Hands-on: Pictures from a Pinhole camera

Those from the pinhole camera compared to the real image:

The pictures from the pinhole camera are actually way clearer than these. It’s difficult to take clear pictures of them with a phone cause it’s so dark.

Image 1 - from pinhole camera

Image 1 – from pinhole camera

Image 1 - the actual scenery

Image 1 – the actual scenery

Image 2 - from pinhole camera

Image 2 – from pinhole camera

Image 2 - the real scenery (the person in the foreground was not supposed to be there)

Image 2 – the real scenery (the person in the foreground was not supposed to be there)

Lockers

Lockers

A video of the surroundings – seen from a pinhole camera:

http://youtu.be/jG30tSMqrqo

– Why can’t wordpress upload videos anyway 😡

– I apologise in advance for the shakiness.

 

 

Hands-on: Pinhole cameras

How a pinhole camera works:

How a real pinhole camera looks like:

Contrary to my belief, the images this camera showed were actually very clear! Some examples are in the next post: Hands-on: Pictures from a Pinhole camera

Side view of camera

Side view of camera

How the inside looks like.

How the inside looks like. The part where the image is shown is the screen. The rim that you see can be pulled out to increase the distance between the screen and the lens to sharpen the image.

Close-up of the lens

Close-up of the lens

Another type of pinhole camera with different pinhole sizes:

The images from this pinhole camera are not as clear as the first one. They mostly appear as tiny dots on the screen, and I could only make out the image on the screen when using the biggest hole.

The front of the camera. The different pinhole sizes can be used by rotating the circular disk.

The front of the camera. The different pinhole sizes can be used by rotating the circular disk.

Side view of camera. The back part can be slid out, just like the first camera.

Side view of camera. The back part can be slid out, just like the first camera.

Back view of camera. The rectangle inside is the screen.

Back view of camera. The rectangle inside is the screen.

Reflection – The nature of light

The article:

A brief history of light

We’re starting on a new topic:

Light

So here’s a brief history of the theories throughout history on “What is Light?”

Summarized, the theories are as follows:

  1. Tactile theory (Ancient Greece) – the eyes send out invisible probes to ‘touch’ and ‘feel’ objects around it. When these probes return, the eye can see the objects. But then, how do we see in the dark?
  2. Emission theory (Later in Ancient Greece) – the eyes emit light, which travels in rays or straight lines.
  3. Emission theory 2 (around AD 990+) –  objects emit light, which travels back to the eye.
  4. Particle/ Corpuscular theory (Newton) – light is composed of tiny particles of matter that travel through an invisible medium called “aether” that fills all empty space between objects
  5. Wave theory (Huygens) – light comprises longitudinal waves that slow down when they enter optically denser media
  6. Electromagnetism (Maxwell) – Since electromagnetic waves travel at the same speed as the measured speed of light, light is an electromagnetic wave.
  7. <Quantum theory (Einstein)> This is not covered in the article, but was mentioned in class

An observation: The explanations for what light is have graduated from ‘physical explanations’ (e.g. the tactile theory – based on what people saw in daily life) to more ‘abstract explanations’ (e.g. electromagnetism – we can’t actually see these waves, can we?)

What I’ve learnt

– The history of science can teach us many things

This article shows how theories on what light actually is have changed throughout history. In this process, scientists have continuously improved on previous scientists’ works by questioning their thinking and conducting their own experiments. In doing so, they have thus inched closer towards the truth.

  • Therefore, I’ve learnt that learning is a continuous process. Who knows, maybe the current theory on what light is may be disputed in the near future!

These scientists have also made numerous errors throughout history.

  • As such, we must be open-minded to others’ ideas. Quote from the article: “Clash of ideas is very important for science to progress since it affords an opportunity for refinements to be made as erroneous beliefs give way.”
  • A case in point is the suffocating influence of ‘giants’ in the scientific world. People were afraid to challenge Newton’s particle theory because his influence was too great – “few dared to think differently from him!”
  • As a result, people believed that “aether” existed for 2 centuries!

Lastly, great ideas that go against convention are often challenged. Thus, perseverance is important!

  • Thomas Young was belittled by other scientists, but he was eventually proved right.

How to leave comments

To the uninitiated to WordPress, here’s a quick guide:

1) At the bottom of each post, there is a link called “Leave a comment”

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The one in the middle

2) Click on it, and this box will pop up:

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3) As it says, type in your comment in the box.

4) As you type, another box will pop up below. Type in your name and email address.

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5) Finally, click on “Post comment”.

6) Easy, isn’t it? 🙂

Class exercise 4a

1. Does the shape of an object affect whether it floats or sinks? If a piece of plasticine is folded into a different shape, what changes aside from its shape?

