Force and Energy — Light Energy

Subject: Science and Technology | Topic: Force and Energy | Subtopic: Light Energy
Target age: 11 years (Kenya)

What you will learn

• What light is and where it comes from.
• Important properties of light: straight-line travel, reflection, refraction and shadow formation.
• How light is useful and how to stay safe around light sources.
• Simple experiments you can do at home or in class.

1. What is light?

Light is a form of energy that helps us see things. When light reaches our eyes, we can see colours, shapes and movement. The Sun is our main natural source of light.

2. Sources of light (everyday Kenyan examples)

• Sun (daytime) — main natural source
• Bulbs inside homes (electric bulbs, LED bulbs)
• Torches (flashlights) and phone lights
• Kerosene lamps, fire (cooking fire, candle)
• Stars at night
• Solar lights and solar panels (common in many Kenyan homes and schools)

3. Properties of light

a) Light travels in straight lines

Light moves in straight paths called rays. You can see this when a torch makes a straight beam on a wall.

b) Reflection — light bounces off surfaces

When light hits a shiny surface (like a mirror), it bounces off. Angle of incidence = angle of reflection.

c) Refraction — light bends

When light passes from air into water (or glass), it changes speed and bends. This is why a pencil looks bent in a glass of water.

d) Shadows

A shadow forms when an object blocks light. Shadows change size when the light source moves closer or further.

4. Why light is important

• Helps people and animals see and move safely.
• Plants use sunlight to make food (photosynthesis).
• Solar energy: solar panels turn sunlight into electricity for Kenyan homes and schools.
• Used in communication and medicine (e.g., small torch in clinics).

5. Simple experiments and activities

Experiment 1 — Make a shadow

Materials: torch or phone light, small toy, white wall or paper.

Steps: Place the toy between the torch and the wall. Move the torch nearer and farther. Watch how the shadow changes size and sharpness.

What to observe: When the torch is close the shadow is big and fuzzy; when it is far the shadow is smaller and sharper.

Experiment 2 — Bent pencil (refraction)

Materials: clear glass of water, pencil.

Steps: Put the pencil in the glass and look from the side. The pencil looks bent at the water surface.

Why: Light bends when it moves from air into water, making the pencil look broken or bent.

Experiment 3 — Reflection with mirror

Materials: small mirror, torch, white paper.

Steps: Shine the torch at the mirror. Angle the mirror so the light bounces onto the paper. Try different angles and see how the reflected beam moves.

Why: Light reflects from the mirror and follows the rule: angle in = angle out.

Experiment 4 — Make a small rainbow

Materials: shallow tray, mirror, water, sunny day or strong torch.

Steps: Place the mirror in the tray, fill with water so the top of the mirror is slightly covered. Aim sunlight (or torch) at the mirror so light reflects onto a white wall. You should see colours like a tiny rainbow.

Why: Water and glass split white light into colours (dispersion).

6. Safety rules

• Never look directly at the Sun — it can damage your eyes.
• Do not shine torches into people's eyes.
• Be careful with fire, kerosene lamps and hot bulbs — ask an adult for help.

7. How to save light energy at home (simple tips)

• Switch off lights when not needed.
• Use energy-saving bulbs (LEDs).
• Use solar lights and solar chargers where possible.
• Open curtains in the day to use sunlight instead of electric lights.

8. Key words (with short meanings)

• Light ray — a straight path followed by light.
• Source — where light comes from (Sun, bulb).
• Reflection — light bouncing off a surface.
• Refraction — bending of light when it goes into a different material (air to water).
• Shadow — dark area where light is blocked.
• Solar energy — energy from the Sun that can be turned into electricity or heat.

9. Short questions for practice

1. Give three sources of light you see at home. (Answer: Sun, bulb, torch/phone light)
2. What happens when light moves from air into water? (Answer: it bends — refraction)
3. How can you make a shadow larger? (Answer: move the light source closer to the object)
4. Why must we not look directly at the Sun? (Answer: it can harm the eyes)

Try the experiments with a teacher or an adult. Take notes of your observations — this helps you learn better!

Well done — you are learning about light energy!