## Questions and Answers on Natural Units

My responses have not been proof read.

Q
Define a new unit
Choosing the basic numerical unit for any quantity is important. It has widespread effects on both the calculations involving and, perhaps most importantly, our understanding of that quantity. To see these effects consider that we all have an intuitive idea of how 'heavy' something is if it weighs 5 kilograms, how much 'strength' a force of 5 N is, and even the definition of charge for an electron has resulted in the direction of current flow in a circuit to be opposite to that of the electron flow. Clearly the choice of this quantity must be considered carefully. What, then, would you consider to be some of the factors to taken into account when defining a new quantitative unit?
A
Many units are derived from the seven SI units. A long period is required to have a new defined units accepted. Unless it's predefined, inventing a new unit can be very confusing.

Q
Where did Avogadro's number come from? How is this constant obtained? How did Avogadro discover that there are 6.02 x 10^23 atoms per mole? Did he experimentally measure it somehow, did he allude to it in his hypothesis or was the exact number discovered later on? By what means can Avogado's number be experimentally obtained (i.e. what was done to find the value of Avogadro's number)?
A
Avogadro's number is the result of our understanding that there are certain number of particles in a given quantity. It has been obtained from many experiments. For example, it takes 96485 C to produce one mole of silver in electrolysis. The charge of an electron has been determined. These two piece of information led to a evaluation of the Avogadro's number.

Q
AC and DC
In the talk about battery cells, it seems that chemical energy can only be converted into DC current. Can chemical energy generate AC current as well?
A:
Chemical energy in oxidation-reduction reactions can be engineered to produce electric energy in the form of Daniel cells or batteries. These are DC sources. There are many electronic devices inter-converting DC and AC. As you learn more about AC and DC, you will realize how.

Q
If the electron is negatively charged, and the nucleus is positive, how do they stay separate?
A:
There is an attraction between the planets and the Sun. How the planets stay apart from the sun is about the same as how electrons stay apart from the nucleus. Energy has something to do with it.

Q
How did the theories for even simpler elements come about (ie. the string and superstring theories)? What is the scientific basis for these theories?
A:
I have not studied string and superstring theories yet, but I think these theories are trying to corelate fundamental particles and unifying the various forces.

Q
Predicting elements How were the elements that are not naturally occurring produced and were any of them predicted before they were discovered?
A
The answers are found in later modules.

Q
C-12 as the standard
In the notes it says that carbon is given an atomic mass of 12 exactly. Why is carbon given an exact mass? Why isn't its actual mass used? A: At the start, chemists use 16 as the atomic weight of oxygen. After the discovery of isotopes, a new standard is required. All concerned, C-12 is the best choice.

Q
Atomic weight
How were Atomic weights originally derived? (Note: This is different than Atomic Mass.
A
Atomic Weights were originally derived from their relative amounts in reaction with oxygen. Oxygen was assigned an atomic weight of 16

Q
Color TV
Cathode ray tube was used to deflect electron beam and form image on the TV screen but how does it display the colour of this image?
A
When striking by electrons, the fluoresce materials give lights of various wavelength, and thus various color. E = h v.

Q
Mass loss in chemical reaction
During purely chemical reactions, does the energy of the reaction, say of hydrygen and oxygen mixing into water, come from lost mass of the system?
A
Mass is lost, but undetectable in comparison to nuclear reactions.

Q
Spin of electron
Why does an electron have a spin, how do we know this is true? Alternatively, a quantum state is one where an electron can be in 2 states at the same time. How is this measurable, and how did they prove the existence of these quantum states?
A
We cannot answer why nature is nature. Spin of electron is a natural phenomenon. There are many experiments showing that there two states for an electron. Some of these are given in future lecture material.

Q
Rechargeable batter
Why can't Nickel-cadmium batteries be completely recharged? That is, how is it that they typically suffer the problem of working for a decreased amount of time after every recharge?
A
Due to a change in the property of the solids after some cycle of recharging, the recharging just cannot be revived. Many researchers are working on the problem. In fact, all rechargeable batteries have limited life, NiCd ones are worse than Li ion ones.

Q
Entropy
According to the 2nd Law of Thermodynamics, heat conversion always involves a loss, so entropy always increases. Are there any phenomena that decrease entropy?
A
In all natural spontaneous changes (reactions), entropy always increases. Changes man made do have negative entropy change.