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Hi, welcome to Form 4, Chapter 7
In this lesson, we're gonna talk about images that are formed by a plane mirror, convex lens as well as concave lens.
And all this has got to do with light because the title of Chapter 7 is known as light, colour and sight.
So what is light?
Light is a form of energy and of course the main source of light comes from our sun.
And light travels in a straight line.
And what is a plane mirror?
Well, a plane mirror is actually a piece of glass which is sculptured with a layer of silver at the back.
So it is actually a piece of a smooth glass and it is made up of a layer of silver at the back.
So the layer of silver can actually form images.
And even the polish shiny matter can be used as a mirror and do you know the spoon can be used as a mirror?
Sometimes if you use cutleries that are very well polished, you can actually see yourself in the cutleries reflection.
The formation of image by plane mirror is actually due to the reflection of light.
So let's say I place an object in front of the mirror. Let's say I put the letter F.
And what I can see in the mirror is actually the reflection of the object, right?
Or what we call the image.
Now, what are the characteristic of the images that will be formed by the mirror?
First, what we can see is the image that is formed is virtual.
Virtual means the image cannot be formed on the screen.
Next, the image is also upright.
That means if the object is facing this way, the image will also be facing the same way.
Another similar word that you can find in your book is erect.
Then, what else can we see?
We can see that the image is laterally inverted.
Laterally inverted means the left side of the image is formed by the right side of the object.
So let's take a closer look at this alphabet F.
So this is the right side of the object and this is the left side of the object.
And probably on the right side of the letter, I'll put a cross.
So in the mirror I can see a cross forming but in the mirror this will be the right hand side of the image.
And this is the left hand side of the image.
So can you see the cross for the object which I placed on the right hand side of the object when it is formed in the mirror, it actually forms on the left hand side of the image.
So this is called laterally inverted where the right would become the left and the left will become the right.
And what else can we see?
We can also see that the image formed is the same size of the object.
So let's say that the object that I'm placing has a height of 5cm.
So in the image, the height would be the same, which is 5cm.
And the other characteristic of the image that we can see is the image formed has the same distant away from the mirror as the object.
So let's say I place the object 1 meter away from the mirror.
The image that is formed would also be 1 meter away from the mirror.
So let us go through this again.
The images that are formed by a plane mirror.
So the images are virtual which means it cannot be captured on the screen.
Upright images means it face the same direction as the object.
Laterally inverted means that the right hand side will become the left hand side.
The image will have the same size as the object as well as the same distant of the object.
Now, let us move on to the lenses.
We have two types of lenses which are convex and concave.
Convex lens looks like this.
While concave lens will look like this.
Pardon my drawing, they are not exactly smooth.
So this is convex and this is concave lens.
So what is the difference between them?
Well, convex lens is thicker in the centre and thinner at the edges.
While concave is the opposite.
The middle part of the lens is thinner while the edges are thicker.
So when they form images, the images will look different from each other.
So let's talk about convex lens.
Our eyes is actually an example of convex lens.
And the characteristic of images formed by convex lens depends on the distance between the lens and the object.
Well, if the object is very near to the lens, the image that is formed will be larger compared to the object.
But when the object is farther from the lens, the image that is formed will be smaller.
So the size of the image that is formed differs depending on the distance of the object from the lens.
We will talk more in details in the coming lesson.
But generally, for a distant object, the image that is formed by the convex lens is real.
This means we can capture it on screen.
And it is inverted which means it is not facing the same direction anymore.
And for distant object, the image that is formed would be smaller compared to the object's size.
And the term that we use is diminished.
While for concave lens, the object position does not matter.
So whether we place the object closer of further to the lens, the image formed by concave lens will always be virtual.
This means it cannot be captured on screen and it will be upright or erect, which means it face the same direction as the object.
And the image will always be smaller compared to the object, we call it diminished.
And the image formed will always be on the same side of the object.
This means if we place the object on the left hand side, the image that is formed will also be on the left hand side of the lens.
So, in our coming lesson, we will focus more on the images that are formed by the convex and concave lens.
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