Light Energy – JSS1 Intermediate Science Lesson Note (Third Term)

WHAT IS LIGHT?

Imagine walking into a room at night with no windows and the power out. Can you see your chair? Can you see your shoes? No! You can only see them when you turn on a torch or a bulb.

Light is a form of energy that allows us to see the world around us. Without light, there would be no colors and everything would be dark.

Sources of Light

We get light from two main types of sources:

1. Natural Sources: These are made by nature.
   1. The Sun: Our biggest and most important source of light.
   2. Stars: Distant suns in space.
   3. Fireflies: Tiny insects that can glow.
2. Artificial (Man-made) Sources: These are made by humans.
   1. Electric Bulbs: Like the ones in our classrooms.
   2. Candles and Torches: Things we use when the power goes out.
   3. Television/Phone Screens: These give off light while we use them.

Note: The Moon is not a source of light! It acts like a giant mirror that reflects light from the sun down to Earth at night.

HOW LIGHT TRAVELS

Light is very fast—it is the fastest thing in the universe! It has one very important rule: Light always travels in a straight line.

You can test this yourself. If you try to look at a candle through a bent pipe, you won’t see anything. But if the pipe is straight, the light reaches your eye.

Luminous vs. Non-Luminous Objects

• Luminous Objects: These are things that give off their own light (like the Sun or a burning candle).
• Non-Luminous Objects: These do not make their own light. We only see them because light bounces off them and enters our eyes (like a book, a stone, or a person).

REFLECTION OF LIGHT

Have you ever wondered why you can see your face in a mirror? This happens because of Reflection.

What is Reflection?

Reflection is when light hits a surface and bounces back, just like a ball bouncing off a wall.

• Smooth Surfaces (Mirrors): These reflect light perfectly in one direction, so you see a clear image of yourself.
• Rough Surfaces (Walls/Cloth): These bounce light in many different directions, so you don’t see an image, but the object becomes visible.

The Law of Reflection

When light hits a mirror, it bounces off at the exact same angle it arrived.

• The light going in is the Incident Ray.
• The light bouncing off is the Reflected Ray.

REFRACTION OF LIGHT

Have you ever put a pencil in a glass of water and noticed that it looks “broken” or bent at the surface? This is not magic; it is Refraction.

What is Refraction?

Refraction is the bending of light as it passes from one material to another (for example, from air into water).

Why does it happen?

Light travels very fast in air, but it slows down a little bit when it enters water or glass because they are “thicker” (denser). This change in speed causes the light to bend.

Examples of Refraction:

1. A swimming pool looking shallower than it actually is.
2. A straw looking bent in a glass of juice.
3. Lenses in eyeglasses helping people see better by bending light into their eyes.

Class Activity

1. Look into a mirror. Touch your left ear with your left hand. Which hand does your “image” in the mirror use?
2. Place a coin at the bottom of a bowl of water. Try to “stab” it quickly with a pencil. Did you hit it? (Refraction makes the coin look like it’s in a different spot!)

Revision Questions

1. List three natural sources of light.
2. Why is the moon considered a non-luminous object?
3. Explain the difference between reflection and refraction.
4. What happens to light when it moves from air into a thick glass block?

Homework

Go home and find a shiny metal spoon. Look at your face in the front (the hollow part) and the back. Write down what you see. Does your face look normal, upside down, or stretched?