
- Is clear glass transparent, translucent, or opaque? (Ans: Transparent)