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Learning how light bounces off surfaces and why we can see ourselves in a mirror.
Have you ever wondered why you can see your face clearly in a shiny spoon, but not in a piece of bread, even though light is hitting both of them?
Imagine throwing a rubber ball against a hard floor. What happens? It hits the floor and pops right back up! Light behaves in a very similar way. When light traveling through the air hits an object, it doesn't always stop or pass through. Instead, it often hits the surface and 'bounces' off. This process is called reflection.
We can only see the world around us because light reflects off objects and enters our eyes. If an object didn't reflect any light at all, it would look like a perfectly black hole! Most things, like your desk, your clothes, and even your pet, reflect light in many directions so we can see them from anywhere in the room.
Step-by-step observation of a simple bounce: 1. Shine a flashlight at a dark wall in a dim room. 2. Notice how the light creates a bright spot on the wall. 3. The light traveled from the bulb, hit the wall, and reflected into your eyes so you could see the spot.
Quick Check
In your own words, what is reflection?
Answer
Reflection is when light hits a surface and bounces off of it.
Why does a mirror show your face, but a white wall does not? It all comes down to how smooth the surface is. A mirror is incredibly smooth. When parallel light rays hit it, they all bounce off in the same direction. This is called specular reflection, and it creates a clear image.
On the other hand, surfaces like paper or wood might feel smooth to your hand, but under a microscope, they look like bumpy mountain ranges! When light hits these 'bumpy' surfaces, the rays bounce off in a million different directions. This is called diffuse reflection. Because the light is scattered, no clear image is formed, even though the object is still reflecting light.
Think about a lake: 1. On a very calm day, the water is perfectly flat. It acts like a mirror, showing the trees and sky. 2. If you throw a rock into the water, you create ripples (bumps). 3. The reflection disappears because the light is now hitting uneven surfaces and scattering in different directions.
Quick Check
Why can't you see your reflection in a piece of white paper?
Answer
Because the paper's surface is actually rough, which scatters the light in many different directions (diffuse reflection).
Light follows a very strict rule when it bounces, almost like a professional pool player hitting a ball off the side of a table. This rule is called the Law of Reflection.
If we draw an imaginary line straight up from the mirror (called the normal), the angle at which the light hits the mirror is exactly the same as the angle at which it bounces off. We call the incoming light the incident ray and the bouncing light the reflected ray. In math terms, if the angle of incidence is and the angle of reflection is , the rule is:
Let's use the Law of Reflection to solve a puzzle: 1. Imagine a light ray hits a flat mirror at an angle of from the normal line. 2. According to the formula , the light must bounce off at the exact same angle. 3. Therefore, the reflected ray will also be at an angle of .
What happens to light during reflection?
If a light ray hits a mirror at an angle of , what will the angle of the reflected ray be?
A piece of wood does not reflect any light at all.
Review Tomorrow
In 24 hours, try to explain to a friend why you can see yourself in a window at night but not as well during the day.
Practice Activity
Go into a bathroom with a mirror and a flashlight. Try to 'aim' the light so it bounces off the mirror and hits a specific target, like the sink handle. Notice the angles!