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 ๐Ÿ˜ก

– I apologise in advance for the shakiness.

 

 

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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.

Hands-on: Vernier calipers

Parts of a vernier caliper

 

 

Evernote Camera Roll 20130116 210623

Evernote Camera Roll 20130116 210706

Scale

Evernote Camera Roll 20130116 210717

Here I’m trying to measure the width of my eraser, which is 2.41 cm.

Other measurements:

– Pen width: 0.96 cm

– Water bottle width: 7.86 cm

– iPhone 4 width: 5.99 cm

* The picture is a little slanted, so there might be some parallax error if you look at the reading from here.

Evernote Camera Roll 20130116 210737

Using measuring instruments

Evernote Snapshot 20130112 232741

Vernier calipers

Precision: 0.1 mm, for things between 1 and 10 cm long

Typed instructions: How to use and read

Animation:

Using_the_caliper_new_en

Zero error: (measured when the jaws are closed)

  1. None – when the 0 mark of both scales are in line with each other
  2. Positive – when the 0 mark of the vernier scale is to the right of the fixed scale’s 0 mark.

How to remove: Count it from the left of the vernier scale (0 mm->). For example, if the 0.6 mm marking on the vernier scale coincides with a marking on the main scale, the zero error is +0.6 mm. Therefore, subtract 0.6 mm from the final reading.

3. Negative – when the 0 mark of the vernier scale is to the left of the fixed scale’s 0 mark.

How to remove: Count it from the right of the vernier scale (<-1.0 mm). For example, if the 0.6 mm marking on the vernier scale coincides with a marking on the main scale, the zero error is -0.4 mm instead because it is counted from the right. Therefore, add 0.4 mm to the final reading.

Micrometer screw gauge (aka MSG ๐Ÿ™‚

Precision: 0.01 mm, for things less than 1 cm long

Parts:

vfig10a

Steps:

  1. Turn the thimble until the spindle and anvil are nearly touching the object. Do not squash it!
  2. To fine-tune the measurement, turn the ratchet until it starts to click. This is when the spindle and anvil are touching the object
  3. Lock the micrometer screw gauge.

Animation:

Micrometer_no_zero_error

Zero error:

  1. None – The 0 mark on both the datum line and the thimble are in a straight line.
  2. Positive – The 0 mark on the thimble is below the datum line.

How to remove: Take the reading on the thimble and subtract it from the final reading.

3. Negative – The 0 mark on the thimble is above the datum line.

How to remove: Count the number of divisions between the 0 marks of the datum line and thimble. Add this reading to the final reading.

* Pendulum

An oscillation is one complete to-and-fro movement of the bob.

A period is the time taken to complete an oscillation.

– Only the length of the pendulum affects the period of an oscillation!

What is it used for?

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Significant Figures and calculations

Evernote Snapshot 20130112 232728

What are significant figures anyway?

(According to Google search: What are significant figures)

Each of the digits of a number that are used to express it to the required degree of accuracy, starting from the first nonzero digit.

How do you know if a digit is a significant figure?

  1. It is a non-zero number. (e.g. 122 – 3 sf)
  2. It is a zero between non-zero numbers. (e.g. 102 – 3 sf)
  3. It is a final zero after a decimal point (e.g. 2.0 cm – 2 sf)
  4. In a number < 1, it is a zero after a non-zero number (e.g. 0.20 cm – 2 sf)

Not a significant figure:

  1. Leading zeros in a number < 1 (e.g. 0.002 cm – 1 sf)
  2. In a non-decimal number, final zeros may/may not be significant

e.g. 102000 cm – may be 3/4/5/6 sf depending on the original number it is derived from

Important!

102000.00 has 8 significant figures! (Refer to rule 3)

Exam format: How to use significant figures and decimal places in calculations?

The general rule is to round the answer to the least precise measurement used in
the calculation.

Addition/ Subtraction (+/-): Follow the term with the least number of decimal places

E.g. 3.55 cm + 0.1 cm = 3.7 cm NOT 3.65 cm

Multiplication/ Division (ร—/ รท):ย Follow the term with the least number of significant figures

E.g. 4.0 m / 2 s = 2 m/s NOT 2.0 m/s

Combined measurements:

Screen Shot 2013-01-16 at 9.44.19 PM

Ignore counting numbers:

e.g. 1000 cm / 24 –> The answer will be in 4 sf (following 1000 cm)

How to use significant figures in unit conversion?

Ensure that the converted figure has the same number of significant figures as the original figure.

e.g. 0.3 m = 30 cm (as 0.3 m only has 1 sf, the converted figure 30 cm only has 1 sf too)

0.30 m = 30 cm (since 0.30 m now has 2 sf, 30 cm has 2 sf as well)

Note: Assume that all digits are sf when the original figure has final zeros.

e.g. 50 mm = 0.050 m (2 sf)

 

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