For parents who want their child to go on to a difficult private junior high school, it is also useful to experience for themselves how much knowledge is required to pass. Here, we will focus on science and introduce the learning content and the difficulty level required for the junior high school exam based on the reference book created by the instructor of a famous cram school. This time is the "property of light" of physics. * This article is an excerpt and re-edited from "Junior High School Examination" That's why! "
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Before I start studying light, let's talk about what it means to "see things."
Everyone can see the letters in this book now.
Why do you see it?
For example, if you turn off the lights and close the curtains to make the room pitch black, you can't see anything in the book.
Characters and things can be seen in a bright room because the light coming out of a light such as a fluorescent lamp hits the thing and the light is reflected and enters the eyes.
As you can see from the rainbow, there are many colors in light. There are three original colors, and red, blue, and green are called the three primary colors of light .
When this light is collected, it gradually becomes brighter, and when all of it is collected, the light looks white.
The screens of TVs and smartphones display images of various colors by changing the degree of light emission of these three colors.
Currently, energy-saving LEDs are used in various situations in our daily lives, but until the 21st century, ordinary light bulbs played a role. There is a reason why LEDs haven't become widespread for a long time. I couldn't make a "blue color".
You can't make white without blue. Nobody buys a TV that can't reproduce perfect colors.
Light has three properties.
The first is going straight . It means to go straight as you read it.
The second is reflection . It's rebounding.
The third is refraction . This means that it bends. When you enter something different, the light bends at the boundary.
In summary, light travels straight when traveling through the same substance, but bends at its interface when entering different objects.
There are two types of light travel, called parallel rays and diffuse rays, both of which travel straight, but there are differences in the way they travel, as shown in the following figure.
[Chart 1]Light that spreads like a light bulb is called diffuse light, and sunlight is called parallel light .
To be precise, sunlight is also a diffuse ray, but it is so large that it is so far away that it is almost parallel on the earth, so it is classified as a parallel ray.
Shadows are a typical example of what can be created by going straight through the light. If the light starts to bend, it will be difficult. The part that should be a shadow is also exposed to light and the shadow cannot be formed, so the shadow demon cannot be created.
There are other difficult things. I don't know the direction.
The human eye recognizes that there is something in the direction of the light coming in .
You can see what's in front and you can't see what's behind because the light doesn't bend.
If the light bends, the light that should not have reached will come into your eyes, and you will see something that you should not be able to see, and you will not know the direction. Just imagining it makes me scared.