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.

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.
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