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Hi, let's try to identify parts of the optical instruments that are involved in image formation.
We are going to start off with a pinhole camera.
A pinhole camera is actually quite easy to construct.
It is basically an empty box with a tiny pinhole in the middle of one end of the box and the screen is at the opposite side of the box.
So you can grab a shoebox, open it up, and at one side of the shoebox, you can make small hole using a pin.
Well, obviously they call it a pinhole camera for a reason.
So use a pin and prick a hole here and at the other end of the shoebox, just cut it out.
After you have cut it out, replace it with a translucent plastic.
And this will become our screen.
So a pinhole camera is actually a simple project that you can do.
Maybe you can try doing it in the coming school holiday.
Now, no light will be able to enter the pinhole camera except through the tiny little hole here.
So when you are done, close the shoebox lid.
What we can do is we can experiment our pinhole camera.
So what we do is we place an object in front of the pinhole and what happens next is it will form an image.
And the image will be captured on the screen.
So whenever we shift the object to different distances, it will form different type of images.
So for this lesson, let's try to figure out what type of images that would be formed by different object distance.
So let's move to the side view of the pinhole camera.
This is the pinhole and this is the screen.
And let's just draw a few of these so we can compare it with different object distance.
So I will place an object here, maybe it is a spotlight and for the next one, I will move the object nearer.
And for the third one, let's move the object further.
So the first example, the ray will enter the pinhole camera.
So the ray on top of the object will go into the camera through the hole.
And it will form an image.
So this is the ray diagram for the first example.
And can you see that what goes into the screen will be upside down?
So let's try to practise what we learnt from the previous lesson.
If it is formed on the right hand side, what do you call it?
If the image can be captured on screen, what do you call it?
We call it real.
And now you can see that the image is actually upside down, so we call this inverted.
And how about the size of the image?
It looks kind of larger, so that is known as magnified.
So moving on to the second example where the object is closer to the pinhole.
So the light will enter the pinhole.
And it forms an image.
So we can see that the image gets really big.
So this is captured on screen, so it is real.
And it is still upside down, so it is inverted.
And this image is obviously magnified.
Now, moving on to the next example where the object is further away.
So the light from the object enters the pinhole.
And always use a ruler when drawing this.
I don't really have a ruler for this so it looks a bit weird.
So this is the ray diagram.
And please do not forget the mini arrows.
So the image is still being captured on screen, so it is real.
And it is still upside down, so it is inverted.
And the size is slightly smaller than the original though you can see it not that very different as the lines were not straight enough.
So when you practise, do use a ruler and you will get a better accurate reading.
So this is smaller and we call it diminished.
So from these three examples, we can see that we can shift the object position, the size of the image will be shifted as well.
So if I move the object nearer to the pinhole, the image formed is larger.
If I shift the object further away from the pinhole, the image formed is diminished.
And what if I put a convex lens in front of the pinhole?
What will happen?
So this is a pinhole and I put a convex lens in front of it and we know that convex lens is a focusing lens.
So convex lens is also known as converging lens.
So if my object is here, what I will get is an image, but the image will be much sharper compared to the rest of the examples that we did.
So I will get a sharper as well a brighter image.
The image will be brighter and sharper because of the convex lens.
And now let us enlarge the size of the hole.
When we do that, multiple images can be formed.
So the lines will look like this because the hole is larger.
So the image formed will be blurred.
And let's us try another example.
So let's say this is the front side of the shoebox.
And instead of one hole, we will make three holes.
What kind of image do you think will be formed?
Will it be one image or three images?
The answer is three images and we can see this on the screen at the back of it.
So we have three images that are upside down.
So hopefully through this lesson, you would know what a pinhole camera is and what does it do to the images if we change the object distance.
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