IB Physics Short Note Temperature and Density

A question from Thermodynamics exam

A sample of an ideal gas is compressed by a piston from 10 m3 to 5 m3 and simultaneously cooled from 273 degrees C to 0 degrees C. As a result there is:
A. an increase in pressure
B. a decrease in pressure
C. a decrease in density
D. no change in density
E. an increase in density

Reasoning
Density refers to the mass per unit volume. First condition describes the decrease in volume, therefore density increases. Second condition describes the decrease in temperature. Base on kinetic molecular theory, molecules are closer together as energy is removed from the matter. Again, the volume decreases.

Answer
E. is the correct answer, stating “an increase in density”.

IB Physics Short Note Emissivity vs Albedo

Currently we are doing environmental physics in Physic HL and mainly talking about the energy received by Earth, for example, from the Sun.

Power radiating from an object is calculated by
P=\sigma \varepsilon AT^{4}

σ is the Stefan-Boltzmann constant, which is approximately 5.68×10-8
ɛ is the emissivity of the object’s surface

Freeman also talked albedo (e), and after doing some research online, I found that there is a difference between these two terms.

ɛ (emissivity) is the emissivity of the object’s surface
e (albedo) is the percentage of light energy being reflected away

So if the body is not transparent, ɛ+e should equal to 100% or 1.0.

CCC Style Questions Book Recommendation

Programming Challenges

Canadian Computing Competition 2015 is coming up in 4 days so it’s good time to just skim through study material again to see what I need to practice. University of Waterloo provides past contest questions and Milliken Mills High School provides unofficial solutions in Python. But as students, we always need as many problems to practice as possible so we have a comprehensive experience in all types of algorithm problems for CCC.

On CEMC website it recommends the book Programming Challenges by Skiena and Revilla (published by Springer), and honestly this is probably one of few good books that provide abundant algorithm problems and also has brief introduction in C++ and java for each topic. Personally I’m fluent in C and its dialects such as Objective-C and C++, so I find this book extremely helpful. The style of questions (how it’s presented) is similar to that of CCC, where firstly introduction is presented, then input explanation, output explanation, example input and output, and finally (sometimes) example output explanation.

This book serves as an extra resources if you have exhausted all CCC past exams available, or would like to learn about various types of problems before attacking real CCC problems.

The book is available on Amazon.ca currently for around $55, either paperback or Kindle Edition.

Breadth-First Search Algorithm in C++ implementation note

breadth-first search (BFS): Finds a path between two nodes by taking one step down all paths and then immediately backtracking.
– Often implemented by maintaining a queue of vertices to visit

Well.. CCC 2015 is on Feb. 18 so now it’s probably a good time to review all kind of stuff in C++. BFS is an important algorithm for searching paths, and here is how it works.

Pseudocode (CS106B Stanford Lecture note, distributed under CC 2.5 License):

function bfs(v1, v2):
    queue := {v1}.
    mark v 1 as visited.
    
    while queue is not empty:
        dequeue a vertex v from the queue.
        if v is v2:
            a path is found!
        for each unvisited neighbor n of v
            mark n as visited, and enqueue n in queue
     //if we get here, no path exists.

An implementation in C++ follows (CCC 2008 Senior Problem No. 3, did it quickly probably poor code style): Continue Reading…

WordPress.com themes download links for self-host (wordpress.org)

WordPress.com offers a large variety of themes, free and premium (paid). I recently found a good theme on WordPress website but the only options it gave me were to use it in wordpress.com blogs or create new ones. Of course, I self-host this blog and I’d like to be able to use it here.

I searched the name of the theme in admin panel but it doesn’t show up in the results. Then with a quick search on Google, I was able to find a svn repository for downloading all themes available to wordpress.com blogs. The link is http://themes.svn.wordpress.org/. To download these, you would need a SVN client, and on mac I recommend SmartSVN.

IB Physics Textbook Recommendation 2/6/2015

Z

IB Physics HL is a seriously fast-paced course (we think it’s more than fast-paced, but Mr. Freeman thinks we are going too slowly). Even though he would always give very detailed explanation on each topic, and the notes are available on his website, he doesn’t have time to explain every single type of questions. Also, the worksheets he provides sometimes don’t have answers, so there is no point to do them. If your method is wrong, it’ll still be wrong. So I sought for physics textbook outside of school that would benefit me by providing with answers to practice problems, and even better if detailed explanation on each questions.

Through searching one of the problems in Energy Worksheet Package, I arrived at Google Books website, and found this Fundamentals of Physics(see below), and that’s where some of the questions came from. It is a complete set of physics concepts and with abundance of problems. It also has a separate Student Solution Manual where detailed explanation with each step is provided for each problem from the book.
Continue Reading…

IB Math Free Derivative Problems Generator

Screen Shot 2015-02-05 at 9.35.14 PM

Worrying about coming up math exam on solving derivatives, I started hunting down problems on internet for practice.

I’ve known that Wolfram provides a problem generator, but only available to pro plan subscribers. $3 a month for students is not that big of a deal, but right now I don’t have needs to use it frequently enough so that $3 is actually worth it, I’ll look for some other alternatives.
Continue Reading…

3D Printed Classic Mac 128K Touchscreen Bluetooth Player – Stanford University EE47 Final Project

This is my final project for Electrical Engineering Course (EE47) at Stanford University during 2014 summer.

An Apple fan, I designed this player for the interest of recreating the design of the original Macintosh 128K. There isn’t really a need that this project is aiming to solve, it’s merely for collection purpose. I won’t be able to buy one anymore, so why shouldn’t I make one myself?

New! Updated Feb 8 2015:
Now with illuminated Apple Logo!

Continue Reading…