Conductor and insulator of electricity

Hi, just happen to teach on conductor of electricity. I do not know why I always have a concept the aluminium is not a conductor of electricity. But when I search the net, a few website say that is a conductor of electric. Anyway just curious and find out why some material cannot conduct electricity but some can?

The reason is thatin conductive materials, the outer electrons in each atom can easily come or go, and are called free electrons. In insulating materials, the outer electrons are not so free to move.
All metals are electrically conductive.

Electric current is the uniform motion of electrons through a conductor.

In other types of materials such as glass where atoms' electrons have very little freedom to move around. While external forces such as physical rubbing can force some of these electrons to leave their respective atoms and transfer to the atoms of another material which form the static electricity which is an unmoving, accumulated charge formed by either an excess or deficiency of electrons in an object.

For electrons to flow continuously (indefinitely) through a conductor, there must be a complete, unbroken path for them to move both into and out of that conductor.

Here will be some of the example of conductor and insulator.

Conductors: silver, copper, gold, aluminum, iron, steel, brass (copper & Zinc), bronze (copper & Tin), mercury, graphite, dirty water, concrete

Insulators: glass, rubber, oil, fiberglass, porcelain, ceramic, quartz, (dry) cotton, (dry) paper, (dry) wood, plastic, air, diamond, pure water.

Protein analysis

Hi all, please visit this website as it really give a good real life animation on how protein can be analyse. http://proteomics.cancer.gov/proteomics_basics/animation.asp

Will electricity bypass a resistance?

Hi all, I got an interesting question again from my tuition gal. She ask me about circuit as shown above. Her question is will electricity bypass a resistance like a bulb end up the bulb will not light up (like the pic on the right). I ever learn that before and think it should bypass. So to double confirm I carried out the experiment. True enough it really bypass and the bulb which is after the bypass connection did not like up.

So what if we change the direction of bypass (see pic on the left). Now we put the bulb nearer to the battery followed the bypass. Some electricity did pass through the bulb as the bulb is lighted dimly (maybe it located nearer the battery) but most of them still go through the bypass.

So you doubt maybe is my battery is weak and is not lesser electricity going through my bulb. So this picture below shows that without the bypass and using the SAME battery and SAME bulb, it actually can be lighted brightly. This can prove that most of the electricity go through the bypass.

Then I tried using a bulb with greater resistance (A). Hoping that only the bulb with lower resistance (B) will light up as I assume the electricity will bypass the bulb with lower resistance. But then both bulb still light up (see pic on the left above, the one nearer to the battery has a higher resistance). You can say that lesser electricity is pass through the Bulb (A) since it is dimmer, but I tired to change the orientation and put bulb (B) nearer to the battery. Bulb (A) is still dimmer (Not shown). So I can assume is due to the electricity from the bulb is not strong enough to light up Bulb (A). If not when Bulb (B) is placed nearer to the battery, the electricity may have pass through it (since lower resistance than bulb (A)) and bypass Bulb (A) but why both bulb still light up?

So what I can conclude from this is when there is a more direct connection of a closed circuit the electricity will choose the most direct one. However when both way is blocked by a resistance, it will not prefer the one with a lower resistance, but will still pass through both way.

The Pulley System

Hi encounter pulley system while teaching my tuition gal on forces and simple machine. So went to check out how to know the effort needed to lift the weight in different pulley system.

The mechanical advantage of each system is easy to determine. Count the number of rope segments on each side of the pulleys, including the free end. If the free end is to be pulled down, subtract 1 from this number. This number is the mechanical advantage of the system! To compute the amount of force necessary to hold the weight in equilibrium, divide the weight by the mechanical advantage!

Example in P=W, there is 1 string attached to pulley and 1 free end. Total no.s of rope segment will be 2 but it is being pulled down so substract 1. Therefore the effort needed is Weight / (2-1) = Weight/ 1. So force needed is the same as the weight.


In P=1/2 W, there is 1 string attached to pulley and 1 free end but is not being pulled down. So effort needed is Weight / 2, therefore you will only require half of the effort to move the weight.


In P= 1/4 W, there is 4 string attached to pulley and 1 free end, but it is being pulled down so substract 1. Therefore the effort needed is Weight / (5-1) = Weight/ 4. Therefore you will only require a quarter of the effort to move the weight.


Anyway special thanks to SWE organisation which gives such easy to understand formula to let us learn about pulley system. Those who want to test yourself on pulley system can also go to this link http://www.swe.org/iac/lp/pulley_act.html. Hope you have learn a lesson on it.