A: Specifically, the shape of an object does not affect whether it floats or sinks, but the volume of the object that changes as its shape changes does so. For example, a lump of plasticine does not float. But if it is moulded into a cup, its volume increases, thus decreasing its density and allowing it to float.

However, if you submerge the plasticine cup, it will sink, therefore it is not the shape that allows it to float, but the increase in volume.

2. A piece of metal sinks in water, but a can (made of metal) floats in water. Why do you think this is so? Do you think the material determines whether the object sinks or floats?

A: The overall density of the can is less than that of water, as its volume is significantly greater than its mass due to the large volume of air inside it. However, the density of the piece of metal is much higher than the can’s as its volume is smaller than the can’s even though their masses are similar. Therefore, the material does not determine whether the object sinks or floats.

3. Why do some drink cans float, and some drink cans sink? Fill in the table below that will help you determine the factors that affect the density of an object.

 

Mass
(use the weighing balance)

Volume
(read off the can)

7-up

 

 

Pepsi

 

 

Coke

 

 

Coke Zero

 

 

 

Conclusion:

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Class exercise 4b – Making a density ladder

Aim: To make a density ladder, which can be used to estimate the density of some objects

Apparatus:

  • Boiling tubes
  • One cup each of: glycerine, honey, oil, coloured water
  • Droppers for each cup
  • Rubber gloves
  • Lego block
IMG_2051

From left to right: Oil, honey, glycerine and blue food colouring (to colour the water)

Procedure:

1. A density ladder can be formed by carefully adding the four liquids into a test-tube. Predict the sequence that the four liquid layers will form, starting from the bottom layer.

A: Honey, glycerine, coloured water, oil.

2. Add the liquid into the test-tube, according to the sequence you have predicted. Do not shake the test tube. Can you see four distinct layers? If not, test on another sequence, until you can see four distinctive layers of liquid forming in the test-tube. Write down the sequence (starting from the bottom layer).

A: Honey, glycerine, coloured water, oil. Our prediction is correct!

IMG_2055

Another version of the density ladder that we could take home

Another version of the density ladder that we could take home

We shook the test tube anyway... It came out like this. (It was a separate one.)

We shook the test tube anyway… It came out like this. (This is a separate one.)

3. Given that the densities of the four liquids are: 0.9 g/cm3; 1.0 g/cm3; 1.3 g/cm3; 1.4 g/cm3, match the density with the liquid. Explain your choices.

Liquid Density
Oil 0.9 g/cm3
Coloured water 1.0 g/cm3
Glycerine 1.3 g/cm3
Honey 1.4 g/cm3

A: Less dense liquids will float on top of denser liquids, therefore the densest liquid would be at the bottom, while the least dense liquid would be at the top.

4. Try dropping in the lego block. What do you observe?

A: It floats between the layer of coloured water and the layer of oil.

5. Try dropping the lego block into each liquid. What do you observe?

A: It floats in honey, glycerine and coloured water, but not in oil.

6. Estimate the density of the lego block. Give reasons for your estimation.

A: Its density is 0.95 g/cm3. As it floats in coloured water but not in oil, its density should be between 0.9 g/cm3 and 1.0 g/cm3.

Lego block suspended in honey

Lego block suspended in honey

Lego block sinking in oil

Lego block sinking in oil

Lego block floating in test tube of glycerine

Lego block floating in test tube of glycerine

Class exercise 4a – Exploring Density

On why watermelons, bowling balls and coke cans float.

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Plasticine

Is the shape of the plasticine important?

Yes Plasticine shaped into boats/cups float. Lumps of plasticine sink. The pieces of plasticine shaped into cups/boats take up more space = have more volume compared to the lumps of plasticine, even though both have the same mass. Therefore, the density of the cups/boats is smaller compared to the lumps, and they are able to float.

Drink cans

The cans all have the same shape, but do they have the same volume?

Yes All the drink cans are labeled with the same volume – 330 ml. However, some cans float while some sink. The volumes of the cans are the same, however the cans have different amounts of drink inside them. Therefore their masses are different, which affects the density of each can and thus determines whether they can float.

Coke cans

What is the difference between a can of Coke and a can of Coke Light?

 Coke Light contains artificial sweeteners while normal Coke contains sugar.  Both types of drink cans float.

 – Not sure –

Fruits

Does the skin of the fruit affect the density of the fruit?

Yes. When a whole orange is placed in the fish tank, it floats. However, when a peeled orange is placed in the tank, it sinks. The skin of the orange contains numerous air spaces which reduces the overall volume of the orange, thus reducing its density. However, when the orange peel is removed, the ratio of its mass to its volume decreases, thus its density increases and the peeled orange sinks.

Bowling ball

Does a bowling ball float or sink in water?

It will sink. The bowling ball floats in the fish tank. The density of the bowling ball is actually smaller than that of water.